Download Medial surface Central sulcus on axial imaging cs cs pM pocs

eye movements to the opposite direction
Medial surface
LG
(Figure 5-2)
CT
The cingulate sulprcs CENTRAL SULCUS
cus terminates posteriPL
pM
orly in the pars
SFG
marginalis (pM) (plusps
cins
ins
c
ral: partes marginales).
PCu
Cin
G
On axial imaging, the
MRI
pMs: are visible on 95%
callosum
p us
pos
of CTs and 91% of
cor
MRIs4, are usually the
most prominent of the
Cu
paired grooves straddling the midline, and
they extend a greater
pons
distance into the
hemispheres4. On axial
CT, the pM is located
slightly posterior to the
widest biparietal
diameter4; on the typiFigure 5-2 Medial aspect of the right hemisphere
cally more horizontally
“CT” & “MRI” bars depict typical axial slice orientation for CT & MRI scans.
oriented MRI slices the
See Table 5-1 and Table 5-2 for abbreviations
pM assumes a more
posterior position. The
pMs curve posteriorly in lower slices and anteriorly in higher slices (here, the paired pMs
form the “pars bracket” - a characteristic “handlebar” configuration straddling the midline).
Pointers:
• parieto-occipital sulcus (pos) (or
fissure): more prominent over the
medial surface, and on axial imaging is longer, more complex, and
more posterior than the pars
marginalis5
• post-central sulcus (pocs): usually
bifurcates and forms an arc or parenthesis (“lazy-Y”) cupping the
pM. The anterior limb does not enter the pM-bracket and the posterior limb curves behind the pM to
enter the IHF
NEUROSURGERY
cs
CG
cs
Pre
PL
See Figure 5-3. Identification is
important to localize the motor strip
(contained in the PreCG). The central
sulcus (CS) is visible on 93% of CTs
and 100% of MRIs4. It curves posteriorly as it approaches the interhemispheric fissure (IHF), and often terminates
in the paracentral lobule, just anterior
to the pars marginalis (pM) within the
pars bracket (see above)4 (i.e. the CS often does not reach the midline).
SFG
Central sulcus on axial imaging
tCG
Pos
pocs
pM
Figure 5-3 CT scan (upper cut) showing gyri/sulci.
See Table 5-1 and Table 5-2 for abbreviations
5.1. Surface anatomy
85
Table 5-2 Cerebral gyri and lobules
(abbreviations)
Table 5-1 Cerebral sulci
(abbreviations)
cins
cs
ips-ios
los
pM
pocn
pocs
pof
pos
prcs
sfs, ifs
sps
sts, its
tos
5.1.2.
cingulate sulcus
central sulcus
intraparietal-intraoccipital sulcus
lateral occipital sulcus
pars marginalis
pre-occipital notch
post-central sulcus
parieto-occipital fissure
parieto-occipital sulcus
pre-central sulcus
superior, inferior frontal
sulcus
superior parietal sulcus
superior, inferior temporal sulcus
trans occipital sulcus
AG
CinG
Cu
LG
MFG, SFG
OG
PCu
PreCG, PostCG
PL
IFG
POp
PT
POr
angular gyrus
cingulate gyrus
cuneus
lingual gyrus
middle & superior frontal gyrus
orbital gyrus
precuneous
pre- and post-central gyrus
paracentral lobule (upper SFG and PreCG
and PostCG)
inferior frontal gyrus
pars opercularis
pars triangularis
pars orbitalis
STG, MTG, ITG superior, middle & inferior temporal gyrus
SPL, IPL
superior & inferior parietal lobule
SMG
supramarginal gyrus
Surface anatomy of the cranium
CRANIOMETRIC POINTS
IP
IT
AL
O
C
C
GWS
cs
See Figure 5-4.
Pterion: region
vertex
where the following
bregma
bones are approximatPARIE
ed: frontal, parietal,
TAL
AL
stephanion
temporal and sphenoid
NT
O
R
(greater wing). EstiF
pterion
mated as 2 fingerstl
lambda
breadths above the zyophyron
sqs
gomatic arch, and a
glabella
thumb’s breadth benasion
hind the frontal proTEMPORAL
rhinion
ls
cess of the zygomatic
pms
sms
bone (blue circle in FigID
ure 5-4).
TO s
G
Asterion: juncNASAL
ZY
AS om
M
tion of lambdoid, occipinion
prosthion
itomastoid and
MAXILLA
parietomastoid suasterion
inferior
tures. Usually lies
opisthion
alveolar point
within a few millimeE
gonion
IBL
gnathion
ters of the posterior-inD
N
MA
or menton
ferior edge of the
junction of the transverse and sigmoid siFigure 5-4 Craniometric points & cranial sutures.
nuses (not always
Named bones appear in all upper case letters.
reliable6 - may overlie
Abbreviations: GWS = greater wing of sphenoid bone, NAS = nasal bone, stl =
either sinus).
superior temporal line, ZYG = zygomatic.
Vertex: the topSutures: cs = coronal, ls = lambdoid, oms = occipitomastoid, pms = parietomasmost point of the skull. toid, sms = squamomastoid, sqs = squamosal
Lambda: junction of the lambdoid
and sagittal sutures.
Stephanion: junction of coronal suture and superior temporal line.
86
5. Neuroanatomy and physiology
NEUROSURGERY
Glabella: the most forward projecting point of the forehead at the level of the supraorbital ridge in the midline.
Opisthion: the posterior margin of the foramen magnum in the midline.
Bregma: the junction of the coronal and sagittal sutures.
Sagittal suture: midline suture from coronal suture to lambdoid suture. Although
often assumed to overlie the superior sagittal sinus (SSS), the SSS lies to the right of the
sagittal suture in the majority of specimens7 (but never by > 11 mm).
The most anterior mastoid point lies just in front of the sigmoid sinus8.
RELATION OF SKULL MARKINGS TO CEREBRAL ANATOMY
Taylor-Haughton lines
ce n
tral
sulc
us
Taylor-Haughton (T-H)
2 cm
1/2
lines can be constructed on an
angiogram, CT scout film, or
skull x-ray, and can then be reconstructed on the patient in the
O.R. based on visible external
3/4
landmarks9. T-H lines are
shown as dashed lines in Figure
5-5.
1. Frankfurt plane, AKA
re
baseline: line from inferissu
n fi
or margin of orbit
vi a
l
y
s
through the upper margin of the external auditory meatus (EAM) (as
distinguished from ReEAM
id’s base line: from infeFrankfurt
rior orbital margin
plane
through the center of the
EAM)10 (p 313)
posterior ear line
2. the distance from the nacondylar line
sion to the inion is measured across the top of
the calvaria and is divided into quarters (can be
Figure 5-5 Taylor-Haughton lines
done simply with a piece
and other localizing methods
of tape which is then
folded in half twice)
3. posterior ear line: perpendicular to the baseline through the mastoid process
4. condylar line: perpendicular to the baseline through the mandibular condyle
5. T-H lines can then be used to approximate the sylvian fissure (see below) and the
motor cortex (also see below)
©2001 Mark S Greenberg, M.D.
All rights reserved.
Unauthorized use is prohibited.
Sylvian fissure AKA lateral fissure
Approximated by a line connecting the lateral canthus to the point 3/4 of the way
posterior along the arc running over convexity from nasion to inion (T-H lines).
Angular gyrus
Located just above the pinna, important on the dominant hemisphere as part of
Wernicke’s area. Note: there is significant individual variability in the location2.
Angular artery
Located 6 cm above the EAM.
Motor cortex
Numerous methods utilize external landmarks to locate the motor strip (pre-central
gyrus) or the central sulcus (Rolandic fissure) which separates motor strip anteriorly
from primary sensory cortex posteriorly. These are just approximations since individual
variability causes the motor strip to lie anywhere from 4 to 5.4 cm behind the coronal
suture11. The central sulcus cannot even be reliably identified visually at surgery12.
• method 1: the superior aspect of the motor cortex is almost straight up from the
EAM near the midline
• method 213: the central sulcus is approximated by connecting:
NEUROSURGERY
5.1. Surface anatomy
87
cs
•
A. the point 2 cm posterior to the midposition of the arc extending from nasion
to inion (illustrated in Figure 5-5), to
B. the point 5 cm straight up from the EAM
method 3: using T-H lines, the central sulcus is approximated by connecting:
A. the point where the “posterior ear line” intersects the circumference of the
skull (see Figure 5-5) (usually about 1 cm behind the vertex, and 3-4 cm behind the coronal suture), to
B. the point where the
“condylar line” intersects the line
representing the
sylvian fissure
method 4: a line drawn
B
45° to Reid’s base line
starting at the pterion
D1
FM
F
A O
points in the direction of
V3
the motor strip14 (p 584-5)
Aq
T
Twining
•
D2
V4
RELATIONSHIP OF VENTRICLES
D3
D4
TO SKULL
Figure 5-6 shows the relationship of non-hydrocephalic
opisthion
ventricles to the skull in the latbaseline
eral view. Some dimensions of interest are shown in Table 5-315.
sigmoid sinus
In the non-hydrocephalic
sella turcica
adult, the lateral ventricles lie 45 cm below the outer skull surface. The center of the body of the
Figure 5-6 Relationship of ventricles to skull landmarks*
lateral ventricle sits in the midp* Abbreviations: (F = frontal horn, B = body, A = atrium, O = ocupillary line, and the frontal
cipital horn, T = temporal horn) of lateral ventricle. FM = forahorn is intersected by a line passmen of Monro. Aq = sylvian aqueduct. V3 = third ventricle. V4
ing perpendicular to the calvaria
= fourth ventricle. cs = coronal suture. Dimensions D1-4 →
along this line16. The anterior
see Table 5-3
horns extend 1-2 cm anterior to
the coronal suture.
Average length of third ventricle ≈ 2.8 cm.
Table 5-3 Dimensions from Figure 5-6
Dimension
(see Figure 5-6)
D1
D2
D3
D4
*
88
Description
Lower limit
(mm)
length of frontal horn anterior to FM
distance from clivus to floor of 4th ventricle at
level of fastigium*
length of 4th ventricle at level of fastigium*
distance from fastigium* to opisthion
Upper limit
(mm)
33.3
Average
(mm)
25
36.1
10.0
30.0
14.6
32.6
19.0
40.0
40.0
the fastigium is the apex of the 4th ventricle within the cerebellum
5. Neuroanatomy and physiology
NEUROSURGERY
5.1.3.
Surface landmarks of spine levels
Estimates of cervical levels for anterior cervical
spine surgery may be made using the landmarks shown
in Table 5-4. Intra-operative C-spine x-rays are essential
to verify these estimates.
The scapular spine is located at about T2-3.
The inferior scapular pole is ≈ T6 posteriorly.
Intercristal line: a line drawn between the highest point of the iliac crests across the back will cross the
midline either at the interspace between the L4 and L5
spinous processes, or at the L4 spinous process itself.
5.2.
Table 5-4 Cervical levels17
Level
Landmark
C1-2 angle of mandible
C3-4 1 cm above thyroid cartilage (≈ hyoid bone)
C4-5 level of thyroid cartilage
C5-6 crico-thyroid membrane
C6
carotid tubercle
C6-7 cricoid cartilage
Cranial foramina & their contents
Table 5-5 Cranial foramina and their contents*
Foramen
nasal slits
superior orbital fissure
Contents
anterior ethmoidal nn., a. & v
Cr. Nn. III, IV, VI, all 3 branches of V1 (ophthalmic division divides into nasociliary, frontal, and lacrimal nerves); superior ophthalmic vv.; recurrent meningeal br. from lacrimal
a.; orbital branch of middle meningeal a.; sympathetic filaments from ICA plexus
inferior orbital fissure
Cr. N. V-2 (maxillary div.), zygomatic n.; filaments from pterygopalatine branch of maxillary n.; infraorbital a. & v.; v. between inferior ophthalmic v. & pterygoid venous plexus
foramen lacerum
usually nothing (ICA traverses the upper portion but doesn’t enter, 30% have vidian a.)
carotid canal
internal carotid a., ascending sympathetic nerves
incisive foramen
descending septal a.; nasopalatine nn.
greater palatine foramen greater palatine n., a., & v.
lesser palatine foramen lesser palatine nn.
internal acoustic meatus Cr. N. VII (facial); Cr. N. VIII (stato-acoustic) - (see text & Figure 5-7 below)
hypoglossal canal
Cr. N. XII (hypoglossal); a meningeal branch of the ascending pharyngeal a.
foramen magnum
spinal cord (medulla oblongata); Cr. N. XI (spinal accessory nn.) entering the skull; vertebral aa.; anterior & posterior spinal arteries
foramen cecum
occasional small vein
cribriform plate
olfactory nn.
optic canal
Cr. N. II (optic); ophthalmic a.
foramen rotundum
Cr. N. V2 (maxillary div.), a. of foramen rotundum
foramen ovale
Cr. N. V3 (mandibular div.) + portio minor (motor for CrN V)
foramen spinosum
middle meningeal a. & v.
jugular foramen
internal jugular v. (beginning); Cr. Nn. IX, X, XI
stylomastoid foramen Cr. N. VII (facial); stylomastoid a.
condyloid foramen
v. from transverse sinus
mastoid foramen
v. to mastoid sinus; branch of occipital a. to dura mater
*
Abbreviations: a. = artery, aa. = arteries, v. = vein, vv. = veins, n. = nerve, nn. = nerves, br. = branch, Cr.
N. = cranial nerve, fmn. = foramen, div. = division
Porus acusticus
AKA internal auditory canal (see Figure 5-7)
The filaments of the acoustic portion of VIII penetrate tiny openings of the lamina
cribrosa of the cochlear area18.
Transverse crest: separates superior vestibular area and facial canal (above) from
the inferior vestibular area and cochlear area (below)18.
Vertical crest (AKA Bill’s bar): separates the meatus to facial canal anteriorly (conNEUROSURGERY
5.2. Cranial foramina & their contents
89
taining VII and nervus intermedius) from the vestibular area posteriorly (containing the
superior division of vestibular nerve).
The “5 nerves” of the IAC:
1. facial nerve (VII)
(mnemonic: “7-up”
facial canal (Cr. N. VII with NI*)
as VII is in superior portion)
vertical crest (”Bill’s bar”)
2. nervus intermedisuperior vestibular area (superior
us: the somatic
vestibular nerve) (to utricle &
sensory branch of
superior & lateral semicircular canals)
the facial nerve
primarily innertransverse crest (crista falciformis)
vating mechanoreinferior
vestibular area
ceptors of the hair
(inferior
(to saccule)
follicles on the investibular
foramen singulare (to
ner surface of the
posterior semicircular canal) nerve)
pinna and deep
mechanoreceptors
tractus spiralis foraminosus (cochlear
of nasal and buccal
area) (acoustic portion of Cr. N. VIII)
cavities and
chemoreceptors in
the taste buds on Figure 5-7 Right internal auditory canal (porus acusticus) & nerves
the anterior 2/3 of * NI = nervus intermedius
the tongue
3. acoustic portion of the VIII nerve (mnemonic: “Coke down” for cochlear portion)
4. superior branch of vestibular nerve: passes through the superior vestibular area
to terminate in the utricle and in the ampullæ of the superior and lateral semicircular canals
5. inferior branch of vestibular nerve: passes through inferior vestibular area to terminate in the saccule
5.3.
Cerebellopontine angle anatomy
retractor
on cerebellar
hemisphere
foramen of
Luschka
foramen of
Magendie
cerebellar
tonsil
PICA
V
Meckel's
cave
pons
flocculus
choroid
plexus
VII
IAC
VIII
IX
jugular
foramen
X
XI
XII
olive
medulla
Figure 5-8 Normal anatomy of right cerebellopontine angle viewed
from behind (as in a suboccipital approach)18
90
5. Neuroanatomy and physiology
NEUROSURGERY
5.4.
Occiptoatlantoaxial-complex anatomy
≈ 50% of head rotation occurs at the C1-2 (atlantoaxial) joint.
Ligaments of the occipito-atlanto-axial complex
apical
odontoid
ligament
cruciate ligament,
ascending band
anterior
atlantooccipital
membrane
anterior transverse
ligament
longitudinal
ligament
cruciate ligament,
descending band
tectorial
membrane
posterior
longitudinal
ligament
posterior
atlantooccipital
membrane
C1
ligamentum
flavum
spinal
cord
C2
C3
Figure 5-9 Sagittal view of the ligaments of the craniovertebral junction
Modified with permission from “In Vitro Cervical Spine Biomechanical Testing” BNI Quarterly,
Vol.9, No. 4, 1993
Stability of this joint complex is primarily due to ligaments, with little contribution
from bony articulations and joint capsules (see Figure 5-9 through Figure 5-11):
1. ligaments that connect the atlas to the occiput:
A. anterior atlanto-occipiascending
tal memclivus
band
brane: cephalright alar
ad extension
ligament
of the anterior longitudinal ligament.
accessory
Extends from
(deep) portion
anterior marof tectorial
C1
gin of foramembrane
men magnum
transverse
(FM) to anteCRUCIATE
band
rior arch of C1
LIGAMENT
B. posterior atdescending
lanto-occipiC2
band
tal membrane: connects the posFigure 5-10 Dorsal view of the cruciate and alar ligaments
terior margin
Viewed with tectorial membrane removed.
of the FM to
Modified with permission from “In Vitro Cervical Spine Biomechanical
posterior arch
Testing” BNI Quarterly, Vol.9, No. 4, 1993
of C1
C. the ascending band of the cruciate ligament
2. ligaments that connect the axis (viz. the odontoid) to the occiput:
A. tectorial membrane: some authors distinguish 2 components
1. superficial component: cephalad continuation of the posterior longituNEUROSURGERY
5.4. Occiptoatlantoaxial-complex anatomy
91
3.
dinal ligament. A strong band connecting the dorsal surface of the
dens to the ventral surface of the FM above, and dorsal surface of C2
& C3 bodies below
2. accessory (deep) portion: located laterally, connects C2 to occipital
condyles
B. alar (“check”) ligaments19
1. occipito-alar portion: connects side of the dens to occipital condyle
2. atlanto-alar portion: connects side of the dens to the lateral mass of C1
C. apical odontoid ligament: connects tip of
odontoid
right alar
dens to the FM. Little
process
ligament
mechanical strength
transverse
ligaments that connect the
ligament
axis to the atlas:
A. transverse (atlantoaxial) ligament: the
horizontal component
of the cruciate ligatubercle
tectorial
ment. Traps the dens
membrane
against the anterior atlas via a strap-like
mechanism (see Figure
posterior arch C1
5-11). Provides the majority of the strength
Figure 5-11 C1 viewed from above, showing the trans(“the strongest ligaverse and alar ligaments
ment of the spine”20)
Modified with permission from “In Vitro Cervical Spine BioB. atlanto-alar portion of
mechanical Testing” BNI Quarterly, Vol.9, No. 4, 1993
the alar ligaments (see
above)
C. descending band of the cruciate ligament
The most important structures in maintaining atlanto-occipital stability are the tectorial membrane and the alar ligaments. Without these, the remaining cruciate ligament and apical dentate ligament are insufficient.
5.5.
Spinal cord anatomy
5.5.1.
Spinal cord tracts
Figure 5-12 depicts a cross-section of a typical spinal cord segment, combining some
elements from different levels (e.g. the intermediolateral grey nucleus is only present
from T1 to ≈ L1 or L2 where there are sympathetic (thoracolumbar outflow) nuclei). It is
schematically divided into ascending and descending halves, however, in actuality, ascending and descending paths coexist on both sides.
Table 5-6 Descending (motor) tracts (↓) in Figure 5-12
Number (see
Figure 5-12)
1
2
3
4
5
6
92
Path
anterior corticospinal tract
medial longitudinal fasciculus
vestibulospinal tract
medullary (ventrolateral) reticulospinal tract
rubrospinal tract
lateral corticospinal (pyramidal) tract
Function
Side of body
skilled movement
?
facilitates extensor muscle tone
automatic respirations?
flexor muscle tone
skilled movement
5. Neuroanatomy and physiology
opposite
same
same
same
same
same
NEUROSURGERY
Table 5-7 Bi-directional tracts in Figure 5-12
Number (see
Path
Figure 5-12)
7
dorsolateral fasciculus (of Lissauer)
8
fasciculus proprius
Function
short spinospinal connections
Table 5-8 Ascending (sensory) tracts (↑) in Figure 5-12
Number (see
Figure 5-12)
9
10
11
12
13
14
15
Path
Function
Side of
body
joint position, fine touch, same
vibration
fasciculus gracilis
fasciculus cuneatus
posterior spinocerebellar tract
lateral spinothalamic tract
anterior spinocerebellar tract
spinotectal tract
anterior spinothalamic tract
stretch receptors
pain & temperature
whole limb position
unknown, ? nociceptive
light touch
same
opposite
opposite
opposite
opposite
Figure 5-12 also depicts some of the laminae according to the scheme of Rexed. Lamina II is equivalent to the substantia gelatinosa. Laminae III and IV are the nucleus proprius. Lamina VI is located in the base of the posterior horn.
bi-directional
paths
7
8
S TC
6
SENSORY
(ascending
paths)
{
{
{
MOTOR
(descending
paths)
S = sacral
T = thoracic
C = cervical
I
II
III
intermediolateral
grey nucleus
(sympathetic)
9
10
IV
5
11
12
V
STC
VI
X
VII
VIII
IX
IX
CTS dentate
ligament
4
3
13
14
2
2.5-4
1
15
cm
anterior spinal
artery
anterior motor
nerve root
Figure 5-12 Schematic cross-section of cervical spinal cord
SENSATION
PAIN & TEMPERATURE: BODY
Receptors: free nerve endings (probable).
1st order neuron: small, finely myelinated afferents; soma in dorsal root ganglion
(no synapse). Enter cord at dorsolateral tract (zone of Lissauer). Synapse: substantia geNEUROSURGERY
5.5. Spinal cord anatomy
93
latinosa (Rexed II).
2nd order neuron axon cross obliquely in the anterior white commissure ascending
≈ 1-3 segments while crossing to enter the lateral spinothalamic tract.
Synapse: VPL thalamus. 3rd order neurons pass through IC to postcentral gyrus
(Brodmann’s areas 3, 1, 2).
FINE TOUCH, DEEP PRESSURE & PROPRIOCEPTION: BODY
Fine touch AKA discriminative touch. Receptors: Meissner’s & pacinian corpuscles,
Merkel’s disks, free nerve endings.
1st order neuron: heavily myelinated afferents; soma in dorsal root ganglion (no
synapse). Short branches synapse in nucleus proprius (Rexed III & IV) of posterior gray;
long fibers enter the ipsilateral posterior columns without synapsing (below T6: fasciculus gracilis; above T6: fasciculus cuneatus).
Synapse: nucleus gracilis/cuneatus (respectively), just above pyramidal decussation. 2nd order neuron axons form internal arcuate fibers, decussate in lower medulla as
medial lemniscus.
Synapse: VPL thalamus. 3rd order neurons pass through IC primarily to postcentral gyrus.
ANTERIOR
trigeminal
nerve
{
POSTERIOR
V1
V2
V3
C2
superior clavicular
occipitals
C2
C3
INTERCOSTALS
posterior
lateral
medial
axillary
RADIAL
post. cutaneous
dorsal cutan.
C3
C4
T3
T4
T2
T6
T8
T1
C6
T1
T1
T4
L1
C5
T6
T8
T2
T10
0
T12
musculocutan.
medial cutan.
2
©2001 Mark S Greenberg, M.D.
All rights reserved.
Unauthorized use is prohibited.
S4
C5
C4
T2
radial
T1
C6
clunials
S5
S3
C8
L2
C7
ilioinguinal
lateral cutan.
nerve of thigh
L3
L4
C8
median
L3
ulnar
FEMORAL posterior
cutaneous
anterior
cutaneous
saphenous
L5
SCIATIC
COMMON PERONEAL
lat. cutan.
sup. peroneal
deep peroneal
S1
TIBIAL
sural
plantars
D E R M AT O M E S
(anterior)
{
L4
S1
C7
L5
L4
S1
med.
lat.
C U TA N E O U S
NERVES
D E R M AT O M E S
(posterior)
Figure 5-13 Dermatomal and sensory nerve distribution
(Redrawn from “Introduction to Basic Neurology”, by Harry D. Patton, John W. Sundsten, Wayne E. Crill and
Phillip D. Swanson, © 1976, pp 173, W. B. Saunders Co., Philadelphia, PA, with permission)
LIGHT (CRUDE) TOUCH: BODY
Receptors: as fine touch (see above), also peritrichial arborizations.
94
5. Neuroanatomy and physiology
NEUROSURGERY
1st order neuron: large, heavily myelinated afferents (Type II); soma in dorsal root
ganglion (no synapse). Some ascend uncrossed in post. columns (with fine touch); most
synapse in Rexed VI & VII.
2nd order neuron axons cross in anterior white commissure (a few don’t cross); enter
anterior spinothalamic tract.
Synapse: VPL thalamus. 3rd order neurons pass through IC primarily to postcentral gyrus.
5.5.2.
Dermatomes and sensory nerves
Figure 5-13 shows anterior and posterior view, each schematically separated into
sensory dermatomes (segmental) and peripheral sensory nerve distribution.
5.5.3.
Spinal cord vasculature
basilar artery
spinal cord
radicular artery at C3
anterior spinal artery
radicular artery at C6
right vertebral
artery
right common
carotid
deep cervical artery
left vertebral
artery
costocervical trunk
left common
carotid
right
subclavian
brachiocephalic trunk
radicular artery at C8
left subclavian
left posterior spinal artery
radicular artery at T5
aorta
posterior intercostal artery
(dorsal branch)
posterior
spinal arteries
radicular
artery
aorta
Axial view
posterior
intercostal
artery
anterior
spinal
artery
}
intercostal arteries
artery of
Adamkiewicz
(arteria radicularis
anterior magna)
arteria radicularis
magna
(posterior branch)
Figure 5-14 Schematic diagram of spinal cord arterial supply
Modified from Diagnostic Neuroradiology, 2nd ed., Volume II, pp. 1181, Taveras J M, Woods EH, editors, ©
1976, the Williams and Wilkins Co., Baltimore, with permission)
Although a radicular artery from the aorta accompanies the nerve root at many levels, most of these contribute little flow to the spinal cord itself. The anterior spinal artery
is formed from the junction of two branches, each from one of the vertebral arteries. Major contributors of blood supply to the anterior spinal cord is from 6-8 radicular arteries
NEUROSURGERY
5.5. Spinal cord anatomy
95
at the following levels (“radiculomedullary arteries”, the levels listed are fairly consistent, but the side varies21 (p 1180-1)):
• C3 - arises from vertebral artery
≈ 10% of population lack an an• C6 - usually arises from deep cervical artery
terior radicular artery in lower
• C8 - usually from costocervical trunk
cervical spine22
• T4 or T5
• artery of Adamkiewicz AKA arteria radicularis anterior magna
A. the main arterial supply for the spinal cord from ≈ T8 to the conus
B. located on the left in 80%23
C. situated between T9 & L2 in 85% (between T9 & T12 in 75%); in remaining
15% between T5 & T8 (in these latter cases, there may be a supplemental
radicular artery further down)
D. usually fairly large, gives off cephalic and caudal branch (latter is usually
larger) giving a characteristic hair-pin appearance on angiography
}
The paired posterior spinal arteries are less well defined than the anterior spinal
artery, and are fed by 10-23 radicular branches.
The midthoracic region has a tenuous vascular supply (“watershed zone”), possessing only the above noted artery at T4 or T5. It is thus more susceptible to vascular insults.
ANATOMIC VARIANTS
Arcade of Lazorthes: normal variant where the anterior spinal artery joins with
the paired posterior spinal arteries at the conus medullaris.
5.6.
Cerebrovascular anatomy
5.6.1.
Cerebral vascular territories
AXIAL VIEW
CORONAL VIEW
anterior cerebral
artery
middle cerebral
artery
RAH
MCA
AChA
internal carotid
PCommA
basilar artery
anterior choroidal
artery
posterior cerebral
artery
RAH = recurrent artery of Heubner
Figure 5-15 Vascular territories of the cerebral hemispheres
Figure 5-15 depicts approximate vascular distributions of the major cerebral arteries. There is considerable variability of the major arteries24 as well as the central distri96
5. Neuroanatomy and physiology
NEUROSURGERY