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Confluence of sinuses

The confluence of sinuses, also known as the torcular Herophili, is a critical anatomical structure located at the internal occipital protuberance, where several major dural venous sinuses converge. This venous junction serves as a central meeting point for the superior sagittal, straight, occipital, and transverse sinuses, facilitating the drainage of blood from the brain toward the systemic venous circulation. Understanding its imaging appearance is essential in neuroanatomy and neuroradiology.

Synonyms

  • Torcular Herophili

  • Confluens sinuum

  • Confluence of the sinuses

  • Torcular (informal, clinical usage)

Function

  • Acts as a major junction for venous drainage of the brain.

  • Receives venous blood from:

    • Superior sagittal sinus

    • Straight sinus

    • Occipital sinus

    • Transverse sinuses

  • Directs venous flow predominantly into the transverse sinuses.

  • Ensures efficient cerebral blood drainage and maintains intracranial pressure homeostasis.

MRI Appearance

T2-Weighted Images:

  • Appears as a flow void (dark/black signal) due to rapidly moving blood.

  • May see the adjacent sinuses joining as dark curvilinear structures.

  • No abnormal signal unless pathology (e.g., thrombosis).

T1-Weighted Images:

  • Normally low signal (hypointense) flow void, similar to other dural sinuses.

  • The margins of the confluence may be more conspicuous than on T2.

Phase Contrast (PC) 3D MRI:

  • Shows high signal within the sinus lumen reflecting flow.

  • Excellent for evaluating direction and velocity of blood flow.

  • Useful for detecting flow disturbances, stenosis, or absence of flow.

Post-Contrast T1-Weighted Images:

  • The confluence of sinuses enhances vividly due to the presence of blood and contrast medium.

  • Well-defined, symmetric enhancement.

  • Lack of enhancement or filling defects may suggest thrombus or mass.

CT Appearance

  • Seen as a hyperdense linear or triangular structure at the internal occipital protuberance (non-contrast CT).

  • On contrast-enhanced CT, shows intense homogeneous enhancement.

  • Bony anatomy (internal occipital protuberance) can help in localization.

  • Filling defects or lack of enhancement may indicate pathology (e.g., dural sinus thrombosis).

CTV (CT Venography) Appearance

  • Clearly delineates the confluence and draining sinuses as high-density contrast-filled structures.

  • Allows visualization of filling defects (suggestive of thrombus) or anatomical variants.

  • Useful for rapid assessment of venous sinus patency in acute settings.

MRI images

Confluence of sinuses MRI 3T axial image

MRI images

Confluence of sinuses MRI 3T coronal image

CT image

Confluence of sinuses ct