Topics

Topic

design image
Sigmoid sinus

The sigmoid sinus is a dural venous sinus located within the posterior cranial fossa. It plays a crucial role in draining blood from the brain, acting as the continuation of the transverse sinus and terminating in the jugular bulb, ultimately forming the internal jugular vein. The sigmoid sinus courses in an S-shaped (sigmoid) curve along the temporal and occipital bones. Due to its anatomical location and function, it is frequently evaluated in neuroimaging, especially in the context of thrombosis, tumors, or post-surgical changes.

Synonyms:

  • Lateral sinus (historic, now less used)

  • S-shaped dural sinus

Function:

  • Drains venous blood from the transverse sinus to the internal jugular vein

  • Receives blood from cerebellar and brainstem veins, mastoid and condylar emissary veins

  • Critical pathway for cerebral venous return and intracranial pressure regulation

MRI Appearance:

  • T2-Weighted Images:

    • Normal sigmoid sinus shows flow void (appears as a black/dark structure due to rapid blood flow)

    • Absence of flow void may suggest thrombosis or slow flow

  • T1-Weighted Images:

    • Normally hypointense to isointense compared to brain parenchyma

    • Acute thrombus may appear hyperintense or isointense, subacute thrombus may show increased signal

  • PC 3D (Phase Contrast 3D):

    • Clearly demonstrates venous blood flow within the sinus as a high-signal intensity channel

    • Useful for assessing patency and identifying flow abnormalities

  • Post-Contrast T1 (T1 + Gadolinium):

    • Sigmoid sinus enhances strongly and homogeneously

    • Non-enhancing filling defect or absent enhancement may indicate thrombosis

    • Adjacent meningeal or soft tissue enhancement may suggest infection or tumor

CT Appearance:

  • Non-contrast CT:

    • Seen as a well-defined, airless, curvilinear structure posterior and lateral to the mastoid air cells

    • Hyperdense appearance may indicate acute thrombosis (dense sinus sign)

    • Bony groove or canal can often be visualized

CTV Appearance (CT Venography):

  • Sigmoid sinus appears as a well-opacified, curvilinear vascular structure

  • Filling defects, non-opacification, or irregular margins are suggestive of thrombosis

MRI images

Sigmoid sinus MRI 3T axial image

MRI images

Sigmoid sinus MRI 3T coronal image

MRI images

Sigmoid sinus MRI 3T sagittal pc image