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Venous Blood SinusesThey are blood-filled spaces situated
between the layers of the dura mater. They are lined by
endothelium. Their walls are thick and composed of fibrous tissue.
They have no muscular tissue. They have no valves. They receive
tributaries from the brain; the diploic veins of the skull; the
orbit and the internal ear. Inferior Sagittal Sinus It occupies the
free lower margin of the falx cerebri. It runs backward and joins
the great cerebral vein which is formed by the union of the 2
internal cerebral veins at the free margin of the tentorium
cerebelli to form the straight sinus. It receives cerebral veins
from the medial surface of the cerebral hemisphere. N.B: Veins have
no valves ; no muscular tissue in their wall and drain into venous
sinuses
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Superior Sagittal SinusIt occupies the upper fixed border of the
falx cerebri. It begins in the front at the foramen cecum where it
receives a vein from the nasal cavity. It runs backward, grooving
the vault of the skull and at the internal occipital protuberance
it deviates to one side ( usually the right ) and becomes
continuous with the transverse sinus.It communicates through small
openings with 2 or 3 venous lacunae on each side. Numerous
arachnoid villi and granulations project into these lacunae which
also receive the diploic; emissary and meningeal veins. It receives
the superior cerebral veins . At the internal occipital
protuberance it is dilated to form the confluence of the sinuses
which is connected to the opposite transverse sinus and receives
the occipital sinus.
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Straight SinusIt occupies the line of junction of the falx
cerebri with the tentorium cerebelli. It is formed by the union of
the inferior sagittal sinus with the great cerebral vein. It ends
by turning to the left ( sometimes to the right ) to form the
transverse sinus.
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Occipital SinusIt is a small sinus occupying the attached margin
of the falx cerebelli. It communicates with the vertebral veins
near the foramen magnum.Superiorly it drains into the confluence of
sinuses.
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Transverse SinusThey are paired and begin at the internal
occipital protuberance. The right sinus usually continuous with the
superior sagittal sinus. The left is continuous with the straight
sinus. Each sinus occupies the attached margin of the tentorium
cerebelli , grooving the occipital bone and posteroinferior angle
of the parietal bone. They receive the superior petrosal sinuses;
inferior cerebral and cerebellar veins and diploic veins. They end
by turning downward as the sigmoid sinuses.
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Superior and Inferior Petrosal SinusesThey are small and
situated on the superior and inferior borders of the petrous part
of the temporal bone on each side. Each superior sinus drains the
cavernous sinus into the transverse sinus.Each inferior sinus
drains the cavernous sinus into the internal jugular vein.
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Sigmoid SinusesThey are a direct continuation of the transverse
sinuses. Each sinus turns downward and medially and grooves the
mastoid part of the temporal bone. Here it lies behind the mastoid
antrum.It then turns downward through the posterior part of the
jugular foramen to become continuous with the superior bulb of the
internal jugular vein.
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Cavernous SinusesThey are situated in the middle cranial fossa
on each side of the body of the sphenoid bone. Each sinus extends
from the superior orbital fissure in front to the apex of the
petrous part of the temporal bone behind. The 3rd ; 4th cranial
nerves and the ophthalmic & maxillary divisions of the
trigeminal nerve run forward in the lateral wall of this sinus.
They lie between the endothelial and the dura mater . The internal
carotid artery, its sympathetic nerve plexus and abducent nerve run
forward through it. They are separated from the blood by an
endothelial covering.
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The tributaries are 1- Superior ophthalmic vein which
communicates it with the facial V 2- Inferior ophthalmic vein. 3-
Cerebral veins 4- Central vein of the retina 5- Sphenopareital
sinus. The sinus drains posteriorly into the superior and inferior
petrosal sinuses and inferiorly into the pterygoid venous
plexus.The 2 sinuses communicate with one another by means of the
anterior and posterior intercavernous sinuses which run in the
diaphragma sellae in front and behind the stalk of the hypophysis
cerebri.155
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Hypophysis CerebriThe pituitary gland is an edocrine gland. It
is small, oval and attached to the undersurface of the brain by
infundibulum.It is located in the sella turcica of the sphenoid
bone. It is divided into an anterior lobe or adenohypophysis and
posterior lobe or neurohypophysis. Relations Superiorly: The
diaphragma sellae which has a central aperture that allows the
passage of the infundibulum. This sellae separates the anterior
lobe from the optic chiasma. Inferiorly: The body of the sphenoid
with its sphenoid air sinuses. Laterally: The cavernous sinus and
its contents. Posteriorly: The dorsum sellae; basilar artery and
pons.Blood supply: The superior and inferior hypophyseal arteries
the branches of the internal carotid artery. Veins drain into the
intercavernous sinuses.
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Clinical Notes Hypophyseal enlargement and Optic chiasmaA
pituitary tumor pushes the diaphragma sellae upward and causes
pressure on the optic chiasma. This results in interference with
the function of the nerve fibers crossing in the chiasma ( from the
inner quadrants of the retina ) and the patient presents with
bitemporal hemianopia. Further expansion of the pituitary tumor
causes erosion of the body of the sphenoid bone.
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Extradural Hemorrhage
It results from injuries of the meningeal arteries or veins. The
most common is the anterior branch of the middle meningeal
artery.
A minor blow to the side of the head result in fracture of the
anteroinferior portion of the parietal bone ( pterion ).
The intracranial pressure rises. The blood clot exerts local
pressure on the underlying motor area in the precentral gyrus.
Blood may pass out through the fracture line to form a soft
swelling under the temporalis muscle.
The burr hole through the skull wall should be placed 2.5 to 4
cm above the midpoint of the zygomatic arch to ligate or plug the
torn artery or vein.
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Subdural Hemorrhage It is more common than the middle meningeal
artery hemorrhage. It results from tearing of the superior cerebral
veins at their entrance into the superior sagittal sinus. The cause
is a blow on the front or back of the head causing anteroposterior
displacement of the brain within the skull. Blood under low
pressure begins to accumulate in the space between the dura and
arachnoid. The case is bilateral in 50 %. Acute symptoms in the
form of vomiting due to rise in the venous pressure may be present.
In the chronic form, over a several months, the small blood clot
will attract fluid by osmosis so a hemorrhagic cyst is formed and
gradually expands produces pressure symptoms.
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Intracranial Hemorrhage in the Infant
It occurs during birth and from excessive molding of the head.
Bleeding occurs from cerebral veins or venous sinuses
Excessive anteroposterior compression often tears the anterior
attachment of the falx cerebri from the tentorium cerebelli.
bleeding then takes place from the great cerebral veins;
straight sinus or inferior sagittal sinus.
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Subarachnoid Hemorrahage
It results from leakage or rupture of a congenital aneurysm on
the circle of Willis or less commonly from an angioma.
The sudden symptoms include severe headache; stiffness of the
neck and loss of consciousness.
The diagnosis is established by withdrawing heavily blood-
stained CSF fluid through a lumbar puncture ( spinal tap ).
Cerebral Hemorrhage
It is caused rupture of the thin-walled lenticulostriate artery,
a branch of the middle cerebral artery. The hemorrhage involves the
vital corticobulbar & corticospinal fibers in the internal
capsule and produces hemiplegia on the opposite side of the body.
The patient immediately loses consciouness and paralysis is evident
when consciousness regained.