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Inferior petrosal sinus

The Inferior Petrosal Sinus (IPS) is a paired dural venous sinus located at the skull base. It courses along the groove between the petrous part of the temporal bone and the basilar part of the occipital bone, extending from the posterior cavernous sinus to the jugular bulb. The IPS is an important venous channel for draining blood from the cavernous sinus into the internal jugular vein. Understanding its anatomy and imaging appearance is crucial, especially in the context of venous sampling procedures and the evaluation of skull base lesions.

Synonyms

  • IPS

  • Sinus petrosus inferior

  • Inferior petrosal venous sinus

  • Petrosal sinus (when context is clear)

Function

  • Drains venous blood from the cavernous sinus to the internal jugular vein.

  • Plays a key role in cerebral venous outflow, especially from the central skull base.

  • Frequently used in inferior petrosal sinus sampling (IPSS) for diagnosing Cushing's disease (pituitary ACTH source localization).

MRI Appearance

  • T1-Weighted Images

    • Appears as a linear or tubular structure, typically isointense or mildly hypointense to brain parenchyma before contrast.

    • Sometimes not well visualized unless thrombosed or enlarged.

  • T2-Weighted Images

    • Usually flow void is seen in normal IPS due to high-velocity venous flow (signal loss, appearing dark).

    • Slow flow or thrombosis may cause increased signal (hyperintense).

  • 3D Phase-Contrast (PC) MR Venography

    • Clearly delineates the IPS as a high-flow venous structure.

    • Demonstrates continuity with the cavernous sinus and jugular bulb.

    • Useful for anatomical mapping prior to venous interventions.

  • Post-Contrast T1-Weighted Images (Gadolinium-enhanced)

    • IPS enhances strongly and uniformly with intravenous contrast.

    • Enhancement helps differentiate IPS from adjacent soft tissues and cranial nerves.

    • Can reveal filling defects in the case of thrombosis or invasion by tumor.

CT Appearance

  • Non-contrast CT

    • IPS itself is usually not well visualized as a distinct structure.

    • May be seen as a low-density line in the petro-occipital fissure region in high-resolution scans.

  • CT Venography (CTV)

    • IPS appears as an enhancing linear or tubular venous structure along the inferior petrosal sulcus.

    • Best seen on post-contrast images, especially with thin-section or 3D reconstructions.

MRI images

Inferior petrosal sinus MRI 3T axial image

MRI images

Inferior petrosal sinus MRI 3T coronal image