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Occipital sinus

The occipital sinus is the smallest and most variable of the dural venous sinuses. It runs along the attached margin of the falx cerebelli, situated in the posterior cranial fossa, and typically drains into the confluence of sinuses. Although often diminutive or even absent in many adults, its identification is important in radiological practice, especially in cases of venous anatomical variants, pediatric populations, or posterior fossa surgery planning.

Synonyms:

  • Sinus occipitalis (Latin)

  • Dural occipital sinus

Function:

  • Drains venous blood from the cerebellum and inferior aspects of the posterior cranial fossa

  • Connects the confluence of sinuses with the marginal sinus at the foramen magnum

  • May provide collateral venous drainage, especially in cases of transverse or sigmoid sinus hypoplasia/atresia

MRI Appearance:

  • T2-weighted MRI:

    • The occipital sinus appears as a linear or tubular flow void along the midline, posterior to the cerebellum, due to rapid venous flow.

    • Signal void may be subtle, especially if the sinus is small or partially thrombosed.

  • T1-weighted MRI:

    • Similar to T2, the sinus appears as a low-signal intensity linear structure (flow void) within the dura along the falx cerebelli.

    • Difficult to visualize if the sinus is very small or absent.

  • 3D Phase Contrast (PC 3D) MRI:

    • Highly sensitive for venous structures; the occipital sinus is best visualized as a small, enhancing venous channel along the midline posterior fossa.

    • Useful for detecting patency and assessing venous flow direction.

  • Post-contrast T1-weighted MRI:

    • Enhances and clearly delineates the occipital sinus as a thin, enhancing linear structure.

    • Enhancement is due to intraluminal contrast filling.

    • Best visualized with high-resolution and thin-slice imaging.

CT and CTV Appearance:

  • Non-contrast CT:

    • Typically not visible due to small size and lack of natural contrast with surrounding structures.

    • Rarely, a hyperdense linear structure may be seen if there is thrombosis.

  • CT Venography (CTV):

    • The occipital sinus appears as a small, contrast-filled venous channel posterior to the cerebellum and along the falx cerebelli.

    • More easily identified with thin-section and multiplanar reformatted images.

MRI images

Occipital sinus MRI 3T axial image

MRI images

Occipital sinus MRI 3T coronal image