Download Document

Pamela BL
 The
scalp is the anatomical area that extends
from the supraorbital margins of the frontal
bones to the superior nuchal lines of the
occipital bones and laterally extends over
the temporal fascia to the zygomatic arches.
 The
1.
2.
3.
4.
5.
scalp consists of five layers of tissue:
Skin
Connective tissue
Aponeurosis
Loose connective tissue
Pericranium
 Skin,
thin except in the occipital region.
 Contains many sweat and sebaceous glands,
and hair follicles.
 Has an abundant arterial supply.
 Has good venous and lymphatic drainage.
 Connective
tissue, forms the thick, dense,
richly vascular zed subcutaneous layer that is
well supplied with cutaneous nerves.
 Aponeurosis,
the epicranial aponeurosis-a
strong tendinous sheet that covers the
calvaria btwn the occipitalis, superior
auricular and frontalis muscles(these
structures constitute the epicranius muscle).
 The
frontalis; pulls the scalp anteriorly,
wrinkles the forehead and elevates the
eyebrows.
 The occipitalis; pulls the scalp posteriorly
and wrinkles the skin at the back of the
neck.
 Loose
connective tissue, spongy like because
of its many potential spaces that may distend
with fluid resulting from injury/infection.
 This layer allows free movement of the 1st
three layers over the underlying calvaria.
 Pericranium,
a dense layer of connective
tissue that forms the external periosteum of
the calvaria.
 It is firmly attached but can be stripped
fairly easily from the calvaria of living people
except where it is continuous with the
fibrous tissue in the cranial sutures.
 Innervation
of the scalp anterior to the
auricles is through branches of all three
divisions of cranial nerve V, the trigeminal
nerve.
 Posterior to the auricles, the nerve supply is
from spinal cutaneous nerves(C2 and C3).
 The
blood vessels run in layer two of the
scalp-the dense subcutaneous layer btwn the
skin and epicranial aponeurosis.
 They are held by the dense connective tissue
in such a way that they tend to remain open
when cut.
 Consequently, bleeding from the scalp wound
is profuse.
 Arterial
supply of the scalp is from the
external carotid artery through the occipital,
posterior auricular and superficial temporal
arteries.
 The scalp also receives blood supply from the
internal carotid artery through the
supraorbital and supratrochlear arteries.
 The
scalp has a rich blood supply, and the
arteries anastomose freely with one another
in the dense subcutaneous connective tissue
layer
 The
venous drainage of superficial parts of
the scalp is through the accompanying veins
of the scalp arteries-the supraorbital and
supratrochlear veins, which begin in the
forehead and descend to unite at the medial
angle of the eye to form the angular vein
that becomes the facial vein at the inferior
margin of the orbit.
 The
superficial temporal veins and posterior
auricular veins drain the scalp anterior and
posterior to the auricles respectively.
 The occipital veins drain the occipital region
of the scalp.
 Venous drainage of deep parts of the scalp in
the temporal region is through deep
temporal veins(tributaries of pterygoid
venous plexus).
 There
are no lymph nodes in the scalp.
 Lymph from this region drains into the
superficial ring(pericervical collar) of lymph
nodes- submental, submandibular, parotid,
mastoid/retroauricular and occipital, that is
located at the junction of the head and
neck.
 Lymph from these nodes drains into the deep
cervical lymph nodes along the IJV.
 Scalp
infections-the loose connective tissue
of the scalp is the dangerous area of the
scalp because pus or blood can easily spread
in it.
 Infection in this layer can also pass into the
cranial cavity through the emissary veins that
pass through parietal foramina in the calvaria
and infect intracranial structures such as the
brain and meninges.
 An
infection cannot pass into the neck
because the occipitalis muscle attaches to
the occipital bone and mastoid parts of the
temporal bones.
 Neither can a scalp infection spread laterally
beyond the zygomatic arches because the
epicranial aponeurosis is continuous with the
temporal fascia that attaches to these
arches.
 An
infection or fluid(blood/pus) can enter
the eyelids and the root of the nose because
the frontalis inserts into the skin and
subcutaneous and does not attach to the
bone.
 Consequently, black eyes result from injury
to the scalp/forehead.
 Most blood enter the upper eyelid, but some
may also enter the lower one.
 Scalp
lacerations-are the most common type
of head injury requiring surgical care.
 These wounds bleed profusely because the
arteries entering the periphery of the scalp
bleed from both ends due to abundant
anastomoses.
 They do not retract when lacerated because
they are held open by the dense connective
tissue in the 2nd layer of the scalp.
 Hence
an unconscious patient may bleed to
death from scalp lacerations if bleeding not
controlled.
 The epicranial aponeurosis is clinically
important.
 Because of its strength, laceration in the skin
does mot gape because the margins of the
wound are held together by this aponeurosis.
 Furthermore,
when suturing superficial scalp
wounds, deep sutures are not necessary
because the epicranial aponeurosis does not
allow wide separation of the skin.
 Deep scalp wounds gape widely when the
epicranial aponeurosis is spilt or lacerated in
the coronal plane because of the pull of the
frontal and occipital bellies of epicranius
muscle in opposite directions.
 Cephalotoma,
sometimes during a difficult
birth, bleeding occurs btwn the baby’s
pericranium and calvaria usually over one
parietal bone.
 The bleeding results from rupture of
multiple, minute periosteal arteries that
nourish the bones of the calvaria.
 The resulting collection of blood developing
several hours after birth is a
cephalohematoma.
 The
cranial meninges are internal to the
skull.
 The cranial meninges:
1. Protect the brain
2. Form the supporting framework foe
arteries, veins and venous sinuses
 Enclose a fluid filled cavity, the
subarachnoid space(leptomeningeal) which
is vital to the normal function of the brain.
 The
1.
2.
3.
cranial meninges consist of three layers:
Dura mate(dura)an external, thick fibrous
membrane
Arachnoid mater(arachnoid-an
intermediate, delicate membrane
Pia mater(pia)-an internal, delicate
vascular membrane.)
 The
meninges also enclose the cerebrospinal
fluid and help to maintain the balance of
extracellular fluid in the brain.
 CSF is a clear liquid similar to blood in
constitution but has less proteins and a
different ion concentration.
 CSF
is formed by the choroid plexuses of the
four ventricles of the brain, leaves the
ventricular system and enters the
subarachnoid space btwn the arachnoid and
pia mater where it cushions and nourishes
the brain.
 The
dura mater(pachymeninx-thick
membrane) a two layered membrane, is
adherent to the internal surface of the skull.
 It consists of:
1. An external periosteal layer, formed by the
periosteum covering the internal surface of
the calvaria
2. An internal meningeal layer, a strong
fibrous membrane that is continuous at the
foramen magnum with the spinal dura
mater covering the spinal cord.
 The
external periosteal layer is continuous at
the cranial foramina with the periosteum on
the external surface of the calvaria.
 It is not continuous with the dura mater of
the spinal cord.
 The meningeal layer is intimately fused with
the periosteal layer and cannot be separated
from it.
 In
the cranial base the two dural layers are
firmly attached and difficult to separate
from the bones.
 The
internal meningeal layer of dura draws
away from the external periosteal layer of
dura to form dural infoldings(reflections),
which separate the regions of the brain from
each other.
 The largest of these septa is falx
cerebri(cerebral falx).
 These dural infoldings divide the cranial
cavity into compartments that support parts
of brain.
 The
dural infoldings include:
 Falx cerebri(cerebral falx)
 Tentorium cerebelli(cerebellar tentorium)
 Diaphragma sellae(sellar diaphragm)
 Falx is the Latin for sickle, the falces are
sickle shaped structures.
 The
falx cerebri, the largest dural reflection
lies in the longitudinal fissure and separates
the right and left cerebral hemispheres.
 The falx cerebri attaches in the median
plane of the internal surface of the calvaria,
from the frontal crest of the frontal bone
and crista galli of the ethmoid bone
anteriorly to the internal occipital
protuberance posteriorly.
 The
falx cerebri ends by becoming
continuous with the tentorium cerebelli.
 The tentorium cerebelli, the 2nd largest dural
infolding, is a wide crescentic septum that
separates the occipital lobes of the cerebral
hemispheres from the cerebellum.
 The tentorium cerebelli attaches rostrally to
the clinoid processes of the sphenoid bone,
rostrilaterally to the petrous part of
temporal bone and posterolaterally to the
internal surface of the occipital bone.
 The
falx cerebri attaches to the tentorium
cerebelli and hold it up, giving it a tent like
appearance.
 The tent like shape of the cerebelli
tentorium divides the cranial cavity into
supratentorial and infratentorial
compartments.
 The
supratentorial compartment is divided
into right and left halves by the falx cerebri.
 Its concave anteromedial border is free,
producing a gap-the tentorial notch/incisura
of tentorium through which the brainstem
extends from the posterior into the middle
cranial fossa.
 The
cerebellar falx is a vertical dural
infolding that lies inferior to the tentorium
cerebelli in the posterior part of the
posterior cranial fossa, it partially separates
the cerebellar hemispheres.
 The
diaphragma sellae, the smallest dural
infolding, is a circular sheet of dura that is
suspended btwn the clinoid processes
forming a roof over the hypophysial fossa in
the sphenoid bone.
 The diaphragma sellae covers the pituitary
gland in this fossa and has an aperture for
passage of the infundibulum(pituitary stalk)
and hypophyseal veins.
 Tentorial
herniation-the opening in the
tentorium cerebelli for the brainstem is
slightly larger than necessary to
accommodate the midbrain.
 Space occupying lesions like tumors in the
supratentorial compartment produce
increased intracranial pressure and may
cause part of the adjacent temporal lobe of
the brain to herniate through the tentorial
notch.
 During
tentorial herniation, the temporal
lobe may be lacerated by the tough
tentorium cerebelli and the oculomotor
nerve may be stretched/compressed or both.
 Such oculomotor lesions produce paralysis of
the extrinsic eye muscles supplied by
oculomotor nerve.
 The
dural venous sinuses are endothelium
lined spaces btwn the periosteal and
meningeal layers of the dura, they form
where the dural septa attach.
 Large veins from the surface of the brain
empty into these sinuses.
 And all blood from the brain drains through
them into the IJV.
 The
superior sagittal sinus lies in the convex
attached border of the falx cerebri.
 It begins at the crista galli and ends near the
internal occipital protuberance at the
confluence of sinuses, a meeting place of the
superior sagittal, straight, occipital and
transverse sinuses.
 The
superior sagittal sinus receives the
superior cerebral vein and communicates on
each side through slit like openings with the
lateral venous lacunae-lateral expansions of
the superior sagittal sinus.
 The inferior sagittal sinus, much smaller than
the superior sagittal sinus, runs in the
inferior concave free border of the falx
cerebri and ends in the straight sinus.
 The
straight sinus is formed by the union of
the inferior sagittal sinus with the great
cerebral vein.
 It runs inferoposteriorly along the line of
attachment of the falx cerebri to the
tentorium cerebelli where it joins the
confluence of sinuses.
 The
transverse sinuses pass laterally from the
confluence of sinuses grooving the occipital
bones and the posteroinferior angles of
parietal bones.
 The transverse sinuses course along the
posterolateral attached margins of the
tentorium cerebelli and become sigmoid
sinuses as they approach the posterior
aspects of the petrous temporal bones.
 Blood
received by the confluence of sinuses
is drained by the transverse sinuses but
rarely equally.
 Usually the left sinus is dominant(larger).
 The sigmoid sinuses follow S-shaped courses
in the posterior cranial fossa forming deep
grooves in the temporal and occipital bones.
 Each
sigmoid sinus runs anteriorly and then
continues inferiorly as the IJV after
traversing the jugular foramen.
 The occipital sinus lies in the attached
border of the cerebellar falx and ends
superiorly in the confluence of sinuses.
 The occipital sinus communicates inferiorly
with the internal vertebral venous plexus.
 The
cavernous sinus/lateral sellar
compartment is situated bilaterally on each
side of the sella turcica on the upper surface
of the body of the sphenoid bone, which
contains the sphenoidal(air) sinus.
 Each sellar compartment contains a
cavernous sinus consisting of a venous plexus
of extremely thin walled veins.
 The
superior petrosal sinuses run from the
posterior ends of the veins comprising the
cavernous sinus to the transverse sinuses at
the site where these sinuses curve inferiorly
to form the sigmoid sinuses.
 Each superior petrosal sinus lies in the
anterolateral attached margin of the
tentorium cerebelli, which attaches to the
superior border of the petrous part of the
temporal bone.
 The
inferior petrosal sinuses also commence
at the posterior end of the cavernous sinus
inferiorly.
 Each inferior petrosal sinus runs in the
groove btwn the petrous part of temporal
bone and the basilar part of occipital bone.
 The inferior petrosal sinuses drain the veins
of the lateral cavernous sinus directly into
the origin of IJV.