Posterosuperior Group
Superior Sagittal Sinus (SSS). The superior sagittal sinus traverses the superior margin of the falx cerebri, gradually increasing in dimension as it passes posteriorly, receiving superior cerebral veins and veins from the pericranium, the diploe, and dura mater. Its anterior portion is occasionally absent, replaced by two veins converging behind the coronal suture. The SSS terminates near the occipital protuberance and joins the straight sinus to form the confluence of sinuses (torcular herophili).
Inferior Sagittal Sinus (ISS). The inferior sagittal sinus traverses the posterior two thirds of the lower falx cerebri margin; this becomes larger as it receives veins from the falx and cerebral hemisphere’s medial surfaces to join the great cerebral vein of Galen, forming the straight sinus.
Straight Sinus. The straight sinus is located at the falx cerebri junction with the tentorium cerebelli, receiving superior cerebellar veins to terminate and join the confluence of sinuses. It is usually a single channel, although occasionally doubled or tripled.
Transverse Sinuses (bilateral; usually of unequal size). The transverse sinuses are at the internal occipital protuberance, where usually the right side is the direct SSS continuation, whereas the other derives from the straight sinus. Each becomes larger running anterolaterally within the tentorium cerebelli margin, receiving the superior petrosal sinuses, and inferior cerebral, cerebellar, diploic, condyloid, and mastoid veins. These leave the tentorium, entering the jugular foramen as the sigmoid sinus.
Sigmoid Sinuses. Sigmoid sinuses are continuations of the transverse sinuses situated over the temporal mastoid bones. These terminate at the jugular foramens, draining into the internal jugular veins.
Occipital Sinus. The occipital sinus is the smallest, usually single, sinus, originating from small venous channels at the foramen magnum, communicating with the transverse sinus, and terminating at the confluence of the sinuses.
Anteroinferior Group
Cavernous Sinuses. Cavernous sinuses are irregular networks of communicating venous channels beginning at the superior orbital fissures and extending to the petrous apex of the temporal bones. The internal carotid artery, carotid plexus, and abducens nerve lie on its medial wall, whereas oculomotor, trochlear, and ophthalmic/maxillary divisions of trigeminal nerves traverse the lateral wall. Each sinus receives ophthalmic (superior and inferior) and middle cerebral veins and the small sphenoparietal sinus, and it communicates via the intercavernous sinuses. These drain into the transverse sinuses via the superior petrosal sinuses, the internal jugular veins via the inferior petrosal sinuses, the plexus of veins on the internal carotid artery, and the pterygoid venous plexus.
Intercavernous Sinuses. Anterior and posterior sinuses connect the two cavernous sinuses, forming a venous circle around the pituitary stalk.
Sphenoparietal Sinuses. They course along the undersurface of the lesser wing of the sphenoid bone and drain into the cavernous sinuses.
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