Download Idiopathic Intracranial Hypertension

FUNCTIONAL ANATOMY OF THE
CEREBROSPINAL FLUID PATHWAYS
The ventricular system:
The ventricles of the brain include the paired lateral ventricles, 3 rd and
4th ventricles.
Lateral ventricles (ventriculus lateralis):
The two lateral ventricles are irregular cavities situated in the lower
and medial parts of the cerebral hemispheres, one on either side of the
midline. They are separated from each other by a median vertical partition,
the septum pellucidum, but communicate with the 3rd ventricle and
indirectly with each other through the interventricular foramena of Monro.
They are lined by a thin membrane; the ependyma covered by ciliated
epithelium and contain cerebrospinal fluid. Each lateral ventricle is a Cshaped cavity which extends from its anterior horn in the frontal lobe in a
continuous curve posteriorly (central part), then inferiorly, and finally
anteriorly, to end in the temporal lobe as the inferior horn. From its convex
posterior surface a posterior horn extends backwards to a variable extent
into the occipital lobe.
The size and shape of this ventricle is very variable. In the young, the
walls lie almost in opposition, while with increasing age and loss of neural
tissue the ventricle expands and may reach a considerable size without an
increase in its internal pressure (Gray et al., 1995).
The anterior horn or cornu of the lateral ventricle curves inferiorly into
the frontal lobe from the interventricular foramen. It is triangular in coronal
section .The narrow floor is formed by the rostrum of the corpus callosum;
the roof and anterior wall by the trunk and genu of the corpus callosum; the
vertical medial wall by the septum pellucidum and column of the fornix;
the lateral wall by the bulging head of the caudate nucleus (Drake et al.,
2010).
The central part of the ventricle: Also called body of the lateral
ventricle, it is roofed by the trunk of the corpus callosum. Its medial wall,
which decreases in height as it is followed posteriorly, is formed by the
fornix and septum pellucidum anteriorly, and by the fornix posteriorly.
The floor consists from lateral to medial of the following structures:
The caudate nucleus.
The thalamostriate vein runs anteriorly in the groove between
thalamus and caudate nucleus.
The stria terminalis runs with the thalamostriate.
A narrow strip of the dorsal surface of the thalamus.
The choroid plexus.
The fornix: anteriorly it is a rounded bundle but posteriorly it
becomes progressively flattened and extends laterally into the floor
of the lateral ventricle.
The posterior horn or cornu begins at the splenium of the corpus
callosum, and extends posteriorly into the occipital lobe, tapering to a
point. The roof, lateral wall, and floor are formed by a sheet of fibers
(tapetum) from the splenium of the corpus callosum.
The medial wall is invaginated by two ridges; the upper of these (bulb
of the posterior horn) is formed by the fibers of the forceps major ( Skinner
et al., 2009).
The inferior horn is the direct continuation of the ventricular cavity
into the temporal lobe. It runs inferiorly, posterior to the thalamus, and then
passes anteriorly, curving medially to end at the uncus. The lateral wall is
formed by the tapetum of the corpus callosum. The roof, which can be seen
on the inferior surface of the 'frontal' part of the brain, consists of the white
matter which passes laterally into the temporal lobe. The floor is broad
posteriorly where the inferior and posterior horns meet, and is often raised
(collateral triangle) by the collateral sulcus. Anteriorly its floor narrows and
its medial part is formed by a convex ridge produced by the hippocampus
covered by a layer of nerve fibers (the aveus) which passes medially from
the hippocampus to form a ridge on its medial border (fimbria of the
hippocampus). The amygdaloid body is an oval mass of grey matter which
overlies the tip of the inferior horn of the ventricle in the uncus (Drake
JM, 1998).
Fig. (4): Ventricles of the brain (BradburyM.W.B,1985)
Fig. (5): Cast of the ventricles of the brain, left lateral aspect. In this brain, the right
posterior horn is considerably longer than the left. The key drawing indicates related
solid structures in parentheses .(Ros Lopez 2009).
The trigone of the lateral ventricle is that portion where the three
major components (body, inferior horn, and occipital horn) merge to form a
common cavity. It is indented by the bulb of the posterior horn superiorly,
the collateral eminence inferiorly, the calcaravis medially. Anteriorly in the
trigone, the glomus of the choroid plexus lies on the thalamus along with
the posterior portion of the fornix (Skinner et al., 2009).
The third ventricle:
This narrow slit like cavity lies in the median plane between the two
halves of the diencephalons. It extends from the lamina teriminalis
anteriorly, to the superior end of the aqueduct and root of the pineal
posteriorly.
The roof of the ventricle consists of a layer of ependyma which is
invaginated on each side by the overlying vascular pia mater to form a
minute, linear choroids plexus. The roof is attached on both sides to the
striamedullaris thalami.
The floor extends posteriorly from the optic recess on the superior
surface of the optic chiasma into the infundibular recess, and then passes,
above the mamillary bodies and the tegmentum of the midbrain, to the
aqueduct.(Viale et al ; 2001).
The anterior commissure indents the anterior wall of the ventricle at
the superior end of the lamina terminalis. Immediately posterior to this the
column of the fornix forms a low ridge in the lateral wall. Posterior to the
column of the fornix, and almost hidden by it, is a small, obliquely placed
aperture which opens into the lateral ventricle. This is one half of the
interventricular foramen, and it forms the only communication between the
lateral ventricles and the other cavities of the brain.
On each side, the narrow strip of choroid plexus in the roof of the
third ventricle becomes continuous with the choroid plexus of the
corresponding lateral ventricle through the interventricular foramen, and
this is often so narrow that it is nearly filled by the choroid plexus. Thus
any hypertrophy of the plexus at this situation easily blocks the
communication between the two ventricles, causing an increase in pressure
in the lateral ventricle. If this is unilateral, it may be sufficient to cause
compression of the opposite hemisphere and a shift of the midline
structures towards that side (Drake R.L,2010).
The cerebral aqueduct (aqueductus cerebri; aqueduct of
Sylvius)
Is a narrow canal, about 15 mm. long, situated between the corpora
quadrigemina and tegmenta, and connecting the third with the fourth
ventricle. Its shape, as seen in transverse section, varies at different levels,
being T-shaped, triangular above, and oval in the middle; the central part is
slightly dilated, and was named in the past, the ventricle of the mid-brain. It
is lined by ciliated columnar epithelium, and is surrounded by a layer of
gray substance named the central gray stratum: this is continuous below
with the gray substance in the rhomboid fossa, and above with that of the
third ventricle (Gray et al, 1995).
Fig. (6): Median sections. Shows important features of the brain stem and a cross
section of the midbrain. The interthalamic adhesion is indicated by an asterisk. B
emphasizes the meninges, subarachnoid space, and cisterns. Aq., aqueduct; Ep.,
epiphysis (pineal body); 1, fissure prima; 2, fissure secunda; 3 and 4, third and fourth
ventricles. The interrupted line indicates the orbitomeatal plane, which has been used
for orientation, thereby rendering the brain stem almost vertical (Swenson M.R., 2007).
The Fourth Ventricle: (ventriculus quartus):
This is the diamond shaped cavity of the hindbrain which extends
from the superior border of the pons to the middle of the medulla
oblongata. It lies behind these structures and in front of the cerebellum and
the medullary vela. It narrows above to the superior angle where it becomes
continuous with the cerebral aqueduct in the midbrain. The tiny central
canal of the inferior half of the medulla oblongata and spinal medulla opens
into it at the inferior angle (Skinner et al, 2009).
The ventricle is widest at the junction of the pons with the medulla
oblongata .Here it extends laterally on each side, to form a tubular lateral
recess, which curves over the posterior aspect of the inferior cerebellar
peduncle .This recess passes as far as the tip of the flocculus, where it
opens into the subarachnoid space through the lateral aperture (foramen of
Lushka) of the fourth ventricle, posterior to the ninth and tenth cranial
nerves. The deepest part of the ventricle is opposite the inferior part of the
pons. Immediately inferior to this, the inferior medullary velum passes
anteriorly and the ventricle becomes a shallow slit, the median part of the
thin roof of the fourth ventricle curves posteriorly on the anterior surface of
the uvula of the cerebellum to the margin of the median aperture (foramen
of Magendie) of the fourth ventricle (Badie, 2007).
By means of the lateral and median apertures the ventricle
communicates with the subarachnoid cavity, and the cerebrospinal fluid
can circulate from one to the other (Massimi L,2013).
Roof or dorsal wall superior to the cerebellar recess, the superior or
anterior medullary velum with the lingula of the cerebellum fused to its
posterior surface (Drake J.M, 1998 ).
Fig. (7): The ventricular system of the human brain (Badie, 2007)
Choroid plexus of the lateral ventricles:
Projecting into the lateral ventricle at its medial side is a highly
vascularized fringe of pia mater and ependyma, namely the choroid plexus
of the lateral ventricle, part of a larger structure, the telachoroidae. Its pial
basis is invaginated during development along a linear region of the medial
hemispheric wall the choroid fissure- where no nervous tissue develops
;hence the pia directly contacts the ventricular ependyma, the two tissues
being fused to form the choroid plexus, which otherwise consists chiefly of
small blood vessels ,capillaries and nerve fibers. It extends anteriorly to the
interventricular foramen, where it is continuous across the third ventricle
with the plexus of the opposite ventricle (Gray et al, 1995).
In the central part of each lateral ventricle, the plexus lies at the lateral
extremity of a sheet of pia mater- telachoroidae of the third and lateral
ventricles which covers the dorsal surface of the thalamus and the roof of
the 3rd ventricle (Viale et al;2001).
Choroid plexus of the third ventricle:
The roof of the 3rd ventricle is covered by and adherent to a reduplicated fold of the pia mater, the telachoroidae, from the surface of
which a pair of parasagittal vascular fringes, choroid plexuses, project
vertically downwards, invagination the ependymal roof into the cavity)
(badie, B ,2007).
The blood supply of choroid plexuses in the telachoroidae is from the
anterior choroidal branch of the internal carotid and choroidal branches of
the posterior cerebral artery, the former usually a single vessel, the latter
three to five in number. The two sets anastomose to some extent Capillaries
drain into a rich venous plexus, served by a single choroidal vein leaving
the telachoroidae, commencing near each basal (posterolateral) angle of the
tela. These veins drain directly into the internal cerebral vein or indirectly
by way of the thalamostriate vein near the foramen of Monro. These veins
also drain into the basal vein of Rosenthal directly or by way of the inferior
ventricular vein (Skinner et al, 2009).
Choroid plexus of the 4th ventricle:
These consist of two highly vascular inflexions of the telachoroidae,
which invaginate the lower part of the roof of the ventricle and are
everywhere covered by the epithelial lining of the cavity. Each consists of a
vertical and a horizontal portion: the former lies close to the middle line,
and the latter passes into the lateral recess and projects beyond its apex
(Skinner et al, 2009).
Fig. (8): The picture above shows the location of the choroid plexus in 3d-notice that it
is largely found superior to both the lateral ventricles. The lateral ventricles are
illustrated in pink, the third and the fourth ventricle is shown in green. The choroid
plexus is illustrated in red (Patel A.D, 2003).
The subarachnoid cisterns:
The arachnoid and pia mater develop from a single mass of loose
connective tissue immediately surrounding the central nervous system,
inside the dura mater. Cerebrospinal fluid from the cavities of the brain
percolates into this tissue, separating it into an outer layer, the arachnoid,
applied to the internal surface of the dura mater, and an inner layer, the pia
mater, applied to the surface of the central nervous system, with the
subarachnoid space between them.
Linings of the cavities:
The cerebrospinal fluid is separated from direct contact with its
adjacent tissues by membranes made up of single layers of cells, with or
without adjacent connective tissue; these membranes are: the ependyma,
pia mater and arachnoid.
Communication between the Ventricular System and Subarachnoid
Pathways:
Communication between the ventricular system and the subarachnoid
system in man is by way of three foramina. A median opening in the roof
of the fourth ventricle, the foramen of Magendie, establishes a
communication with the large cerebellum-medullary cistern. The lateral
recesses of the fourth ventricle wind around the medulla, passing over the
base of the inferior cerebellar peduncles. These recesses open into the
subarachnoid space on the basal aspect of the brain as the foramina of
Luschka. Each foramen is situated in the angle between the pons and
medulla, and opens into the cisterna pontis on the basal aspect of the brain
stem (Davson, 1967)
The drainage mechanism of CSF arachnoid granulations and villi:
Arachnoid granulations are wart-like projections into the dural sinuses
and are actually outgrowths of the arachnoid into the dural and the
endothelial lining of the sinuses. Arachnoid villi are also invasions of the
dura by arachnoid but on a microscopic scale.
Fig. (9): The meninges. Above panel is a midsagittal view showing the three
layers of the meninges in relation to the skull and brain. Below panels are
blowups to show details of arachnoid graduation in relation to the venous
sinus (Badie, B, 2007).
Cerebrospinal Fluid Valves:
The villus could be best described as a labyrinth of coated tubules,
from 4 to 12 microns in diameter, connecting with each of them and
opening into the subarachnoid space, on one hand, and the venous channels
of the dura on the other. These tubes may be visualized as one-way valves
that open only in one direction so as to prevent back flow of-blood into the
CSF.
The Blood-Brain Barrier and the Cerebrospinal Fluid:
There are two major types of fluid in the CNS; an interstitial fluid ISF
which accounts for 15-18% of the volume of the CNS and bathes
parenchyma keeping its internal milieu constant, and the cerebrospinal fluid
CSF.
Fig. (10): The course of the cerebrospinal fluid (CSF). Arrows lead from the
choroid plexuses of the lateral and third ventricles toward the aqueduct. The fluid
thereby formed is joined by that produced in the fourth ventricle and passes through the
median aperture to the cerebello-medullary cistern of the subarachnoid space. The
fluid then extends (1) upward around the brain and (2) downward around the spinal
cord. The inset (a coronal section at the sagittal suture) shows the drainage of the
C.S.F. into the venous system (superior sagittal sinus, S, and lateral lacunae, L, by
way of arachnoid granulations, G). Various adjacent vessels are also included. A,
cerebral artery; C, cerebral vein; 0, diploic vein; E, emissary vein; M, meningeal
vein; 3 and 4, third and fourth ventricles. The lowermost part of the figure shows the
caudal end of the spinal cord. lumbar puncture (L.P.) is performed in the part of the
subarachnoid space that lies below the termination of the spinal cord ( Skinner et al,
2009)
The blood-CSF barrier:
Secretion of the choroids plexuses is within 500 ml CSF per day and
this fluid circulated as mentioned earlier. The subarachnoid space is sealed
off by the arachnoid mater Whose cells are bonded by tight junctions. The
net flow through these membranes is normally outward: ventricular and
brain CSF diffuses into ISF and brain ISF diffuses into the subarachnoid
space.
The blood CSF barrier resides in specialized ependymal epithelium
overlying the choroidal capillaries (davson, 1967).
Fig. (11): The blood-brain and blood-CSF barriers showing the daily formation of 500
ml of CSF(swanson, M.R, 2007).
17
Anatomy of the Anterior Abdominal Wall
The abdomen represents the portion of the trunk between the thorax and
pelvis. The abdominal structure will be described from the most superficial
layer to the peritoneum.
SUPERFICIAL FASCIA.
The abdominal wall consists of skin, superficial fascia, fat, muscles,
transversalis fascia, and the parietal peritoneum. The panniculus adiposus
consists of the fat deposits in the superficial fascial layer often referred to as
Camper’s Fascia. Scarpa’s fascia is the membranous deeper layer to this,
which contains more fibrous tissue. The fibrous layer is formed by compacted
fibrous strata that are in continuity with the fatty layer.
ANTERIOR MUSCULATURE .
Much of the strength of the abdominal wall is inherent in four paired muscles
and their respective aponeuroses. These aponeuroses represent sheet-like
tendons for the insertion of the lateral muscles and also form the sheath of the
rectus abdominis. From most superficial to deep, the external oblique is the
first layer of the lateral muscles (Fig12 ). The largest of the three, the external
oblique arises from the lower 8 ribs posteriorly to interdigitate with both the
serratus and latissimus muscles. The direction of the fibers is approximately
horizontal in the uppermost portion only to become oblique in the lowest
portions as they fold on them- selves to form the inguinal ligament.
After contributing to the anterior portion of the rectus abdominis sheath, the
remaining fibers insert onto the linea alba, which is the dense white line
formed by the medial termination of all the aponeuroses. (Gray et al, 1995).
18
The internal oblique arises from the anterior two-thirds of the iliac crest and
lateral half of the inguinal ligament to run essentially at right angles to those
of the external oblique. The fibers take the shape of the iliac crest in that they
fan out to insert on the 10th to 12th ribs inferiorly.
Fig.(12) musculature of anterior abdominal wall ( external oblique – internal
oblique – tansversus abdominis – rectus abdominis ) (Gray et al, 1995).
The umbilicus marks an important level in the division of the internal oblique
aponeurosis. Above this level, the aponeurosis of the internal oblique splits to
envelop the rectus abdominis and subsequently rejoins at the linea alba.
The transversus abdominis muscles arise from the 7th to 12th costal
cartilages, iliac crest, and the lateral third of the inguinal ligament. The
muscle bundles of this group run essentially horizontally, except the lower
most medial fibers, which run a more inferomedial course to their insertion on
the pubic crest and pectin pubis.
19
The umbilicus is an important landmark in the division of the transversus
abdominis muscle fibers. Above the umbilicus the transversus abdominis
aponeurosis joins the internal oblique aponeurosis to form a portion of the
posterior rectus sheath. Below the umbilicus, the transversus aponeurosis only
contributes to the anterior rectus sheath.
Fig.(13) The rectus sheath above and below arcuate line,
(Bruni o semin ,2001).
The arcuate line (of Douglas) is the site at which termination of these
contributing fibers onto the posterior aspect of the rectus abdominis muscle
occurs.
The principal vertical muscle of the anterior abdominal wall consists of a pair
of muscles separated by the linea alba. The rectus abdominis is therefore
invested within a sheath derived from the combined aponeuroses and fasciae
of the external oblique, internal oblique, and transversus abdominis wall
consists of a pair of muscles separated by the linea alba.
20
The rectus abdominis muscle originates from the 5th through 7th costal
cartilages to insert on the symphysis pubis and crest. Superiorly, the rectus is
wide, broad, and thin, becoming narrow and thick inferiorly. The rectus
muscle and sheath form the linea semilunaris laterally. Segmentation of each
rectus muscle occurs by tendinous intersections that represent attachment of
the rectus muscle with the anterior layer of the rectus sheath .(skinner et
al,2009)
Fig.(14) The rectus sheath at various levels.(skinner et
al,2009),
Peritoneal Cavity
The abdominal viscera are contained either within a serous membrane–lined
cavity called the abdominopelvic (sometimes just “abdominal” or
“peritoneal”) cavity or lie in a retroperitoneal position adjacent to this cavity,
often with only their anterior surface covered by peritoneum (e.g., the kidneys
21
and ureters).
The abdominopelvic cavity extends from the abdominal diaphragm
inferiorly to the floor of the pelvis. The walls of the abdominopelvic cavity
are lined by parietal peritoneum, which can reflect off the abdominal walls
in a double layer called a mesentery, which embraces and suspends a visceral
structure. As the mesentery wraps around the viscera, it becomes visceral
peritoneum.
Viscera
suspended
by
a
mesentery
are
considered
intraperitoneal, whereas viscera covered on only one side by peritoneum are
considered retroperitoneal.
Anatomists refer to the peritoneal cavity as a “potential space,” since it
normally contains only a small amount of serous fluid that lubricates its
surface. If excessive amounts of fluid collect in this space due to edema
(ascites) or hemorrhage, then it becomes a “real space.” Many clinicians,
however, view the cavity only as a real space because it does contain serous
fluid but qualify this distinction further when ascites or hemorrhage occurs.
The abdominopelvic cavity is further subdivided into the following
Greater sac: most of the abdominopelvic cavity
Lesser sac: also called the omental bursa; it is an irregular part of the
peritoneal cavity that forms a cul-de-sac space posterior to the stomach and
anterior to the retroperitoneal pancreas; it communicates with the greater sac
via the epiploic foramen (of Winslow)
Additionally, the peritoneal cavity contains a variety of double-layered folds
of peritoneum in addition to the mesenteries that suspend the bowel. These
include the omenta (attached to the stomach) and peritoneal ligaments; these
are not ligaments in the traditional sense, but are short, distinct mesenteries
that connect structures (for which they are named) together or to the
abdominal wall.
22
1: Anatomy of the vertebral column:
Structure of the vertebrae
Vertebrae normally vary in size and other characteristics from one
region of the vertebral column to another and to a lesser degree within
each region; however, their basic structure is the same.
A typical vertebra could be represented by the 2nd lumbar
vertebra and consists of: Vertebral body, Vertebral arch, Seven
processes. 1 (Fig 1).
Vertebral body:
The vertebral body consists of vascular, trabecular (spongy,
cancellous) bone enclosed by a thin external layer of compact bone (Fig.
2). The trabecular bone is a meshwork of mostly tall vertical trabeculae
intersecting with short, horizontal trabeculae. The interstices of these
trabeculae are occupied by red marrow that is among the most actively
hematopoietic (blood-forming) tissues of the mature individual. One or
more large foramina in the posterior surface of the body accommodate
basivertebral veins that drain the marrow (Fig. 1). The vertebral body is
the most massive, roughly cylindrical, anterior part of the bone that gives
strength to the vertebral column and supports body weight. The size of
the vertebral bodies increases as the column descends, most markedly
from T4 inferiorly, as each bears progressively greater body weight. 1
Most of the superior and inferior surfaces of the vertebral body are
covered with discs of hyaline cartilage (vertebral end plates), which are
remnants of the cartilaginous model from which the bone develops. 2
In dried laboratory and museum skeletal specimens, this cartilage is
absent, and the exposed bone appears spongy, except at the periphery
where an epiphyseal rim or ring of smooth bone, derived from an annular
epiphysis, is fused to the body (Fig.23
1B). In addition to serving as growth
zones, the annular epiphyses and their cartilaginous remnants provide
some protection to the vertebral bodies and permit some diffusion of fluid
between the IV disc and the capillaries in the vertebral body. The superior
and inferior epiphyses usually unite with the centrum, the primary
ossification center for the central mass of the vertebral body (Fig. 1B),
early in adult life at approximately age 25.
The vertebral notches are indentations observed in lateral views of
the vertebrae superior and inferior to each pedicle between the superior
and inferior articular processes posteriorly and the corresponding
projections of the body anteriorly (Fig. 1 C & D).
The superior and inferior vertebral notches of adjacent vertebrae
and the IV discs connecting them form the intervertebral foramina (Fig.
1D), in which the spinal (posterior root) ganglia are located and through
which the spinal nerves emerge from the vertebral column with their
accompanying vessels.1
24
Figure 1: A typical vertebra, represented by L2. A. Functional components include
the vertebral body (bone color), a vertebral arch (red), and seven processes: three
for muscle attachment and leverage (blue) and four that participate in synovial joints
with adjacent vertebrae (yellow). B and C. Bony formations of the vertebrae are
demonstrated. The vertebral foramen is bounded by the vertebral arch and body. A
small superior vertebral notch and a larger inferior vertebral notch flank the pedicle.
D. The superior and inferior notches of adjacent vertebrae plus the IV disc that unites
them form the IV foramen for the passage of a spinal nerve and its accompanying
vessels. Note that each articular process has an articular facet where contact occurs
with the articular facets of adjacent vertebrae (B and D). 1
25
Figure 2. Internal aspects of vertebral body and vertebral canal. Vertebral bodies
consist largely of spongy bone, with tall, vertical supporting trabeculae linked by short
horizontal trabeculae, covered by a relatively thin layer of compact bone. Hyaline
cartilage end plates cover the superior and inferior surfaces of the bodies,
surrounded by smooth bony epiphyseal rims. The posterior longitudinal ligament,
covering the posterior aspect of the vertebral bodies and linking the IV discs, forms
the anterior wall of the vertebral canal. Lateral and posterior walls of the vertebral
canal are formed by vertebral arches (pedicles and laminae) alternating with IV
foramina and ligamenta flava.1
Vertebral arch:
The vertebral arch is posterior to the vertebral body and consists of
two (right and left) pedicles and laminae (Fig. 1A). The pedicles are short
and cylindrical processes that project posteriorly from the vertebral body
to meet two broad, flat plates of bone, called laminae, which unite in the
midline. The vertebral arch and the posterior
surface of the vertebral body
26
form the walls of the vertebral foramen (Fig. 1 B & C).
The succession of vertebral foramina in the articulated vertebral
column forms the vertebral canal (spinal canal), which contains the spinal
cord and the roots of the spinal nerves that emerge from it, along with the
membranes (meninges), fat, and vessels that surround and serve them
(Fig. 3 E)1.
Figure 3. Vertebral column and vertebral canal, demonstrating its five regions.
A. This anterior view shows the isolated vertebral column. B. This right lateral view
shows the isolated vertebral column. The isolated vertebrae are typical of each of the
three mobile regions. Note the increase in size of the vertebrae as the column
descends. C. This posterior view of the vertebral column includes the vertebral ends
of ribs, representing the skeleton of the back. D. This medial view of the axial
skeleton in situ demonstrates its regional curvatures and its relationship to the
cranium (skull), thoracic cage, and hip bone. The continuous, weight-bearing column
of vertebral bodies and IV discs forms the anterior wall of the vertebral canal. The
lateral and posterior walls of the canal are formed by the series of vertebral arches.
The IV foramina (seen also in part B) are openings in the lateral wall through which
spinal nerves exit the vertebral canal. The posterior wall is formed by overlapping
laminae and spinous processes, like shingles on a roof. E. This sagittal MRI study
shows the primary contents of the vertebral
27 canal. The medullary cone (L. conus
medullaris) is the cone-shaped inferior end of the spinal cord, which typically ends at
the L1-L2 level in adults. The dura mater, the external covering of the spinal cord
(gray), is separated from the spinal cord by a fluid-filled space (black) and from the
wall of the vertebral canal by fat (white) and thin-walled veins (not visible here). 1
Seven processes arise from the vertebral arch of a typical vertebra
(Fig. 1A&C):
One median spinous process projects posteriorly (and usually
inferiorly, typically overlapping the vertebra below) from the vertebral
arch at the junction of the laminae.
Two transverse processes project posterolaterally from the
junctions of the pedicles and laminae.
Four articular processes (zygapophyses) two superior and two
inferior also arise from the junctions of the pedicles and laminae, each
bearing an articular surface (facet).
The former three processes, one spinous and two transverse, afford
attachments for deep back muscles and serve as levers, facilitating the
muscles that fix or change the position of the vertebrae.
The latter four (articular) processes are in apposition with
corresponding processes of vertebrae adjacent (superior and inferior) to
them, forming zygapophysial (facet) joints (Fig. 1 D).
Through their participation in these joints, these processes
determine the types of movements permitted and restricted between the
adjacent vertebrae of each region. They also assist in keeping adjacent
vertebrae aligned, particularly preventing one vertebra from slipping
anteriorly on the vertebra below. Generally, the articular processes bear
weight only temporarily, as when one rises from the flexed position, and
unilaterally when the cervical vertebrae are laterally flexed to their limit.
However, the inferior articular processes of the L5 vertebra bear weight
even in the erect posture.1
Vertebral canal
The spinal cord lies within a bony canal formed by adjacent
vertebrae and soft tissue elements (the
28 vertebral canal) : the anterior wall
is formed by the vertebral bodies of the vertebrae, intervertebral discs,
and associated ligaments; the lateral walls and roof are formed by the
vertebral arches and ligaments.3
Within the vertebral canal, the spinal cord is surrounded by a series
of three connective tissue membranes called the meninges.
The meninges
The pia mater is the innermost membrane and is intimately
associated with the surface of the spinal cord;
The second membrane, the arachnoid mater, is separated from the
pia by the subarachnoid space, which contains CSF;
The thickest and most external of the membranes, the dura mater,
lies directly against, but is not attached to, the arachnoid mater.3
Contents of the vertebral canal
The spinal cord, spinal nerve roots, and spinal meninges and the
neurovascular structures that supply them are located within the vertebral
canal (Fig. 4).1
In the vertebral canal, the dura mater is separated from surrounding
bone by an extradural (epidural) space containing loose connective tissue,
fat, and a venous plexus.3
29
Figure 4: Innervation of periosteum and ligaments of vertebral column and of
meninges. Except for the zygapophysial joints and external elements of the vertebral
arch, the fibroskeletal structures of the vertebral column (and the meninges) are
supplied by the (recurrent) meningeal nerves. Although usually omitted from
diagrams and illustrations of spinal nerves, these fine nerves are the first branches to
arise from all 31 pairs of spinal nerves and are the nerves that initially convey
localized pain sensation from the back produced by acute herniation of an IV disc or
from sprains, contusions, fractures, or tumors of the vertebral column itself. (Based
on Frick H, Kummer B, Putz R: Wolf-Heidegger's Atlas of Human Anatomy, 4th ed.
Basel, Karger AG, 1990:476.) 1
Spinal cord
The spinal cord is the major reflex center and conduction pathway
between the body and the brain. This cylindrical structure slightly
flattened anteriorly and posteriorly, is protected by the vertebrae and their
associated ligaments and muscles, the spinal meninges, and the CSF. The
spinal cord begins as a continuation of the medulla oblongata (commonly
30
called the medulla), the caudal part of the brainstem. In adults, the spinal
cord is 42-45 cm long and extends from the foramen magnum in the
occipital bone to the level of the L1 or L2 vertebra. However, its tapering
inferior end, the medullary cone, may terminate as high as T12 vertebra
or as low as L3 vertebra. Thus the spinal cord occupies only the superior
two thirds of the vertebral canal.1
The spinal cord is enlarged in two regions in relationship to
innervation of the limbs. The cervical enlargement extends from the C4
through T1 segments of the spinal cord, and most of the anterior rami of
the spinal nerves arising from it form the brachial plexus of nerves that
innervates the upper limbs. The lumbosacral (lumbar) enlargement
extends from T11 through L1 segments of the spinal cord, inferior to
which the cord continues to diminish as the medullary cone. The anterior
rami of the spinal nerves arising from this enlargement make up the
lumbar and sacral plexuses of nerves that innervate the lower limbs.1
The external surface of the spinal cord is marked by a number of
fissures and sulci: The anterior median fissure extends along the length of
the anterior surface; the posterior median sulcus extends along the
posterior surface; the posterolateral sulcus on each side of the posterior
surface marks where the posterior rootlets of spinal nerves enter the
cord.3
Spinal nerve roots
Each spinal nerve is connected to the spinal cord by posterior and anterior
roots:
The posterior root contains the processes of sensory neurons
carrying information to the CNS .The cell bodies of the sensory neurons,
which are derived embryologically from neural crest cells, are clustered
in a spinal ganglion at the distal end of the posterior root, usually in the
intervertebral foramen.
The anterior root contains motor nerve fibers, which carry signals
away from the CNS. The cell bodies31of the primary motor neurons are in
anterior regions of the spinal cord .Medially, the posterior and anterior
roots divide into rootlets, which attach to the spinal cord. 3
In embryos, the spinal cord occupies the full length of the vertebral
canal, thus spinal cord segments lie approximately at the vertebral level
of the same number, the spinal nerves passing laterally to exit the
corresponding IV foramen. By the end of the embryonic period (8th
week), the tail-like caudal eminence has disappeared, and the number of
coccygeal vertebrae is reduced from six to four segments. The spinal cord
in the vertebral canal of the coccyx atrophies. During the fetal period, the
vertebral column grows faster than the spinal cord; as a result, the cord
ascends relative to the vertebral canal.1
At birth, the tip of the medullary cone is at the L4-L5 level. Thus,
in postnatal life, the spinal cord is shorter than the vertebral column;
consequently, there is a progressive obliquity of the spinal nerve roots
(Fig 5). Because the distance between the origin of a nerve's roots from
the spinal cord and the nerve's exit from the vertebral canal increases as
the inferior end of the vertebral column is approached, the length of the
nerve roots also increases progressively. 1
The lumbar and sacral nerve roots are therefore the longest,
extending far beyond the termination of the adult cord at approximately
the L2 level to reach the remaining lumbar, sacral, and coccygeal IV
foramina. This loose bundle of spinal nerve roots arising from the
lumbosacral enlargement and the medullary cone and coursing within the
lumbar cistern of CSF caudal to the termination of the spinal cord
resembles a horse's tail, hence its name ”the cauda equine” ( horse tail).1
Arising from the tip of the medullary cone, the terminal filum
descends among the spinal nerve roots
32 in the cauda equina. The terminal
filum (filum terminale) is the vestigial remnant of the caudal part of the
spinal cord that was in the tail-like caudal eminence of the embryo. Its
proximal end (the pial part or internal terminal filum) consists of vestiges
of neural tissue, connective tissue, and neuroglial tissue covered by pia
mater. The terminal filum perforates the inferior end of the dural sac,
gaining a layer of dura and continuing through the sacral hiatus as the
dural part or external terminal filum (also known as the coccygeal
ligament) to attach to the dorsum of the coccyx. The terminal filum is an
anchor for the inferior end of the spinal cord and the spinal meninges. 1
33
Figure 5. Vertebral column, spinal cord, spinal ganglia, and spinal nerves. Lateral
and posterior views illustrating the relation of the spinal cord segments (the
numbered segments) and spinal nerves to the adult vertebral column.
34
1
The Cerebrospinal Fluid (CSF) is produced by vascular plexuses in the
Ventricles. All of the ventricles are filled with a clear, watery fluid, the
cerebrospinal fluid (CSF). Most of the fluid is produced by vascular tufts
the choroid plexus. This is present in all four ventricles, but the largest
amount is found in the lateral ventricles. The choroid plexuses are
attached to the wall of the ventricles with thin stalks (tela choroidea). The
average volumes of CSF are (Damkier et al. 2013):
1. 50 mL in the newborn and increases with age.
2. 90 mL in children 4 to 13 years old.
3. 150 mL in adults.
The rate of formation is approximately 0.35 ml/min or 500
ml/day. Approximately 14% of total volume turns over every
hour. The rate at which CSF forms remains relatively constant
and declines only slightly as CSF pressure increases. In
contrast, the rate of absorption increases linearly as CSF
pressure exceeds 7 mm Hg. At a pressure of 20 mm Hg, the
rate of absorption is three times the rate of formation
(Damkier et al. 2013).
35
The capacity for drainage is two to four times the normal rate of CSF
production. The villi can behave as one-way valves, in that they are
closed by high pressure in the venous sinus and opened by high CSF
pressure (Barshes et al. 2005).
CSF production
Most of the CSF is produced within the ventricular system by the choroid
plexus. However, a sizable proportion some 10% to 20%, evidently is
formed by the parenchyma of cerebrum and spinal cord. The accepted
view is that CSF bulk flow occurs from the site of its production in the
ventricles to its absorption in the arachnoid granulations. In the adult
human, production of CSF is independent of pressure however; a
prolonged and marked increase in intraventricular pressure owing to
hydrocephalus can slightly reduce the rate of CSF formation (Ross &
Lamperti 2010).
CSF appears to be formed in a two-step process:
The 1st step is the formation by hydrostatic pressure of a plasma ultrafiltrate through the non-tight-junction choroidal capillary endothelium
into the connective tissue stroma. The passage is driven by hydrostatic
pressure.
The 2nd step is ultra-filtrate transformation subsequently into a secretion
by an active metabolic process within the choroidal epithelium. The
astrocytic surface extrudes sodium into the ventricle, followed by
osmotically drawn water (Damkier et al. 2013).
19
36
Anatomy & Physiology
CSF absorption
80% enters directly into the cisternal system with subsequent drainage
from the cerebral subarachnoid space into the cortical venous system,
20% circulates into the subarachnoid space of the spinal cord. Yet Spinal
descent of CSF however, might prove to be an important alternative
pathway in pathologic conditions. CSF drainage occurs in part by way of
the arachnoidal villi and granulations. These are essentially microtubular
invaginations of the subarachnoid space into the lumen of large dural and
venous sinuses (Barshes et al. 2005). Three factors control CSF
drainage:
1-CSF pressure:
The normal CSF pressure at the reference level (the foramen of Monro) in
the recumbent adult is 100-200mm H2O (7-15mmHg) with mean
pressures of 20mmHg regarded as elevated. Pressures from 0-7mmHg do
not usually signify any pathology. The CSF pressure fluctuates with the
arterial pulse wave and respiratory excursions.
2-Pressure within the dural sinuses and the cortical venous system: CSF is
absorbed into the venous system through the arachnoid villi associated
with the major dural sinuses, predominantly the superior sagittal sinus.
The present view proposes a hydrostatic pressure-dependent system
between the CSF and venous sinus blood with an opening threshold
(Schaller 2004).
3-Resistance of the arachnoid villi to CSF flow
Changes in any of these variables significantly affect CSF flow. It
appears that drainage does not depend on the colloid osmotic pressure
37
20
Anatomy & Physiology
difference between CSF
and sinus blood because the tubules are
permeable to protein (Schaller 2004).
CSF also can drain through the lymphatics as it was observed that
children with an obstructed CSF-diverting shunt occasionally develop
nasal congestion and periorbital or facial swelling. The lymphatic
drainage of CSF might play a role in the pathophysiology of
hydrocephalus, either as an alternative pathway for drainage or in cases of
impaired access to the lymphatic system, as a cause of hydrocephalus.
Also the periventricular hypodensity in the presence of hydrocephalus
which is seen at CT and MRI scans is the result of CSF migrating into the
area surrounding the ventricles in the presence of increased
intraventricular pressure. CSF also can drain from the subarachnoid
spaces surrounding the cranial and spinal nerve root sleeves, with entry
into the lymphatic system (Sakka et al. 2011).
CSF circulation in brain
CSF passes from the paired lateral ventricles through foramina of Monro
into the single midline third ventricle, and then flows down the single
midline aqueduct of Sylvius into the single midline fourth ventricle. CSF
leaves the ventricular system through the two lateral foramina of Luschka
and the midline foramen of Magendie. Here CSF is shown exiting
through the foramen of Magendie and entering the cisterna magna.
Within the subarachnoid space CSF flows over the convexities of the
brain and the folia of the cerebellum and around the brainstem. From the
cisterna magna CSF also courses inferiorly to surround the spinal cord
(Sakka et al. 2011).
38
21
Anatomy & Physiology
The cerebrospinal fluid becomes blood plasma again and the rate of
reabsorption normally equals the rate of production (Hamilton et al.
2012).
Figure 9: CSF flow from choroid plexus to their absorption in the arachnoid villi. Quoted
from (Damkier et al. 2013).
CSF Functions
Since cerebrospinal fluid is tissue fluid, one of its functions is to bring
nutrients to CNS neurons and to remove waste products to the blood as
the fluid is reabsorbed. The other function of cerebrospinal fluid is to act
as a cushion for the central nervous system. The brain and spinal cord are
enclosed in fluid-filled membranes that absorb shock. Naturally this
protection has limits very sharp or heavy blows to the skull will indeed
cause damage to the brain (Schaller 2004).
39
22
Anatomy & Physiology
CSF flow dynamics
The flow is a result of cardiac pulsations transmitted to intracranial
arteries and capillaries, causing a specific series of CSF and brain
parenchyma displacements. In normal conditions, CSF shows an
alternating upward (diastolic) and downward (systolic) motion in each
cardiac cycle that can be recognized and measured in the ventricular
system, cisterns, and subarachnoid spaces. In healthy persons, antegrade
flow of CSF is initiated at the foramen of Monro at 8% of the cardiac
cycle.
The wave of CSF flow continues through the aqueduct into the proximal
fourth ventricle. At the time CSF is flowing in an antegrade direction
through the aqueduct it is also flowing in an antegrade direction through
the pontine cistern and upper cervical subarachnoid space. Onset of
retrograde flow is initiated at 42% of the cardiac cycle, first in the
posterior cervical subarachnoid space and lower fourth ventricle followed
by retrograde flow starting in the aqueduct at 54% of the cardiac cycle,
and then in the anterior cervical subarachnoid space. In healthy subjects
ventricular CSF systole and diastole are constantly slightly out of phase
with CSF systole and diastole in the subarachnoid space (Barshes et al.
2005).
Arterial expansion causes brain movement and expansion of the central
and lower parts of the brain acts as an expanding and retracting piston,
which causes the CSF pulsation at the foramen magnum. Based on
observations that CSF pulse pressure varies with cardiac and respiratory
cycles it was concluded that CSF pulsation is due to changes in brain
blood volume caused by arterial expansion (Sakka et al. 2011).
The arterial expansion starts 100 ms after the R-wave in the ECG
complex and has a fixed duration of about 300 ms. The brain expansion
40
23
Anatomy & Physiology
starts 60 ms later than the arterial one and occupies half of the cardiac
cycle, i.e. 400–500 ms. Of outmost importance to intracranial dynamics is
the direct volume conduction of the pulse wave from the expanding
extracerebral arteries to the veins and spinal canal (Sakka et al. 2011).
the total volume of the four main intracranial components i.e. the brain,
the CSF, the arterial and the venous blood, is constant and that any
volume increase in one component causes a matching decrease in the
other components so The systolic expansion of the intracranial arteries is
thus balanced by a matching expulsion of CSF through the foramen
magnum and expulsion of blood from the veins into the dural venous
sinuses.
The systolic volume increase of the brain is about 0.03 ml. The minute
brain expansion occurs inwards towards the ventricular system and equals
the systolic stroke volume in the aqueduct (0.03 ml/beat) (Bradley 2014).
24
41
Clinico-pathology of HII
under high pressure and turbulence through smooth walled venous
stenoses related to transverse sinus collapse from high CSF pressure
(Farb et al. 2003).
Ophthalmoscopic examination
Papilledema, optic disc edema due to increased intracranial pressure, is
the cardinal sign of BIH. Optic disc edema either directly or indirectly is
the cause of visual loss of BIH. The higher the grade of the papilledema,
the worse the visual loss is. But, in the individual patient, the severity of
visual loss cannot accurately be predicted from the severity of the
papilledema. A partial explanation for this is that with axonal death from
compression of the optic nerve, the amount of papilledema decreases
(Scott et al. 2010).
42
39
Clinico-pathology of HII
Frisén (table 2) has proposed a useful staging scheme for papilledema
with good sensitivity and specificity based on the ophthalmoscopic signs
of disturbed axoplasmic transport. It has been modified recently with a
key finding added for each stage or grade (Frisén 1982).
Table 2: Frisén papilledema scale. Stage 0 Normal Optic Disc (figure 11)
• Blurring of nasal, superior and inferior poles in inverse proportion
to disc diameter.
• Radial nerve fiber layer (NFL) without NFL tortuosity
• Rare obscuration of a major blood vessel, usually on the upper pole
Stage 1 - Very Early Papilledema (figure 12)
• Obscuration of the nasal border of the disc
• No elevation of the disc borders
• Disruption of the normal radial NFL arrangement with grayish
opacity accentuating nerve fiber layer bundles
• Normal temporal disc margin Subtle grayish halo with temporal
gap (best seen with indirect ophthalmoscopy)
• Concentric or radial retrochoroidal folds.
Stage 2 - Early Papilledema
• Obscuration of all borders Elevation of the nasal border
• Complete peripapillary halo.
Stage 3 - Moderate Papilledema
• Obscurations of all borders
• Increased diameter of optic nerve head
• Obscuration of one or more segments of major blood vessels
43
Clinico-pathology of HII
leaving the disc Stage 4 - Marked Papilledema
(figure 13)
• Elevation of the entire nerve head
• Obscuration of all borders Peripapillary halo
• Total obscuration on the disc of a segment of a major blood vessel Stage 5 Severe Papilledema
• Dome-shaped protrusions representing anterior expansion of the optic nerve
head
• Peripapillary halo is narrow and smoothly demarcated
• Total obscuration of a segment of a major blood vessel may or may not be
present
• Obliteration of the optic cup.
44
Clinico-pathology of HII
crania
l
nerve
s that
make
nearly
a 90°
bend
(CN
II, VI,
VII)
appea
r to be
susce
ptible
to
dama
ge at
Figure 13: Stage IV papilloedema.
the
site of
the
Ocular motility disturbances
bend
Horizontal diplopia is reported by about 1/3 of BIH
(Ache
patients and sixth nerve palsies are found in 10-20%.
son
Motility disturbances other than sixth nerve palsies have
2006)
been
.
reported.
Some
of
these
reflect
erroneous
conclusions from the small vertical ocular motor
imbalance that is known to accompany sixth nerve
palsies. Bell's type palsies of CN VII rarely occur and are
usually transient. The common thread
here is that the
45
OF ABBREVIATIONS
2D-TOF: Two-dimensional time-off light
3D-PC: Three-dimensional phase-contrast
ANA: Antinuclear antibody
ANCA: Antinuclear cytoplasmic antibodies
BMI: Body Mass Index
cd/m2: candle/ meter square
CSF: Cerebrospinal fluid
CT: Computed tomography
cVEP: conventional visual evoked potential
CVST: Cerebral venous sinus thrombosis
EDI: Electro-Diagnostic Imaging
EEG: Electroencephalography
ESR: Erythrocyte sedimentation rate
FSH: Follicular stimulating hormone
g/dl: gram/decilitre
HVF: Humphrey Visual Field
ICHD: International Classification of Headache Disorders
ICP: Intracranial pressure
IIH: Idiopathic intracranial hypertension
46
I
ION: Ischemic optic neuropathy
ISCEV: International society of clinical electrophysiology of vision
LH: Luteinizing hormone
mfERG: multifocal electroretinogram
mfVEP: multifocal visual evoked potential
MRI: Magnetic resonance imaging
MRV: Magnetic Resonance venography
NSAID: Non-steroidal anti-inflammatory drugs
OD: oculus Dexter (the right eye)
ON/MS: Optic neuritis/Multiple sclerosis
ONSD: Optic nerve sheath distension
OS: oculus Sinister (the left eye)
OSA: Obstructive sleep apnea
PCO: Polycystic ovary syndrome
TS: transverse sinus
TSH: Thyroid stimulating hormone
TVOs: Transient visual obscurations
VA: Visual acuity
47
II
Idiopathic Intracranial Hypertension
Idiopathic Intracranial Hypertension
Historical Background:
Idiopathic intracranial hypertension is the most recent of a number of
names for the clinical syndrome of elevated intracranial pressure, without
enlargement of the cerebral ventricles and in the absence of space occupying
lesions. The German physician Heinrich Quincke published what is widely
regarded as the first description of the condition, calling it „meningitis serosa
‟. This appeared to be preceded by case reports describing the same condition
as early as 1866 (Johnston et al, 2007).
By the turn of the 20th century, the terms serous meningitis and
pseudotumour cerebri had been adopted, but diagnosis relied on clinical
features or post mortem findings. Cerebral pneumography permitted further
study of the condition in live patients and this was later to be enhanced by
ventriculography and encephalography (Davidoff, 1965).
The term benign intracranial hypertension was used for many years
until several reports of severe visual loss in the condition rendered the term
„benign‟ inappropriate (Foley, 1955).
However, in view of the potential for devastating loss of vision
associated with papilledema, Corbett and Thompson removed the adjective
“benign” and substituted “idiopathic.” Idiopathic intracranial hypertension
denotes the condition of increased ICP without an obvious underlying brain
pathological condition (Corbett and Thompson, 1989).
4
48
Idiopathic Intracranial Hypertension
Definition:
Idiopathic intracranial hypertension is a syndrome of increased
intracranial pressure (ICP) without ventriculomegaly or mass lesion, and
with normal cerebrospinal fluid composition (Bandyopadhyay, 2001).
With the advent of complex neuro-radiology, it has been possible to
identify intracranial lesions and vascular pathologies in patients who might
previously have been labelled as having IIH by one of its many names
(Friedman and Jacobson, 2002).
Older reports were likely to have included patients in whom cerebral
venous sinus thrombosis (CVST) had not been excluded since imaging
techniques were in their infancy. The clinical presentation of CVST is
identical to that of IIH, but the outcome and management is dramatically
different and CVST carries a significantly worse prognosis. It is essential
that CVST is excluded before a diagnosis of IIH is made (Friedman and
Jacobson, 2002).
The diagnostic criteria have undergone several modifications over the
years. Strict criteria now exist to ensure that a diagnosis of IIH is only
applied to patients in whom all other causes of intracranial hypertension
have been excluded (Friedman and Jacobson, 2002). These are shown in
table (1) and are often referred to as „modified Dandy criteria‟ (Friedman
and Jacobson, 2002).
5
49
Idiopathic Intracranial Hypertension
Table (1): Diagnostic criteria of idiopathic intracranial hypertension „modified Dandy
criteria‟ (Friedman and Jacobson 2002)
1. If symptoms and / or signs are present, they may only reflect those of
generalised intracranial hypertension or papilledema with no localizing signs
except an abducens nerve palsy.
2. Intracranial pressure, as measured in the lateral decubitus position, is
elevated at least 25 cm H2O.
3. The composition of the cerebrospinal fluid is normal
4. There is no evidence of hydrocephalus, mass, structural or vascular lesion
5. Normal brain imaging that does not identify a cause for elevated ICP
Despite widely accepted criteria, controversy still surrounds the
definition of IIH as a discrete clinical entity. Pseudotumour cerebri
syndrome is still used by many to describe patients with the condition, as an
„umbrella‟ term that can include those cases where a causative factor is
strongly suspected (Johnston et al., 2007). Nomenclature:
The nomenclature for IIH remains controversial. “Benign intracranial
hypertension” is no longer accepted, as significant visual morbidity may
occur with this disorder (Corbett et al., 1982).
The term “pseudotumour cerebri,” a historically popular and allencompassing term, leaves the impression that IIH is not a real disease. IIH
is the favored term for the primary (idiopathic) disorder (Wall and George,
1991).
6
50
Idiopathic Intracranial Hypertension
Epidemiology:
• Incidence:
Early attempts to measure the incidence of IIH, or the syndrome by
one of its alternative names, are likely to have overestimated the number of
cases, due to the inclusion of intracranial hypertension secondary to venous
sinus thrombosis or other conditions difficult to elicit by older investigative
techniques. In addition, most of the largest studies of incidence were
completed prior to the widespread acceptance of the modern diagnostic
criteria so the actual incidence of „truly idiopathic‟ IIH is by no means
certain (Friedman and Jacobson, 2002).
Around the world, a small number of population studies have
attempted to measure the overall incidence (table 2).
Table (2): Number of population studies to measure the overall incidence of IIH (Kesler et
al., 2001 and Raoof et al., 2011)
Year
Location
Author
Population
IIH Incidence
per 100,000
0.9
1.07
1988
Iowa, USA
Durcan et al. (1988)
size
2,913,808
1988
Louisiana, USA
Durcan et al. (1988)
4,480,681
1993
Benghazi, Libya
Radhakrishnan et al. 519,000
2.2
2000
Hokkaido, Japan
(1993)
Yabe et al. (2000)
5,780,000
0.03
2001
Belfast, Ireland
Craig et al. (2001)
1,640,000
0.6
2011
Sheffield, UK
Raoof et al.(2011)
3,520,000
1.56
7
51
Idiopathic Intracranial Hypertension
• Gender and age distribution:
Idiopathic intracranial hypertension occurs most commonly among
women. The prevalence is approximately 1 case/100,000 women but
increases to 13 cases/100,000 women of ages 20 to 44 years who are 10%
above ideal body weight and 19 cases/100,000 women of ages 20 to 44 years
who are obese (20% above ideal body weight) (Durcan et al, 1988).
Men are affected less frequently. The incidence is 0.3 cases/100,000
men but increases to 1.5 cases/100,000 obese men(20% above ideal body
weight).Female-to-male ratios range from 4.3:1(Durcan et al, 1988) to
11.5:1(Mezaal and Saadah, 2005).
Idiopathic intracranial hypertension is predominantly a disease of
younger adults. In one major study, 59% of patients were in the third decade
of life at diagnosis, (Durcan et al, 1988) and mean ages at onset of
symptoms have been reported by others as 29 (Craig et al, 2001), 31 (Wall
and George , 1991), 35 (Galvin and Van Stavern, 2004) and 36 years
(Mezaal and Saadah, 2005).
Idiopathic intracranial hypertension may also be observed in the
pediatric population. A Canadian study of children demonstrated equal
incidence among boys and girls, of approximately 1 case/100,000
individuals (Baker et al, 1985).
8
52
Idiopathic Intracranial Hypertension
> Etiological factors and related conditions:
1. Genetic:
Isolated familial cases raise the possibility of a genetic component in
the disorder, but no linkage studies have been performed to date (Mokri,
2001).
2. Obesity:
The evidence linking IIH and obesity is conclusive. Even moderate
weight gain appears to be associated with IIH. Patients with Body Mass
Index (BMI) of 25-30 had an increased risk of IIH in a USA case-control
study, although higher categories of BMI were associated with
progressively greater risk of the condition (Daniels et al, 2007).
In the same study, 29% of patients reported no gain in weight and it is
important to note that IIH does occur in people who have normal or even
low body mass (Daniels et al, 2007).
Obesity is present in up to 94% of women and about 60% of men with
IIH (Wall and George, 1991), one of the proposed mechanisms relating
obesity to IIH are central obesity that raises cardiac filling pressures. This
rise in pressure leads to impeded venous return from the brain (due to the
valveless venous system that exists from the brain to the heart) with a
subsequent elevation in intracranial venous pressure. If not treated
appropriately, chronic interruption of the axoplasmic flow of the optic
nerves with ensuing papilledema due to this pressure may lead to
irreversible optic neuropathy (Daniels et al., 2007), also increased intraabdominal pressure that pushes the diaphragm superiorly and raises the
pleural pressure which then impede venous return from the brain leading to
9
53
Idiopathic Intracranial Hypertension
vascular engorgement and sustained increase of intracranial venous
pressure (Sugerman et al., 1997).
Obesity alone has been strongly associated with a chronic
inflammatory state, characterized by increased adipose-tissue production of
tumor necrosis factor-α and other proinflammatory “adipokines” associated
with increased expression of prothrombotic genes such as plasminogen
activator-inhibitor-1 and concentrations of lipoprotein (a) and estrogens,
each of which has the independent prothrombotic effect of increasing the
levels of several clotting factors (Trayhurn and Wood, 2004).
3. Vitamin A:
Excessive dietary intake of vitamin A has been associated with raised
intracranial pressure. Historical narratives of Polar Eskimos and their dogs
suffering from the clinical features of intracranial hypertension, including
headache and prostration, after ingesting large quantities of liver from polar
bears were later linked to the high levels of vitamin A in the organ
(Fishman, 2002).
Significantly heightened concentrations of retinol have been reported
in the CSF but not serum of patients with IIH compared with controls
(Tabassi et al., 2005).
4. Medications:
Case reports have implicated several drugs in intracranial hypertension.
Table (3) shows several drugs related to IIH. (Weese-Mayer et al., 2001)
10
54
Idiopathic Intracranial Hypertension
Table (3): Several drugs implicated in intracranial hypertension. (Weese-Mayer et
al; 2001)


Tetracyclines
Nitrofurantoin

Nalidixic acid

Sulfamethoxazole

Penicillin


Corticosteroid treatment and
withdrawal
NSAID in Bartter‟s syndrome

Mesalamine

Lithium carbonate

Amiodarone

Chlordecon

Ciclosporine
NSAID: non-steroidal anti-inflammatory drugs.
5. Menstrual Dysfunction :
A history of menstrual irregularities does appear to be more common in
IIH than in unaffected females. In one questionnaire study of 40 IIH
patients, a change in menstrual pattern just prior to diagnosis was more
frequently reported than in the reference period in 39 controls (Ireland et al.,
1990).
Larger studies have listed menstrual dysfunction amongst reported
symptoms, but there has been no published evidence of specific hormone
dysfunction to explain these findings and it is worth noting that obesity itself
is known to be associated with menstrual irregularities (Glueck et al., 2005).
11
55
Idiopathic Intracranial Hypertension
6. Pregnancy:
Pregnancy is occasionally associated with idiopathic intracranial
hypertension. This disorder can present at any stage of pregnancy
(Friedman and Jacobson, 2004).
A retrospective case control study and literature review concluded that
the apparent association with pregnancy reflects the age and gender of the
typical patient with IIH (Digre et al., 1984).
Further rigorous investigation has failed to show any statistically
significant relationship, with similar pregnancy histories amongst IIH
patients and matched controls (Ireland et al., 1990).
7. Polycystic Ovary Syndrome:
Polycystic ovary syndrome (PCOS) appears to occur with increased
frequency in IIH. In the study by Glueck et al.2005 37 (57%) of the 65
women with IIH were found to meet the diagnostic criteria for the syndrome.
Whilst this would appear to represent a much higher prevalence of PCOS
than that of the general population, the high levels of obesity in both IIH
cohorts and the lack of reliable data on the incidence of PCOS amongst a
similarly obese population make conclusions difficult to reach (Glueck et
al., 2005).
8. Sleep Disorders:
Sleep apnea syndrome (OSA) is also prevalent amongst an obese
population, but several papers have linked it with IIH (Purvin et al., 2000).
It remains unclear whether there is a disease association between OSA
and IIH, or if OSA plays a causative role in the condition, such that
12
56
Idiopathic Intracranial Hypertension
intracranial hypertension secondary to OSA is a separate clinical entity to
„true‟ IIH (Bruce et al. 2009).
9. Anaemia :
The diagnostic criteria for IIH specify severe iron deficiency anemia as a
condition that can masquerade as IIH (Biousse et al, 2003).
A retrospective consecutive case series at the Birmingham and Midland
Eye Centre, UK, between 2005 and 2007 of 107 new cases of IIH according
to strict diagnostic criteria found six instances of microcytic anaemia, with
haemoglobin levels below 10.2g/dl(gram/decilitre) (Mollan et al, 2009).
The prompt resolution of symptoms and improvement in visual function
upon correction of the haematological abnormality in all cases was highly
suggestive of an association between anaemia and raised intracranial
pressure. Testing patients who present with signs of IIH to exclude anaemia
is recommended (Mollan et al, 2009).
10. Co-morbid Conditions:
Systemic arterial hypertension has been reported as occurring in 14 to
32% of patients with IIH (Galvin and Van Stavern, 2004).
In one study, blood pressure was significantly higher amongst people
with IIH than matched controls (Ireland et al, 1990).
Other co-morbid conditions associated with IIH include diabetes
mellitus, thyroid disease, hypoparathyroidism, stroke, chronic migraine,
ulcerative colitis and systemic lupus erythematosus (Galvin and Van
Stavern, 2004).
There are published examples of apparent IIH occurring in patients
with a variety of other conditions, including hepatitis A (Thapa et al,
13
57
Idiopathic Intracranial Hypertension
2009a) and E (Thapa et al, 2009b), transplanted kidneys (Durcan et al,
1988) , leukaemia (Vartzelis et al, 2009) and the lysosomal storage disease
cystinosis (Dogulu et al, 2004).
Clinical features:
> Headache :
Headache has consistently been shown to be the most common
symptom of IIH, occurring in 68 to 98% of patients (Kesler and Gadoth,
2001).
It appears to be less common amongst children with the condition,
who may frequently present with other signs such as irritability or visual
failure (Lim et al, 2004).
A cohort study of 82 patients with IIH was performed and found 68%
meeting the diagnostic criteria for primary headache as defined by the
International Classification of Headache Disorders, ICHD-1. The headaches
were divided as tension-type in 30%, migraine without aura 20%, chronic
tension-type headache 10% and analgesia overuse in 8% (Friedman and
Rausch, 2002).
Isolated cases of cluster headache in association with IIH have also
been reported (Testa et al, 2008).
A further study showed ocular pain to be a much more predominant
feature in patients with IIH than controls (Daniels et al, 2007). Quite often,
14
58
Idiopathic Intracranial Hypertension
headache may be the only presenting symptom (Galvin and Van Stavern,
2004).
> Papilledema :
Disturbance of vision is the second most prevalent symptom of IIH.
Visual symptoms usually accompany headache, but may occur in isolation
(Galvin and Van Stavern, 2004).
Papilledema is almost a universal finding in IIH and its absence should
cause the diagnosis to be questioned (Mackenzie and Cioffi, 2008).
Papilledema, ranging from mild to severe, with or without hemorrhages,
is widely regarded as the hallmark of idiopathic intracranial hypertension.
Atypical cases are described in the adult literature where papilledema could
be asymmetrical, unilateral, or even absent (Wraige et al, 2002).
However, Idiopathic intracranial hypertension without papilledema is
a known condition in adults and usually presents with clinical features
resembling chronic daily headaches or migraine (Wraige et al, 2002).
A variety of symptoms are reported, including blurring secondary to
papilledema, double vision, field defects and short-lived visual abnormalities
such as Transient visual „obscurations (Kesler and Gadoth, 2001):
a. Visual Acuity(VA) :
The refracted visual acuity is often normal when tested in patients with
IIH. Reduced central visual acuity does occur, but review of the literature
suggests this to be the case in less than a quarter of patients at presentation
(Craig et al., 2001).
15
59
Idiopathic Intracranial Hypertension
b. Visual Field Defects:
Testing of visual fields by confrontation in patients with IIH may elicit
few abnormalities, but formal perimetry reveals that visual field defects are
often present and enlargement of the blind spot is nearly always seen. In
general, visual field abnormalities are one of the earliest indicators of
ophthalmic disease (Galvin and Van Stavern, 2004).
The visual field defects in papilloedema mirror those of other anterior
optic nerve pathologies, such as glaucoma and anterior ischaemic optic
neuropathy. Enlargement of the physiological blind spot is seen in most
cases of IIH, related to the effect of the swollen optic nerve head occupying
a larger area of retina (Figure 1). Often fields in IIH with blind spot
enlargement are categorised with normal fields, unless they encroach on
fixation, due to the benign and common nature of the finding. The locations
of other visual field defects in IIH reflect the retinal nerve fibre arrangement
and its relation to swollen areas of the optic disc. Of these „disc-related‟
defects, peripheral rim constriction appears to be the most common (Figure
2). Inferonasal steps are the next most common (Figure 3), then arcuate
scotoma, arch-shaped defects in the field of vision as well as nasal defects
(Galvin and Van Stavern, 2004).
Other less common defects include central, paracentral and
caecocentral scotomata, with temporal and altitudinal losses even less
frequently recorded (Wall and George, 1991). (Figure 4)
16
60
Idiopathic Intracranial Hypertension
Figure (1): Goldmann fields with minor enlargement of the blind spot as the only
abnormality (Galvin and Van Stavern, 2004)
Figure (2): Visual field (Goldmann perimetry) from the right eye of a 54 years female
with IIH showing marked constriction (Galvin and Van Stavern, 2004)
17
61
Idiopathic Intracranial Hypertension
-3 -10
-7 -6 -7
-12 0
-1 -8
-9
2
-5 -3 -4
-2
1
i
0 -3 -5
-2
-3
-3 -2
-4 -1
-i
-4 -5
-5 -5
-11 -5 -2 -4 -5
-3 -3
-9
-9 -3 0 -2 -3
-1
0
-6
-12 "11 -8 -4 -7
-2 -5
-12
-9 -8 -6 -2 -5
0
-3
-10
-15-13-2 -3
-4 -4
-5 -1
-2
-2
-3
-5 -2
-1
-3
0
1
0
-6
-4 -2 -5 -7
-9 -4 -4
-21 -21
-1
-13-11 0 0
-7 -2 -2
-2 -8
-19-19
Total
Pattern
Deviation
Deviation
- »
■'
3& - &I
8IISI
II
I» &
8 8
•
ȣ8
■ 8I
1
££
■ • • 8
£ ::
■8
■
■
£ • • ■ :
:
8
■
£ ■■ ■ S
■■ • •
£ " £ •
& • •
8
■I -I
:
: < 5%
£
& < 2% 8 <
1%
■ < 0.5%
Figure (3): Visual fields (Humphrey 24-2 automated static perimetry) from the right eye
of a woman with IIH. Generalised reduction in sensitivity with enlargement of the blind
spot and an inferonasal defect are shown. 1.7a: Visual thresholds as shown by greyscale
diagram and numerical results; 1.7b: Numeric and symbolic representations of the
calculated total and pattern response deviations from normal. (Galvin and Van Stavern,
2004)
18
62
Idiopathic Intracranial Hypertension
Figure (4): Examples of less common visual field defects in IIH (Wall and George,
1991) c. Transient visual
obscurations(TVOs):
Transient visual obscurations variously described as shadows, dark
patches or black spots in the field of vision, affecting one or both eyes
and resolving after a few seconds or minutes (Kesler and Gadoth,
2001).
19
63
Idiopathic Intracranial Hypertension
They may occur with changes in posture. Both the exact pathophysiology
and the prognostic significance of transient visual obscurations remain
unknown (Schirmer and Hedges, 2007). However it was said that the
underlying mechanism for visual obscurations appear to be transient
ischemia of the optic nerve head consequent to increased tissue pressure
(Sadun et al., 1984).
Additional Signs
It is a requirement of the diagnostic criteria for IIH that neurological
examination is normal except for the presence of signs reflecting generalised
intracranial hypertension and papilloedema (Friedman and Jacobson,
2002).
Unilateral or bilateral sixth cranial nerve palsies can therefore be
expected and have been specifically documented in some studies at rates of
17 to 33% (Mezaal and Saadah, 2005).
Abducens palsies are more likely to be unilateral and appear to be
more common amongst children (Johnston et al., 2007).
Other cranial nerve defects have been reported very rarely, in single
case reports, including facial and oculomotor palsies (Capobianco et al.,
1997).
20
64
Idiopathic Intracranial Hypertension
Investigations:
The diagnosis may be suspected on the basis of the history and
examination. To confirm the diagnosis, as well as excluding alternative
causes, several investigations are required as fundus examination &
magnetic resonance imaging (MRI); more investigations may be performed
if the history is not typical or the patient is more likely to have an alternative
problem : children, men, the elderly, or women who are not overweight
(Gonzalez et al., 2009). I.
Laboratory tests:
a) Blood tests:
Blood tests are done to rule out systemic lupus erythematosus or other
collagen-vascular disease, since these have been reported as underlying
conditions in some patients who present with idiopathic intracranial
hypertension (Nampoory et al., 1997).
Some authors advocate screening for anti-cardiolipin antibodies and
other procoagulant states in all patients with IIH who are either male or nonobese (Sussman et al., 1997).
b) CSF studies:
Examination of CSF pressure in patients with suspected IIH is
mandatory and lumbar puncture is a safe procedure in the fully conscious
patient with no focal neurological deficit and normal brain imaging, even in
the presence of papilledema (Bono et al., 2002).
Lumbar puncture is performed to measure the opening pressure
(levels above 25cmH2O is diagnostic), as well as to obtain CSF to exclude
alternative diagnoses. If the opening pressure is increased, CSF may be
21
65
Idiopathic Intracranial Hypertension
removed for relief. The CSF is examined for abnormal cells, glucose and
protein levels; in IIH, all are within normal limits (Friedman and Jacobson,
2004).
Occasionally, the pressure measurement may be normal despite very
suggestive symptoms. This may be attributable to the fact that CSF pressure
may fluctuate over the course of the day. If the suspicion remains high, it
may be necessary to perform more long-term monitoring of the intracranial
pressure by a pressure catheter (Friedman and Jacobson, 2004).
There are several issues surrounding the criteria of the measurement and
limits of the opening pressure. Whether the patient is supine, prone, or
sitting, one must be sure that the reference level for measurement is the level
of the left atrium. It is essential that the patient is as relaxed as possible and
time should be allowed for the pressure to stabilise. The knees and hips
should be in the extended position during pressure recording, since there is
evidence that a flexed posture as well as the Valsalva manoeuvre can elevate
the pressure. Spuriously high values can occur with Valsalva maneuver and
the hypoventilation associated with sedation (Neville and Egan, 2005).
II. Radiological Studies:
a) CT scan:
Computed tomography (CT) was the investigation of choice until it
was superseded by MRI. Computed tomography is adequate to rule out
larger tumors or lesions, but it is not as sensitive as MRI for meningeal
infiltration and/or dural venous sinus thrombosis. In IIH these scans may be
normal, although small or slit-like ventricles (Brodsky and Vaphiades,
1998).
22
66
Idiopathic Intracranial Hypertension
b) Brain Magnetic Resonance imaging:
Although there are no pathognomonic radiological signs in the
disorder but certain markers of raised intracranial pressure in patients with
idiopathic intracranial hypertension can be detected as follows:
• Flattening of the posterior sclera (80%):
In a retrospective study of imaging features that have been suggested
as typical for patients with IIH, only flattening of the posterior globe was
found statistically to be a reliable indicator of IIH, with a specificity of
100% and a sensitivity of 43.5% (Agid et al, 2006).
• Empty sella (70%):
The mechanism by which an empty sella develops in patients with
idiopathic intracranial hypertension is intrasellar herniation of CSF and
arachnoid membrane through an absent or open diaphragma sellae in
association with increased intracranial pressure. The pituitary gland is
flattened and distorted. The infundibulum is midline and extends down to
the floor of the sella turcica (Laura et al, 2005).
• Optic nerve sheath distension (ONSD):
The intraorbital part of the sheath, and particularly its retrobulbar
segment, can distend when ICP is elevated. MRI can be used to measure
precisely the diameter optic nerve and its surrounding sheath, by using a fatsuppressed T2-weighted sequence (Lam et al, 1997).
However, papilledema is a delayed consequence of chronic CSF
accumulation in the retrobulbar optic nerve dural sheath due to raised
23
67
Idiopathic Intracranial Hypertension
pressure in CSF in cranial cavity, and direct measurement of such CSF
accumulation may provide an earlier and more responsive measure of
intracranial hypertension. Optic nerve sheath distension could therefore
be an earlier, more reactive and more sensitive sign of raised ICP.
High-resolution MRI is accurate at measuring ONSD (Weigel et al,
2006).
• Prelaminar enhancement of optic nerves.
• Enhancement of the optic nerve distension of the perioptic
subarachnoid space.
• Intraocular protrusion of the prelaminar optic nerve.
• Vertical tortuosity of the orbital optic nerves. (Brodsky and
Vaphiades, 1998)
c) Magnetic Resonance venography (MRV):
Different MRV sequences offer the capability of investigating
cerebral sinovenous outflow from multiple orientations. Two-dimensional
time-offlight (2D-TOF) and three-dimensional phase-contrast (3D-PC)
techniques, that do not require contrast injections, have been widely used for
MRV imaging (Bono et al, 2003).
Sagittal T1-weighted images often provide excellent views of the
superior sagittal sinus, and these typically are included in routine MRI.
Extraluminal narrowing of the transverse sinuses may be a typical feature of
IIH as reported (Farb et al; 2003).
24
68
Idiopathic Intracranial Hypertension
Bilateral transverse sinus (TS) narrowing in patients with idiopathic intracranial
hypertension can be found regularly on MR imaging and may cause venous outflow
obstruction. Transverse sinus stenosis mostly consisted of a long smooth tapered narrowing
of the venous conduit. A minority had intraluminal filling defects, which were attributed to a
possible swelling of arachnoid granulation (Farb et al, 2003).
Thrombosis of the cerebral venous circulation can present with an identical clinical
picture to IIH (Biousse et al, 1999) .Thus to comply with recent diagnostic criteria, cerebral
venous sinus thrombosis must be excluded (Friedman and Jacobson, 2002).
■ Visual evoked potentials (VEP):
Clinical visual impairment in IIH is probably preceded by prolongation of VEP responses
and the latter may be evidence of optic nerve dysfunction due to demyelination (Kesler et al,
2009).
69
I.
Non-surgical management
This includes weight reduction, medical treatment and serial lumbar punctures.139 A.
Weight reduction
As obesity and/or recent weight gain are the main identifiable IIH risk factors in most
patients, a defined weight loss program should be initiated regardless of disease severity.
Observation without medical or surgical intervention may be indicated in an asymptomatic
patient who presents with papilledema and understands the importance of clinical monitoring
for progression. The precise relationship between weight gain or obesity and raised ICP is
not clear, but the benefits of weight reduction have been demonstrated repeatedly. In a study
of 25 obese women, weight reduction was associated with reduction of headaches,
papilledema, and ICP.141 In addition, in individuals whose IIH is in remission, prevention of
weight fluctuation has been shown to be critical in prevention of recurrence.142 Studies have
demonstrated that loss of approximately 6% of body weight is associated with a reduction in
papilledema and discontinuation of systemic treatment.5 To most effectively assist a patient
in weight loss, the help of a registered dietician or nutritionist should be enlisted. If weight
loss through diet and exercise fails, bariatric surgery has been shown to positively benefit
IIH, although this is clearly more invasive and carries risks of anastomotic leaks, small
bowel obstruction, mal-absorption, and gastrointestinal bleeding.
B. Serial lumbar punctures
Assuming a normal rate of CSF production in IIH (and there is no evidence to the
contrary), the theoretical objection to serial lumbar punctures as treatment is that volumes
around 20-30 ml will be restored in a very short time so, unless some other factor is
operative, there will not be a sustained reduction in CSF pressure. It has been suggested that
repeated punctures may create a leak, even a fistula, at the puncture site(s) which can
produce the required sustained effect. Such a leak must be considered as unpredictable, both
in its occurrence and its presumed effect. There is also the possibility that reduction of CSF
pressure by drainage might favourably influence a cycle of events involving venous sinus
collapse. On present evidence, the most that can be said is that a small percentage of cases of
IIH do show resolution on treatment with repeated lumbar punctures, but how much this is
due to the punctures themselves is an unresolved issue.
70
Further, the treatment is distressing to the patients so, given the other options available, the
method is no longer applicable. If sustained drainage of CSF is thought to be desirable, it
should more effectively be achieved by continuous drainage via any mean of chronic CSF
diversion.139
C. Medical treatment
Medical treatment is indicated in the setting of good vision when a patient’s primary
symptom is headache. It includes analgesics for symptomatic relief of headache, Carbonic
anhydrase enzyme inhibitor (Diamox©), steroids and others.139
i.
Analgesics
Symptomatic therapy is often necessary even in the setting of preventative medication use
in order to treat acute "break-through" headaches. The use of acute symptomatic therapy
should be limited to no more than 2 days per week, as more frequent use raises the risk of
medication overuse headache (MOH). Standard acute therapies can be used in conjunction
with preventative therapy. Non-steroidal anti-inflammatory drugs (NSAIDs) such as
naproxen and indomethacin can be used for both migraine and tension-type headache. There
is some evidence that ind omethacin (Dosage: Initially 50 mg IV, followed by oral
maintenance dose of 75 mg/day) also helps to lower ICP, making it a good choice in this
population.
The ICP-lowering effects of indomethacin can be explained best by vasoconstriction and a
consecutive reduction of the cerebral blood flow (CBF). After IV administration of
indomethacin there is a significant increase in the arterio-venous oxygen difference. Several
studies have shown that indomethacin does not cause cerebral ischemia, because the cerebral
metabolic rate of oxygen or the net production of lactate does not significantly change after
IV administration. In healthy volunteers auto-regulation is preserved, because the
vasoconstrictive effects of indomethacin are still influenced by hypoxemia and hypercapnia.
Indomethacin does not influence the effects of other standard therapies for ICP control, but it
does cause a rebound increase in ICP after drug discontinuation.143
ii.
Carbonic anhydrase enzyme inhibitors (CAIs)
Acetazolamide clearly has a role in the management of IIH and might legitimately be
regarded as the first line of medical treatment. Although, as with other methods of treatment
for IIH, there is no definitive study of the use of the drug, the impression from available
reports is that it is likely to be effective in approximately 20-40% of cases with a greater
71 particularly if there is a causative factor for
chance of success in children and adult males,
the IIH which can be withdrawn or corrected. Acetazolamide is generally well tolerated with
72
a low incidence of side effects and is suitable for prolonged use if the clinical situation so
dictates. Some patients are intolerant of acetazolamide, however, and in all cases regular
assessment of blood electrolyte levels is advisable.139 Acetazolamide (Diamox©) and
Methazolamide (Neptazane©) inhibit carbonic anhydrase in the choroid plexus, ostensibly
decreasing CSF production. They also act as mild diuretics. Acetazolamide in adult patients
is usually started at 1 g daily (250 mg QID or 500 mg BID); with a maximum recommended
daily dose of 4 g. Side‑effects include paraesthesia, lethargy, and altered taste and may limit
dosage.144 Whether it is better to use acetazolamide alone or in combination with other
treatments such as lumbar punctures, steroids, other diuretics or even cardiac glycosides is an
unresolved question. Topiramate is an alternative carbonic anhydrase inhibitor which has
recently been tried in some patients with IIH. It is approved for the treatment of epilepsy and
migraine prophylaxis and also causes anorexia which has merit for many patients with
IIH.139
iii.
Diuretics
Although non‑CAI diuretics (i.e. furosemide, chlorthalidone, and spironolactone) have
been used in the treatment of IIH, their efficacy in reducing ICP is unclear. Hypokalaemia
may occur with any of these agents, and blood electrolytes should be monitored.144
A very little can be said about the use of diuretics other than acetazolamide in the treatment
of IIH. There are clearly some cases in which they will be successful, and resolution has
been reported with ‘standard’ diuretics, particularly chlorothiazide, frusemide and with
osmotic diuretics such as glycerol and urea. There is, however, no evidence from which to
draw any conclusions about their relative merits, either with respect to each other or with
respect to other treatment methods.139
iv.
Steroids
Beginning with the report by Paterson et al. in 1961, steroids (prednisone, prednisolone,
methylprednisolone, betamethasone, and dexamethasone) were, for a time, the first choice
treatment for IIH in a number of centres. There was also, during this time, an increasing
awareness of the complicated relationship existing between IIH and steroids since not only
did steroids appear effective in treatment but also there were reports of cases of IIH
occurring in patients being treated with steroids for other conditions, particularly during
staged withdrawal of the agent.145
Johnston et al. reported 7 cases of IIH treated with steroids and documented CSF pressure
before treatment and 3months after the start of the therapy. All patients had their intracranial
73
pressure evaluated by continuous monitoring before, during, and after treatment.
74
All seven patients were completely free of symptoms and signs at 3 months. Despite this,
the CSF pressures, which were essentially unchanged at 1 week, were still above normal at 3
months (Fig.29), although there was a significant reduction (pre-treatment mean 27.2 mmHg,
SD 5.7; 1-week mean 27.3 mmHg, SD 4.0; 3-month mean 21.2 mmHg, SD 6.5).139
Before treatment
1 month after
VV^%A^Vv^^Av- 'yifl^/^hf^
1
1
20
1
40
20
40
Time (min)
Figure 29: CSF pressures of one of the 7 patients before and one month after treatment course of
steroids.72
In summary, there is undoubtedly a moderate recurrence rate for IIH after steroid treatment
(probably between 10 and 20%), and a definite incidence of complications some of which
are of a serious nature. Steroids are probably more effective in combination with either
acetazolamide or serial lumbar punctures, or both, although there are no properly conducted
studies to support this impression. In the uncommon cases of IIH occurring during
withdrawal of steroids being administered for an unrelated condition, restoration of a higher
dose of steroids followed by a more gradual withdrawal is the primary treatment but this may
have to be supplemented by another agent. Currently, however, the use of steroids is limited
to cases of rapidly deteriorating vision including cases of cerebral venous thrombosis in
combination with CSF drainage.139
v. Others
There are several forms of medical treatment other than those already considered which
have been used in small numbers of cases of IIH. These include cardiac glycosides,
specifically digoxin, which has been shown experimentally to effect a 61-78% reduction in
CSF production, an effect more pronounced than that of acetazolamide.
This drug is it effective as a single agent but ineffective when used in conjunction with
75
diuretics. However, it has been disappointing in its very limited clinical use.146
76
There is also a report of the use of hyperbaric oxygen (HBO) in the treatment
of IIH in eight cases. Each patient underwent HBO with 100% oxygen at 2
atmospheres absolute a day for 15 days. In all patients a gradual disappearance
of signs and symptoms of elevated intracranial pressure was observed. No
lasting effect of treatment was seen after concluding therapy. The effect of HBO
in the treatment of IIH has not yet been clarified, but the results can encourage
further experience and studies.144
25
77
78
LUMBO-PERITONEAL SHUNTING
INDICATION:
progressive visual failure from papilledema due to increased intracranial
pressure and intractable generalized headaches. In this small subset patients
who do not respond to conventional medical therapy.
CONTRAINDICATIONS:
The shunting procedure requires the introduction of a large 14-gauge Tuohy
needle into the lumbar subarachnoid space. This may not be feasible in some
clinical situations. Patients with advanced lumbar degenerative arthropathy with
marked spinal stenosis have a very narrow spinal canal with crowding of cauda
equina roots, and a spinal tap or the satisfactory advancement of the lumbar
catheter may not be technically possible. Patients with an advanced degree of
congenital kyphoscoliosis with rotational deformities may also present a similar
problem. Achondroplastic dwarfs tend to have an extreme degree of narrowing
of the spinal canal, and in such individuals a ventriculoperitoneal shunt may be
the better alternative. Patients who have undergone multiple previous lumbar
laminectomies for disc disease with documented evidence of adhesive
arachnoiditis or with radiologic evidence of an extensive posterior midline fusion
of the lumbar spine are not suitable candidates for lumbar-peritoneal shunting.
Very small infants will not accommodate the 14-gauge needle that is required
for the introduction of the catheter.
Patients who have congenital anomalies in the lum-bosacral region, such as
meningomyelocele,
tethered
cord
syndrome,
lipomeningocele,
diastematomyelia, etc., are better treated by ventriculoperitoneal shunting.
Patients with a Chiari malformation or aqueductal stenosis with hydrocephalus
are also best treated by ventriculoperitoneal shunting. Patients with infection or
skin breakdown in the lumbar area, with chronic infection from any cause, or
with vertebral osteomyelitis or discitis are not suitable candidates for lumbarperitoneal shunting
DESCRIPTION OF THE SHUNT SYSTEM:
The main components of the lumbar-peritoneal shunt system are a lumbar
catheter, a peritoneal catheter, a valve unit, a “stepdown” connector between
the lumbar catheter and the valve unit, a straight connector between the valve
unit and the peritoneal catheter, and a suture clamp.
The Valve Unit :
79
The valve unit (Fig. 1, inset) provides controlled drain-age of the cerebrospinal
fluid from the lumbar sub-arachnoid space into the peritoneal cavity while
maintaining the intracranial pressure in the physiologic range. The valve has a
unique bimodal design to compensate for varying hydrostatic pressures in the
recumbent and upright positions. On the inlet side is the lower pressure
mechanism consisting of a spring actuated ball-in-cone valve. The tension in the
spring determines the valve opening pressure. On the outlet side is the higher
pressure, gravity actuated mechanism consisting generally of three freely rolling
steel balls. The combined weight of the balls determines the opening pressure.
Figure 1. The lumbar-peritoneal shunt
assembly in place. The valve unit is
shown enlarged at the top (inset).
In
the
horizontal position,
only
the
lower
pressure,
spring
actuated,
ball-incone valve
is functional. The
spinal fluid, after it escapes out of the valve, simply flows by the steel spheres
which are free to move and do not block the entry site into the high pressure
mechanism. As the patient assumes an upright position, however, the steel balls
gravitate down and block the entry site into the mechanism. For the fluid to flow
now, it has to lift up the steel balls. In the upright position, both the spring
actuated and gravity actuated mechanisms are functional; thus in the upright
position, spinal fluid flow remains constant despite the higher hydrostatic
pressure.
The low and high pressure valves are housed in a clear silicone elastomer
casing. The inlet tubing into the valve is clear and the outlet tubing is opaque. A
color-coded band at the lower waist of the silicone casing indicates the pressure
ranges of the horizontal and vertical valves (Table 1.)
80
An appropriate range of valve pressures should be chosen based on the
ventricular size and the height of the patient (Table 1). The range of opening
pressure for the horizontal valve is chosen based on the ventricular size. A lower
opening pressure range (50-80 mm H2O) should be chosen for patients with
extreme ventricular enlargement and a standard opening pressure range (85125 mm H2O) for patients with moderate ventricular enlargement. The opening
pressure of the vertical valve is chosen according to the patient’s height. Tall
adults with moderate ventricular enlargement will require valves with a higher
opening pressure range (325-445 mm H2O). Average adults or tall children with
moderate ventricular enlargement will require a standard opening pressure
range (265-365 mm H2O).
Lumbar Catheter
The lumbar catheter is a narrow radiopaque silicone catheter with multiple
small perforations at its distal end. The distal end is inserted into the lumbar
subarachnoid space through a Tuohy needle and the proximal end is connected
to the inlet side of the valve unit.
Peritoneal Catheter
The peritoneal catheter is of larger diameter than the lumbar catheter. It is
also made of radiopaque silicone elastomer. Its proximal end is connected to the
outlet side of the valve unit using a straight connector. The distal end has
several staggered rows of slits which provide multiple routes of drainage but do
not function as valves.
“Stepdown” Connector
The stainless steel stepdown connector is used to attach the lumbar catheter
to the inlet side of the valve unit. The smaller side connects to the catheter and
the larger side connects to the valve unit.
Straight Connector
The stainless steel straight connector is used to attach the peritoneal catheter
to the outlet side of the valve unit.
Suture Clamp
A butterfly suture clamp made of silicone is used to anchor the lumbar
catheter to the lumbo-dorsal fascia near the entry site of the catheter to
prevent migration of the catheter during
movements of the back (Fig. 3E).
81
PREOPERATIVE PREPARATION:
A diagnostic workup should include brain imaging with an MRI or CT study to
confirm the clinical diagnosis and to rule out obstruction within the ventricular
pathways. A plain roentgenogram of the lumbar spine in the anteroposterior
projection will rule out any local abnormalities that will contraindicate a lumbar
puncture. In a patient who has undergone multiple previous abdominal
procedures with significant abdominal adhesions, the help of a general surgeon
may be sought to assist in the laparotomy component of the procedure. If the
patient has had a recent diagnostic or therapeutic lumbar puncture, the
operation should be delayed for at least three to five days so that during surgery
the lumbar catheter is more likely to enter the subarachnoid space rather than
the subdural space. If the clinical situation permits, it is best to readmit the
patient a week to 10 days after the tap for the definitive surgical procedure.
OPERATIVE TECHNIQUE :
Anesthetic Considerations and Patient Positioning:
I always use general anesthesia for this procedure. Good muscle relaxation
will help during the laparotomy.
The operation is always done in the lateral decubitus position (Fig. 2A). It can
be either the right or the left lateral decubitus position depending on the
surgeon’s preference. I generally use the right lateral decubitus position with
the patient’s left side up. The patient is rolled over a soft egg crate mattress in
the lateral decubitus position with the hip and knee flexed on the down side and
extended on the up side. All the pressure points are additionally padded,
especially those under the greater trochanter and the right arm. A rolled sheet is
placed under the axilla to prevent compression of the axillary artery and vein.
The free left arm is held over in a suspended arm rest as is generally used in
thoracotomy procedures. The patient may lay over an inflatable bean bag
mattress which helps to retain the lateral decubitus position throughout the
procedure. The head should be supported on sheets or pillows to maintain its
neutral position, in line with the spine. The chest and the knee are flexed to
maximize the interspinous space but there should be sufficient room in front for
laparotomy access. The back, flank, and abdomen are shaved, prepared, and
draped. In patients in whom the CSF pressure is low, the operating table may be
tilted into a head up position to promote good flow of CSF.
82
Figure 2. A, the lateral decubitus position used for lumbar-peritoneal shunting. B, lumbar
puncture with a Tuohy needle. C, rotation of the needle by 90° to direct the bevel of the needle
cephalad.
Checking the Valve for Patency and One-way
Flow:
Before implantation of the valve unit, the
valve
patency and one-way flow mechanism should
be
checked, as follows.
Patency:
The valve unit is temporarily connected to
the
lumbar and peritoneal catheters. The inlet
(lumbar) tubing is submerged in a sterile saline
solution. A syringe is attached to the distal (peritoneal) end of the tubing
through a blunt 18-gauge needle. Saline is slowly aspirated through the system,
purging out all of the air. The syringe is then disconnected, and the distal end is
allowed to hang freely. Patency is proven if saline drips from the distal end.
One-way Flow Mechanism:
After the valve unit and the catheters have been filled with saline in the
manner described above, the valve is held vertically (with the arrow pointing
down) and the distal end of the peritoneal catheter is elevated above the valve
unit. Absence of fluid return through the proximal tubing for 80 seconds
confirms an intact one-way flow mechanism.
Introduction of the Lumbar Catheter:
I generally do not make a lumbar incision before the insertion of the needle.
In the unlikely event that the lumbar puncture is not successful, then one may
have to go to a space higher or lower. Ordinarily, the lumbar puncture is
performed at the L3-L4 or L4-L5 space. Standard anatomical landmarks are used
(Fig. 2B). The top of the iliaccrest83 generally corresponds to the L4-L5
interspinous space. One should be cognizant of the fact that in the lateral
decubitus position the spinous processes do not lie exactly in the midline
between the paraspinal muscle masses. They tend to be at a slightly upper
(lateral) level. In difficult cases it may be necessary to use fluoroscopy briefly to
identify the appropriate interspace and the mid-line with a marker.
A 14-gauge, thin-wall Tuohy needle is then passed parallel to the plane of the
floor and directed 10 to 15° cephalad. The needle should be advanced slowly
and cautiously because the goal is to enter the subarachnoid space in a single
pass. The bevel of the needle is directed horizontally until the dura is
penetrated. In many instances, a pop may be felt as the dura is penetrated. The
needle is advanced in small increments and the stylet is removed periodically to
ascertain whether the subarachnoid space has been entered. This careful
maneuver prevents going past the ventral dura and thus hitting the ventral dural
venous plexus. Once the arachnoid has been pierced and the stylet has been
removed, a gush of spinal fluid escapes because of the size of the needle.
In some instances the fluid flows well initially but then stops abruptly because
of the tamponading of the tip of the needle by a nerve root. In such instances,
gently turning the needle by 30 to 50° will change the direction of the distal
aperture of the needle and thus will facilitate better flow. If one is in doubt
whether the subarachnoid space has been penetrated properly, a small quantity
of a water-soluble contrast agent may be injected through the needle and an
anteroposterior roentgenogram taken with a lateral beam which will show the
contrast agent in the subarachnoid space.
After the placement of the needle into the lumbar subarachnoid space, the
bevel of the needle is turned either cephalad or caudad to direct the catheter
(Fig. 2C). The stylet is removed and the thin radiopaque lumbar catheter, which
has multiple perforations at the end, is inserted through the needle into the
lumbar subarachnoid space (Fig. 3A). The insertion is generally easy although
the catheter typically hesitates a bit as it maneuvers the curve at the tip of the
needle before passing on with relative ease. In exceptional situations, a
guidewire can be used to stiffen the catheter and direct it into the lumbar
subarach-noid space. In no circumstance should the catheter be withdrawn
through the needle because the sharp end of the needle may shear the
catheter. If the catheter must be withdrawn for any reason then the needle
should be withdrawn along with it. It is not necessary to insert more than 8 or
10 cm of the catheter tube into the lumbar subarachnoid space. In fact, a
catheter longer than this may tend to irritate the cauda equina roots because of
its entanglement within the roots. If the84CSF is bloody, the lumbar catheter must
not be inserted until the fluid is completely clear. During the insertion of the
catheter it is best to leave its other end open to monitor free flow which will
ensure that it is not being kinked.
When the catheter has been passed to the desired length, a lumbar skin
incision is made for 1 cm on either side of the needle (Fig. 3B). I prefer to make
the incision before the needle is withdrawn because incising the skin after
needle withdrawal carries the risk of nicking into the lumbar catheter. The
needle is then withdrawn over the catheter; the surgeon should hold the
catheter at the skin puncture so it does not get pulled out. A small hemostat
protected with rubber sleeves is used to clamp the tip of the catheter. Near the
entry site of the lumbar catheter into the spine, the catheter is anchored to the
lumbodorsal fascia with a butterfly suture clamp (Fig. 3E).
85
Figure 3. A, insertion of the lumbar catheter through the Tuohy needle. B, a skin incision is made on either side of the Tuohy needle. The presence of the needle
prevents the catheter from being nicked by the knifeblade. C, D, the lumbar catheter is brought to a flank incision with a subcutaneous tunneler. E, the lumbar
catheter is anchored to the lumbodorsal fascia with a butterfly suture clamp (enlarged view).
Flank Dissection
A horizontal 5 cm flank incision is made midway between the costal margin
and the top of the iliac crest. The
86 incision is deepened through the
subcutaneous fatty layer until the fascia covering the external oblique muscle is
exposed. Self-retaining retractors are inserted. Using a tissue tunneler, the
lumbar catheter is brought into the flank wound from the lumbar area (Fig. 3C
and D). The lumbar catheter is again clamped.
Minilaparotomy
A horizontal incision is made about 2-4 cm above the umbilical level,
extending from the midline to the lateral border of the rectus abdominis muscle
(Fig. 4A). The skin, subcutaneous tissue, and anterior rectus sheath are incised
horizontally, and self-retaining retractors are inserted (Fig. 4B). Subcutaneous
bleeders are coagulated. The rectus abdominis muscle is split using a hemostat
or any other appropriate blunt instrument (Fig. 4C). The posterior rectus sheath
is exposed and it is grasped with hemostats and lifted up. Using a No. 15 blade
knife or blunt-tipped scissors, it is incised. I make sure that the peritoneum is
also incised. Fatty tissue extrudes out of the opening (Fig. 4D). Make sure that
this represents omentum and not preperitoneal fat. If the peritoneal cavity has
indeed been entered, one should be able to insert almost three-fourths the
length of a blunt Freer elevator (about 5 inches) easily and without any
resistance. The distal end of the peritoneal catheter (which has a square tip) is
inserted into the peritoneal cavity using a bayonet forceps, and the catheter is
directed toward the subhepatic space (Fig. 4E).
The peritoneal catheter has two or three slits near the end. These slits are
designed to open in case the tip of the catheter gets plugged. These slits do not
function as slit valves but merely as additional ports. The catheter then is
tunneled through the subcutaneous space and brought into the flank wound
(Fig. 5A).
Final Shunt Assembly
The valve unit should be filled with saline to remove the air pocket from the
valve, through a blunt needle attached to the inlet side (clear) tubing. The
lumbar tubing is trimmed to the desired length and connected to the inlet side
of the valve unit with the stepdown connector. The connection is secured with
3-0 silk ligatures. The clamp on the lumbar catheter is released. If the valve is
now held in a horizontal position, the CSF will flow out of the outlet side of the
valve. The lumbar catheter is then reclamped. The free end of the peritoneal
catheter is brought into the flank wound and excess length is cut off (Fig. 5B).
The peritoneal catheter is connected to the outlet side (opaque tubing) of the
valve unit using a straight connector (Fig. 5C). For optimal functioning of the
valve unit, it should be oriented properly. A properly oriented valve unit will
have its long axis parallel to the long axis
87 of the trunk of the patient (Fig. 5D).
The arrow on the inlet valve should point toward the patient’s feet. The valve is
secured to the fascia overlying the external oblique muscle by passing fine
Nurolon sutures through the four holes in the valve housing (Fig. 5D). The shunt
assembly is now complete. Lumbar, abdominal, and flank wounds are closed in
layers using absorbable sutures. Subcuticular skin sutures are used.
88
Figure 4.
incision
A, the skin
used for the
minilaparotomy. B, incision of the anterior rectus sheath. C, longitudinal blunt separation of the rectus
abdominis fibers. D, incision of the posterior rectus sheath and the peritoneum; a portion of the omentum
extrudes out. E, insertion of the distal catheter into the peritoneal cavity.
Figure 5. A, a tunneler is used to bring the peritoneal catheter to the flank incision. B, the peritoneal catheter is
brought into the flank wound (note the clear tubing on the inlet side of the valve unit and the opaque tubing on the
outlet side). C, the peritoneal catheter is attached to the valve unit. D, the final orientation of the valve unit after the
lumbar and peritoneal catheters have been attached to it. The valve unit is being anchored to the fascia over the
external oblique muscle through the four holes in the valve unit.
POSTOPERATIVE MANAGEMENT
The patient is maintained on intravenous fluids for about 24 hours until active
bowel sounds are heard and bowel activity is established. The patient is then
started on clear liquids, progressing to a regular diet. Adequate narcotic
analgesics are administered. To ensure that the patient gets acclimatized to the
shunt, the head of the bed is gradually elevated in increments over a period of
24 hours and the patient is generally allowed to sit on the side of the bed by 48
hours. The patient can then get out of89bed in a chair for a few hours at a time
and is allowed to ambulate on the third or fourth day. This cautious
management facilitates the patient getting used to the new CSF dynamics.
Usually the patient is ready to be discharged on the fifth postoperative day.
A follow-up CT or MRI study is obtained one month postoperatively which will
confirm normalization of ventricular enlargement. Patients with pseudotumor
cerebri are monitored serially with visual field testing, visual acuity
measurements, and fundus photography.
COMPLICATIONS OF SURGERY
Like any shunt, the lumbar-peritoneal shunt is susceptible to infections. The
incidence of infection is low because no component of the shunt is in the venous
system. If shunt blockage is suspected, it has to be confirmed by a radionuclide
study. The radionuclide is injected into the lumbar subarachnoid space and the
flow of the nuclide through the shunt into the peritoneal cavity is monitored. If
the shunt is patent, the radionuclide should escape into the peritoneal cavity
within minutes after injection.
If it is not functioning, the shunt will need to be replaced. About 1 to 2% of the
patients present with manifestations of cauda equina root irritation. In most
instances this is transient and resolves with time. If this persists, the lumbar
catheter will need to be replaced. Headaches are uncommon but may occur if a
proper valve with appropriate pressure has not been chosen. Lack of precipitous
drainage of CSF in the upright position, attributable to the unique shunt design,
has kept the incidence of subdural hematoma very low. Even if a subdural
hematoma occurs, it is seldom of the massive degree that is seen with the single
pressure opening device. Migration of the catheter from the spinal canal should
not occur if the lumbar catheter has been properly anchored to the lumbar
fascia with
90
ii. Optic nerve sheath decompression (ONSD)
ONSD has a high success rate in improving or stabilizing visual function in IIH, at least in
the short to medium term. It is less effective in dealing with headache, and over time a
significant number of patients will require further treatment, whether it be repeat ONSD,
medical treatment or other surgical measures, either to control headache or to deal with later
visual deterioration.139
The mechanism by which ONSD works has not been clarified, but several theories have
been suggested. Keltner suggests that it may provide a filtering effect, with a subsequent
decrease in the local CSF pressure, improvement of the peri-papillary circulation, or produce
a generalized decrease in ICP.15 According to another hypothesis, the scarring of the
arachnoid by the procedure itself may protect the nerve head from elevated CSF pressure.31
Technically, ONSD is performed by uncovering the optic nerve sheath through a lateral
orbitotomy or through a medial approach via a trans-conjunctival incision. Multiple linear
incisions are made or a window is cut into the anterior dural that covers the optic nerve
sheath, creating a CSF drainage outlet.151
There is a moderate complication rate for the procedure although the great majority of
complications are either minor or transient or both. The overall complication rate ranges
from 4.8% to 45%, Complications includes148:
• Ocular motility disorders (e.g. temporary horizontal motility disorder caused by disinsertion of the medial rectus muscle or combined third and sixth nerve palsies).
• Chemosis.
• Chorio-retinal scar from excessive traction on the globe.
• Orbital haemorrhage.
• Trauma to the optic nerve.
• Micro-hyphaemas.
• Orbital apex syndrome.
• Optic nerve cyst formation with proptosis, pain and vision loss.
• Streptococcal corneal ulcer.
• Dacryocystitis.
• Deterioration of visual function, transient blindness, choroidal infarction.
• Central or branch retinal artery occlusion.
91
In the majority of patients, post-ONSD vision stabilizes or improves but its long-term
efficacy remains in question. Also there is evidence that CSF pressure may remain high
despite clinical improvement. A reoperation can be performed, a shunting procedure is
recommended in these cases.139
iii.
Venous sinus endovascular stenting
Transverse cerebral venous sinus stenosis is a common finding in patients with IIH. Their
origin and functional significance remains controversial. It has been postulated that patients
with increased ICP develop the stenosis due to external compression of the venous sinus.
Indeed, the stenosis sometimes resolves when ICP is reduced by lumbar puncture or
shunting. Modelling studies have suggested that stenting of these stenosis might reduce
cerebral venous pressure, leading to increased CSF absorption, reduced ICP, and improved
symptoms and signs, even if the stenosis are caused by increased ICP. 152 Supporting this
hypothesis are the findings of case studies and series, in which patients have undergone
endovascular stenting of this stenosis, with subsequent normalization of ICP and resolution
of symptoms and signs.20;24;103
It is highly controversial whether venous sinus narrowing is the cause or the result of
elevated intracranial pressure. Based on the frequent findings in MRI venography of
narrowed transverse sinuses, endovascular stenting of the venous sinuses has been recently
advocated by some authors.20
Higgins et al was the first to report on a 30 year old patient with refractory IIH, papilledema
and bilateral transverse sinus stenosis found on an MRV that was successfully treated with
dilation of one of the sinuses with a stent, thus reducing the pressure gradient with dramatic
symptomatic improvement.21
With the patient under general anaesthesia, a percutaneous venoplasty is performed. A stent
is then deployed at the site of the previous stenosis (Fig.34). Manometry is often performed
following deployment of the stent, to confirm that any pressure gradient across the stenosis
has been alleviated. Long-term antiplatelet treatment is required to prevent in-stent
thrombosis.
Contraindications of this procedure have not been clearly defined, but might include active
infection and use of anticoagulants.
Common complications include transient frontal or temporal headache, due to stretching of
the meninges covering the transverse sinus. Transient hearing loss has also been reported.
There are reports of more serious complications, including in-stent thrombosis, subdural
haemorrhage, and death in one patient.20;137 Few patients develop recurrent stenosis proximal to
the stent because of the triangular anatomy of 92
the venous sinus which leads to collapse of
the segment immediately proximal to the cylindrical stent, with recurrent symptoms and
signs of increased ICP.24;103
V, ^>*\
Figure 34: IIH in a 32-year-old, non-obese woman. (Left): MRV showing marked narrowing of the right transverse
sinus. (Centre): Retrograde sinography and manometry showing focal obstruction of the right transverse sinus and
associated intraluminal pressure gradient. (Right): Repeat retrograde sinography and manometry post-dilatation
showing improvement in flow and pressure gradient. All pressures in
mmHg.22
Figure 35: A case of a 9-year-old boy with a large dominant right transverse sinus. (a) Lateral DRCV demonstrating
the significant right transverse sinus obstruction. There was a gradient of 11 mmHg across the obstruction. (b) Image
during stent deployment. (c) Lateral DRCV of right transverse sinus with the stent fully deployed showing abolition
93
of the obstruction.137
94
Although the promising initial results of long term efficiency of the procedure still needs to
be proven, further investigation is still warranted to prove the procedure as a useful treatment
technique
It is still unclear if primary treatment of the observed stenosis benefits patients with IIH.
This should be no surprise, as it is not certain whether the stenosis is the cause or the result
of IIH.148
iv. Sub-temporal decompression (STD)
The first neurosurgical technique to treat IIH patients, by a sub temporal decompression,
was performed by Dandy in 1937. Dandy performed a unilateral sub temporal craniectomy
with excellent initial results in alleviating headaches and preventing visual loss. The longterm efficacy of the procedure was uncertain, since a high rate of morbidity and
complications were reported, including seizures, infections, focal brain damage, cosmetic
disfigurement, intracranial hematomas, and further visual deterioration.34
In summary, it does appear that STD still has a place in the management of IIH, albeit a
somewhat limited one. Thus, it might be employed in patients who have proceeded to one of
the other surgical treatments (optic nerve sheath decompression or CSF shunting) and have
continuing problems, either failure to control the disease (ONSD), or recurrent malfunction,
or other complications (shunting). If, in such refractory cases, STD is decided upon, it should
probably be bilateral and large with a careful technique including splitting of the dural layers
to form over-riding flaps, or scoring the dura with multiple lines without penetrating it, to
protect the cortical surface.139
Outcomes
The natural history of IIH is unknown. In some cases, it is a self-limited condition, while in
others ICP may remain elevated for many years even if systemic and visual symptoms
resolve. In some patients, the process may last from months to years. Individuals with mild
to moderate visual loss tend to recover vision following medical therapy. Papilledema
usually resolves after a few weeks or months, but many patients are left with some residual
disc elevation, especially nasally. Severe visual impairment may be a serious and permanent
complication of IIH.
IIH produces significant visual impairment in approximately 25% of patients. The risk of
visual loss in the paediatric IIH population is similar to that of adults. Recurrent symptoms
have been reported in 8 to 37% of patients, years after being diagnosed.4
Visual deterioration in IIH patients is usually gradual, but in cases of fulminant
papilledema, blindness may appear rather quickly. In Corbett et al. follow up study of 5 - 41
95
years after the initial diagnosis of 57 patients, revealed severe visual impairment in 14
patients (24.6%)4 In Kesler et al. experience, recurrence was frequently associated with
weight gain. The long term prognosis and visual outcome of 54 patients with IIH was
observed over a period of 6.2 years. The results showed that recurrences occurred in almost
40% of the cases. None of these exacerbations occurred during the first 10 months, and none
occurred while the patients continued treatment.33
There are several aspects pertaining to outcome which merit separate and particular
consideration. These aspects include the outcome for visual function, psychological sequelae
and persistence elevation of CSF pressure.153
♦ Outcome for visual function
A significant proportion of IIH patients will be left with permanent impairment of vision
involving visual acuity, visual field or both. While there is quite considerable variation in the
reported incidence of such impairment, it is probably of the order of 10-20% with current
methods of management and evaluation.
In general, the likelihood of such loss is related to the chronicity and severity of the
intracranial hypertension, this causing prolonged disturbance of axoplasmic flow in the optic
nerves with secondary vascular changes which may themselves be irreversible, or which may
lead to irreversible changes.153
♦ Psychological and psychiatric sequelae
There is the largely unexamined issue of whether there are significant psychological or
psychiatric problems associated with IIH, particularly if the condition itself is of long
duration, but also if, as considered above, there is prolonged elevation of CSF pressure
despite amelioration of symptoms and signs.
96
There are several reports of a coincidence of IIH and depression. The only
formal examination of a possible association is the study by Kleinschmidt et
al. who compared three groups of patients: 1) IIH patients, 2) age and
weight-matched controls, 3) age-matched controls of normal weight. They
found higher levels of depression and anxiety, and a greater number of
adverse health problems in the IIH group compared to both control groups
whereas there were no differences with respect to non-health-related
psychosocial problems.154
♦Persistent elevation of CSF pressure
It was evident from the findings using continuous ICP monitoring as part
of the follow-up after clinically successful treatment of IIH with steroids
that despite the undoubted resolution of all clinical symptoms and signs,
there could be a persistent and not insubstantial increase in CSF pressure.
Using single manometric readings of CSF pressure on lumbar puncture, a
similar claim could be made for apparently successful treatment by subtemporal decompression. More recently, similar findings were obtained in a
small group of patients treated by optic nerve sheath decompression and
direct treatment of cranial venous outflow obstruction.153
11. Recurrence
Clearly, reported recurrence rates will depend substantially on three major
factors: duration of follow-up, the type of initial treatment, and the duration
of the initial treatment. Many of the reported recurrences occurred well
within the first 12 months from diagnosis and in part, at least, might be
attributable to premature cessation of treatment. Likewise, shunt
malfunction in shunted patients may be considered a recurrence, although
this is different in nature from recurrence as usually understood.153
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