Sigmoid sinus
Sinus sigmoideus
An S-shaped dural venous sinus on the inside of the skull behind the ear, carrying blood from the transverse sinus to the jugular foramen.
At a glance
- English
- Sigmoid sinus
- Latin (TA2)
- Sinus sigmoideus
- System
- Vein
- Region
- Head
- Side
- Paired, left and right
About the sigmoid sinus
The sigmoid sinus takes its name from its S-shaped curve. It is the continuation of the transverse sinus at the point where that sinus leaves the attached edge of the tentorium cerebelli, near the base of the petrous part of the temporal bone. There is one on each side, and the right is usually larger, matching the larger right transverse sinus.
From its beginning the sinus turns downwards and medially in a deep groove on the inner surface of the mastoid part of the temporal bone, then curves forwards over the jugular process of the occipital bone. It ends at the jugular foramen, where it passes through the back part of the opening and becomes the superior bulb of the internal jugular vein. Just at its lower end it is joined by blood from the inferior petrosal sinus, which enters the jugular vein through the front part of the same foramen.
On its way it collects cerebellar and cerebral veins, diploic veins from the spongy bone of the skull and emissary veins. The mastoid emissary vein and the condylar emissary vein connect it with the occipital vein and the veins of the suboccipital region outside the skull. It is one of the main exits for blood draining the brain.
The sinus lies only a thin plate of bone away from the mastoid air cells, so infection of the middle ear and mastoid can spread to it and cause sigmoid sinus thrombosis. Surgeons drilling the mastoid must identify it to avoid tearing it, and its position limits approaches to the back of the skull. A forward-lying or unusually large sinus can also cause pulsatile tinnitus.
Course and drainage
- Begins at
- Continues from the transverse sinus where that sinus leaves the tentorium near the base of the petrous temporal bone.
- Drains into
- Passes through the jugular foramen to become the superior bulb of the internal jugular vein.
- Drains
- Carries blood from the transverse sinus and drains cerebellar, cerebral, diploic and emissary veins on the way to the internal jugular vein.
Anthromica
See the sigmoid sinus where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
