Thecortical veins from the lateral surface of the temporal lobe may drain into the transverse sinus, but before entering it, theycommonly pass medially below the hemisphere to join a short sinus in thetentorium, which courses within the tento-rium for approximately 1 cm beforedraining into the terminal part of the transverse sinus. Thecortical veins from the basal surface of the temporal and occipital lobes usually join the lateral tentorial sinus. The vein of Labbécommonly ends in the transverse sinus, but may curve around the inferior marginof the hemisphere to join the lateral tentorial sinus. The transverse sinus maycommunicate through emissary veins in the occipital bone with the extracranialveins.
OccipitalsinusTheoccipital sinus (fig 7) is the smallest of the cranial sinuses. It is situatedin the attached margin of the falx cerebelli, and is generally single, butoccasionally There are two. Itcommences around the margin of the foramen magnum by several small venouschannels, one of which joins the terminal part of the transverse sinus; itcommunicates with the posterior internal vertebral venous plexuses and ends inthe confluence of the sinuses. (21) Fig7 showing occipital venous sinus in relation to other venous sinuses(30) TentorialSinusesEachhalf of the tentorium has two constant but rarely symmetrical venous channels, · themedial and · Lateraltentorial sinuses.(16)Ø The medial tentorial sinuses are formed by the convergence of veinsfrom the superior surface of the cerebellum, The medial tentorial sinusescourse medially to empty into the straight sinus or the junction of thestraight and Transverse sinuses.
Ø The lateral tentorial sinuses are formed by the convergence ofveins from the basal and lateral surfaces of the temporal and occipital lobes.The lateral tentorial sinuses arise within the lateral part of the tentoriumand Course laterally to drain into the terminal portion of the transverse sinus. Fig 8 Direct superior of the LTS. 1, anterior temporal vein; 2, anteriortemporobasal vein; 3, middle temporobasal vein; 4, posterior temporobasal vein;5, occipitobasal vein; 6, posterior temporal vein; 7, vein of Labbé; 8, middletemporal vein. (20) Fig 9 showing both LTS,MTS in relation to surrounding structures (16) Cavernous SinusThe paired cavernous sinuses are situated on each side of the sellaturcica and are connected across the midline by the anterior and posterior intercavernoussinuses, which course in the junction of the diaphragma sellae with the duralining thesella.
(16)ØAnteriorly,each cavernous sinus communicates with the sphenoparietal sinus and theophthalmic veins.ØIts middleportion communicates through a lateral extension on the inner surface of thegreater sphenoid wing with the pterygoid plexus via small veins that passthrough the foramina spinosum and ovale. ØPosteriorly,the cavernous sinus opens directly into the basilar sinus, which sits on theclivus.
It communicates through the superior petrosal sinus with the junctionof the transverse and sigmoid sinuses and through the inferior petrosal sinuswith the sigmoid sinus. Fig 10 showing cavernous sinus in relation to surrownding structures (15) Fig 11 showing contentsof cavernous Sinus (17) SuperiorPetrosal Sinusü The superior petrosal sinus (fig 12) courses within the attachment ofthe 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 sigmoidsinuses.
ü The bridging veins that join it usually arise from the cerebellumand brainstem, not the cerebrum.ü The sinus may course over, under, or around the posterior root ofthe trigeminal nerve. ü The superficial sylvian veins may empty into an infrequenttributary of the superior petrosal sinus called the sphenopetrosal sinus.Inferiorpetrosal sinusü Inferior petrosal sinuses(fig 12) aresmall sinuses situated on the inferior border of the petrous part of thetemporal bone on each side (16).ü Each inferior petrosal sinus drains the cavernous sinus into theinternal jugular vein.
ü The inferior petrosal sinus is situated in the inferior petrosalsulcus, formed by the junction of the petrous part of the temporal bone withthe 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 superiorbulb of the internal jugular vein.ü The inferior petrosal sinus receives the internal auditory veinsand also veins from the medulla oblongata, pons, and under surface of thecerebellum. Fig 12 showingsuperior and inferior petrosal sinuses (18) Sphenoparietal,Sphenobasal, and Sphenopetrosal SinusesThesphenoparietal sinus is the largest of the meningeal channels coursing with themeningeal arteries.
Fig (9)It accompaniesthe anterior branch of the middle meningeal artery above the level of thepterion. Below this level, it deviates from the artery and courses in the duramater just below the sphenoid ridge to empty into the anterior part of theCavernoussinus. Itsupper end communicates through the meningeal veins with the superior sagittalsinus. Thesinus coursing along the sphenoid ridge may turn inferiorly to reach the floorof the middle cranial fossa rather than emptying into the anterior part of thecavernous sinus. From here, it courses posteriorly to empty into a lateralextension of the cavernous sinus on the greater sphenoid wing or joins thesphenoidal emissary veins, which pass through the floor of the middle fossa toreach the pterygoid plexus. It also may pass further posteriorly to join thesuperior petrosal or lateral sinuses.
ü The variant in which thesinus exits the cranium by joining the sphenoidal emissary veins and thepterygoid plexus is referred to as the sphenobasal sinus, ü the variant in which the sinus courses further posteriorly alongthe floor of the middle fossa and drains into the superior petrosal or lateral sinusis called the sphenopetrosal sinus. The superficial sylvian veinscommonly empty into the sphenoparietal sinus. If the sphenoparietal sinus isabsent or poorly developed, the sylvian veins may drain directly into the cavernoussinus or they may turn inferiorly around the anterior pole and inferior surfaceof the temporal lobe to empty into the sphenobasal or sphenopetrosal sinuses.(16)