The sigmoid sinus (latin: sinus sigmoideus) is a S-shaped dural venous sinus that extends beneath the temporal bone from the mastoid process to the jugular foramen.
The sigmoid sinus is a continuation of the transverse sinuses, arising where the transverse sinus leaves the tentorium cerebelli. The sigmoid sinus passes inferomedially in a groove on the mastoid process of the temporal bone. Further, the sigmoid sinus crosses the jugular process of the occipital bone and passes forwards to the jugular foramen, continuing as the internal jugular vein.
The sigmoid sinus has connections with the pericranial veins through the mastoid and condylar emissary veins.