Overview

Structure. The sinuses lie between the outer (periosteal) and inner (meningeal) layers of the dura. Their walls are rigid and contain no smooth muscle, so they do not collapse. They have no valves.

Main drainage route. The superior sagittal sinus runs in the attached upper edge of the falx cerebri. Arachnoid granulations project into it and return CSF to the blood. It drains to the confluence of the sinuses at the internal occipital protuberance, and from there into the transverse sinuses (usually the right). Each transverse sinus continues as an S-shaped sigmoid sinus, which becomes the internal jugular vein at the jugular foramen.

Deep drainage. The inferior sagittal sinus runs in the free lower edge of the falx. It joins the great cerebral vein (of Galen) to form the straight sinus, which runs along the junction of the falx and tentorium to the confluence (usually draining to the left transverse sinus).

Cavernous sinuses. These lie on either side of the sella turcica. They receive the ophthalmic veins and drain through the superior and inferior petrosal sinuses. The internal carotid artery and CN VI pass through the sinus itself. CN III, IV, V1 and V2 run in its lateral wall.

Emissary veins. Valveless emissary veins connect the sinuses with veins of the scalp and face, so infection can spread inward.

Location: Inside the skull, between the layers of the dura mater: along the falx cerebri, the tentorium cerebelli and the skull base.

Parts & subdivisions

Superior sagittal sinus
Runs along the attached margin of the falx cerebri. It receives the superior cerebral (bridging) veins and the arachnoid granulations.
Inferior sagittal and straight sinuses
Drain the deep brain through the great cerebral vein to the confluence.
Transverse and sigmoid sinuses
Run from the confluence to the jugular foramen. The sigmoid sinus lies against the back of the mastoid air cells.
Cavernous sinus
Lies on each side of the pituitary fossa. It contains the internal carotid artery and CN VI, with CN III, IV, V1 and V2 in its lateral wall.
Petrosal and occipital sinuses
Smaller sinuses that link the cavernous sinus to the transverse and sigmoid sinuses or the internal jugular vein, and drain the posterior fossa.

Function

Drain venous blood from the brain, meninges, skull and orbit to the internal jugular veins.
Return cerebrospinal fluid to the blood through the arachnoid granulations.

Clinical significance

Cerebral venous sinus thrombosis

Cerebral venous sinus thrombosis typically affects young women. Risk factors include pregnancy and the period after childbirth, the oral contraceptive pill, thrombophilia, dehydration and infection. It causes headache, papilloedema, seizures and venous infarcts that often bleed. On contrast CT, the clot in the superior sagittal sinus can show as an "empty delta" sign. It is treated with anticoagulation.

Cavernous sinus thrombosis

Infection from the "danger triangle" of the face can spread through the valveless facial and ophthalmic veins to the cavernous sinus. Patients have fever, bulging eyes (proptosis), swollen conjunctiva, painful paralysis of eye movements (CN VI often first) and reduced sensation in the V1 and V2 areas.

Subdural haematoma

Bridging veins that cross the subdural space to reach the superior sagittal sinus can tear. This is especially likely in elderly people and people with alcohol dependence, whose brains have shrunk, and in shaken infants. The result is a crescent-shaped subdural haematoma.

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.