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Venous plexus of hypoglossal canal

The venous plexus of the hypoglossal canal is a network of small veins situated within the hypoglossal canal, an anatomical passage in the occipital bone that transmits the hypoglossal nerve (cranial nerve XII). This plexus forms a critical venous connection between the internal jugular vein system and the intracranial venous sinuses, specifically the sigmoid and inferior petrosal sinuses. The venous plexus serves as an important route for venous drainage of the posterior cranial fossa, and its anatomical variants and prominence can have implications for neurosurgical procedures and the spread of pathology.

Synonyms

  • Hypoglossal venous plexus

  • Plexus venosus canalis nervi hypoglossi

  • Hypoglossal canal venous plexus

Function

  • Provides venous drainage from the posterior cranial fossa to the internal jugular vein.

  • Acts as a potential collateral route for cerebral venous outflow, especially when primary routes are compromised.

  • May play a role in the spread of infection or tumor between intracranial and extracranial compartments due to its connections.

MRI Appearance

  • T2-Weighted MRI

    • Appears as a flow void (dark linear or dot-like signal) within the hypoglossal canal, indicating fast-moving blood.

    • Surrounding structures (bone, CSF, nerves) may provide anatomical context.

    • Sometimes, if flow is slow or thrombosed, the signal may appear hyperintense (bright).

  • T1-Weighted MRI

    • Typically, the venous plexus appears as a low signal intensity (dark) structure within the hypoglossal canal.

    • The hypoglossal nerve itself is isointense or slightly hyperintense to muscle.

  • 3D Phase Contrast (PC) MRI

    • Demonstrates flow-sensitive signal within the plexus.

    • Shows continuity with adjacent venous structures.

    • Useful for identifying direction and pattern of venous flow.

  • Post-Contrast T1-Weighted MRI

    • Shows enhancement of the venous plexus due to contrast opacification.

    • The plexus appears as a thin, enhancing linear or tubular structure within the canal.

    • Helps differentiate veins from non-enhancing nerves or pathological tissue.

CT and CTV Appearance

  • Non-Contrast CT

    • The venous plexus itself is not usually visible, but the hypoglossal canal can be identified as a bony canal in the occipital bone.

    • Occasionally, prominent veins may cause subtle lucency or fullness within the canal.

  • CT Venography (CTV)

    • The venous plexus enhances and can be visualized as a small, enhancing linear or tubular structure within the hypoglossal canal.

    • Demonstrates connections to the internal jugular vein or adjacent venous sinuses.

    • Useful for preoperative planning and for distinguishing normal veins from pathologic processes (e.g., dural arteriovenous fistula, venous sinus thrombosis).

MRI images

Venous plexus of hypoglossal canal MRI 3T coronal image

MRI images

Venous plexus of hypoglossal canal MRI 3T sagittal image