Venous Sinuses

Superior sagittal sinus

Position

• Between the inner dura and the outer endosteum
• Begins above the foramen caecum
• Runs between the layers of the falx cerebri, backwards, and grooves the skull vault
• Deviates at the internal occipital protuberance

• Becomes continuous with the transverse sinus on whichever side it deviates too (typically the right)

• There is a slight dilation at this joining of the sinuses

Functions

• Drains the upper surface of the cerebral hemispheres 
• Receives the superior cerebral veins
• Contains arachnoid villi through which CSF is absorbed into the bloodstream

• NB: the rate of CSF production is independent of intracranial pressure across the normal range but the rate of absorption is dependent on ICP

Inferior sagittal sinus

• At the lower free margin of the falx cerebri
• Travels backwards to join the great cerebral vein
• Together they form the straight sinus 

Function

• Drains the lower parts of the medial surface of each hemisphere

Straight sinus

• Formed by inferior sagittal sinus and great cerebral vein (of Galen)
• Also receives the left and right basilar veins
• Runs backwards to drain into the transverse sinus (usually the left)

Transverse sinus

• Paired structure
• Lies between the inner dura and outer endosteum

• As above, the right is usually continuous with the superior sagittal sinus and the left with the straight sinus

Sigmoid sinuses

• Continuations of the transverse sinuses
• Grooves the mastoid part of the temporal bone

• Become continuous with the internal jugular vein
• The internal jugular
• Separated from the sympathetic chain by the prevertebral fascia
• Lies anterolateral to the sympathetic chain
• Separated from the inferior petrosal sinus by the 9th, 10th and 11th cranial nerves

Occipital sinus

• A small sinus at the margin of the falx cerebri

Cavernous sinus

Position

• In the middle cranial fossa on each side of the body of the sphenoid and the sella turcica 

• Extends from the superior orbital fissure anteriorly to the apex of the temporal bone posteriorly

• The interior is crossed by trabeculae
• Formed by layers of dura
• Internal carotid with sympathetic plexus and abducens nerve run along the floor

• CNs III, IV, V1 and V2 run in the lateral wall (in that order from top to bottom) between the endothelial lining and the dura

Functions

• Receives
• Superior ophthalmic vein
• Inferior ophthalmic vein (but this usually drains directly into superior)

• NB: the facial veins indirectly communicate with the sinuses via the superior and inferior ophthalmic veins

• Sphenoparietal sinus
• Inferior and superficial middle cerebral veins

• Drains into the superior and inferior petrosal sinuses posteriorly and the pterygoid venous plexus inferiorly.