Home Research PapersThe rarely symmetrical venous channels, · the medial and

The rarely symmetrical venous channels, · the medial and

The
cortical veins from the lateral surface of the temporal lobe may drain into the transverse sinus, but before entering it, they
commonly pass medially below the hemisphere to join a short sinus in the
tentorium, which courses within the tento-rium for approximately 1 cm before
draining into the terminal part of the transverse sinus.

 

The
cortical veins from the basal surface of the temporal and occipital lobes usually join the lateral tentorial sinus. The vein of Labbé
commonly ends in the transverse sinus, but may curve around the inferior margin
of the hemisphere to join the lateral tentorial sinus. The transverse sinus may
communicate through emissary veins in the occipital bone with the extracranial
veins.

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Occipital
sinus

The
occipital sinus (fig 7) is the smallest of the cranial sinuses. It is situated
in the attached margin of the falx cerebelli, and is generally single, but
occasionally

 There are two.

 

It
commences around the margin of the foramen magnum by several small venous
channels, one of which joins the terminal part of the transverse sinus; it
communicates with the posterior internal vertebral venous plexuses and ends in
the confluence of the sinuses. (21)

 

Fig
7 showing occipital venous sinus in relation to other venous sinuses
(30)

 

Tentorial
Sinuses

Each
half of the tentorium has two constant but rarely symmetrical venous channels,

·       
the
medial and

·       
Lateral
tentorial sinuses.(16)

Ø The medial tentorial sinuses are formed by the convergence of veins
from the superior surface of the cerebellum, The medial tentorial sinuses
course medially to empty into the straight sinus or the junction of the
straight and Transverse sinuses.

Ø The lateral tentorial sinuses are formed by the convergence of
veins from the basal and lateral surfaces of the temporal and occipital lobes.
The lateral tentorial sinuses arise within the lateral part of the tentorium
and Course laterally to drain into the terminal portion of the transverse sinus.

Fig 8 Direct superior of the LTS. 1, anterior temporal vein; 2, anterior
temporobasal vein; 3, middle temporobasal vein; 4, posterior temporobasal vein;
5, occipitobasal vein; 6, posterior temporal vein; 7, vein of Labbé; 8, middle
temporal vein. (20)

Fig 9 showing both LTS,
MTS in relation to surrounding structures (16)

 

 

Cavernous Sinus

The paired cavernous sinuses are situated on each side of the sella
turcica and are connected across the midline by the  anterior and posterior intercavernous
sinuses, which course in the junction of the diaphragma sellae with the dura
lining the

sella. (16)

Ø
Anteriorly,
each cavernous sinus communicates with the sphenoparietal sinus and the
ophthalmic veins.

Ø
Its middle
portion communicates through a lateral extension on the inner surface of the
greater sphenoid wing with the pterygoid plexus via small veins that pass
through the foramina spinosum and ovale.

Ø
Posteriorly,
the cavernous sinus opens directly into the basilar sinus, which sits on the
clivus. It communicates through the superior petrosal sinus with the junction
of the transverse and sigmoid sinuses and through the inferior petrosal sinus
with the sigmoid sinus.

Fig 10 showing cavernous sinus in relation to surrownding

 structures (15)

Fig 11 showing contents
of cavernous Sinus (17)

 

 

 

Superior
Petrosal Sinus

ü The superior petrosal sinus (fig 12) courses within the attachment of
the tentorium to the petrous ridge (16).

ü Its medial end connects with the posterior end of the cavernous sinus.

ü its lateral end joins the junction of the transverse and sigmoid
sinuses.

 

ü The bridging veins that join it usually arise from the cerebellum
and brainstem, not the cerebrum.

ü The sinus may course over, under, or around the posterior root of
the trigeminal nerve.

ü The superficial sylvian veins may empty into an infrequent
tributary of the superior petrosal sinus called the sphenopetrosal sinus.

Inferior
petrosal sinus

ü Inferior petrosal sinuses
(fig 12) are
small sinuses situated on the inferior border of the petrous part of the
temporal bone on each side (16).

ü Each inferior petrosal sinus drains the cavernous sinus into the
internal jugular vein.

ü The inferior petrosal sinus is situated in the inferior petrosal
sulcus, formed by the junction of the petrous part of the temporal bone with
the basilar part of the occipital bone.

ü It begins in the postero-inferior part of the cavernous sinus and,
passing through the anterior part of the jugular foramen, ends in the superior
bulb of the internal jugular vein.

ü The inferior petrosal sinus receives the internal auditory veins
and also veins from the medulla oblongata, pons, and under surface of the
cerebellum.

 

Fig 12 showing
superior and inferior petrosal sinuses (18)

 

 

Sphenoparietal,
Sphenobasal, and Sphenopetrosal Sinuses

The
sphenoparietal sinus is the largest of the meningeal channels coursing with the
meningeal arteries. Fig (9)

It accompanies
the anterior branch of the middle meningeal artery above the level of the
pterion. Below this level, it deviates from the artery and courses in the dura
mater just below the sphenoid ridge to empty into the anterior part of the

Cavernous
sinus.

Its
upper end communicates through the meningeal veins with the superior sagittal
sinus.

 

The
sinus coursing along the sphenoid ridge may turn inferiorly to reach the floor
of the middle cranial fossa rather than emptying into the anterior part of the
cavernous sinus. From here, it courses posteriorly to empty into a lateral
extension of the cavernous sinus on the greater sphenoid wing or joins the
sphenoidal emissary veins, which pass through the floor of the middle fossa to
reach the pterygoid plexus. It also may pass further posteriorly to join the
superior petrosal or lateral sinuses.

 

ü The  variant in which the
sinus exits the cranium by joining the sphenoidal emissary veins and the
pterygoid plexus is referred to as the sphenobasal sinus,

ü the variant in which the sinus courses further posteriorly along
the floor of the middle fossa and drains into the superior petrosal or lateral sinus
is called the sphenopetrosal sinus.

 

The superficial sylvian veins
commonly empty into the sphenoparietal sinus. If the sphenoparietal sinus is
absent or poorly developed, the sylvian veins may drain directly into the cavernous
sinus or they may turn inferiorly around the anterior pole and inferior surface
of the temporal lobe to empty into the sphenobasal or sphenopetrosal sinuses.
(16)

 

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