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Interpeduncular fossa

The interpeduncular fossa is a deep, triangular depression located at the base of the brain, lying between the cerebral peduncles of the midbrain. This region is a critical anatomical landmark, forming part of the basal cisterns and providing passage for several important neurovascular structures. It serves as an access point for cerebrospinal fluid flow around the midbrain and contains key elements such as the posterior perforated substance and portions of the circle of Willis.

Synonyms

  • Basal cistern between cerebral peduncles

  • Fossa interpeduncularis (Latin)

  • Interpeduncular cistern (when referring to its CSF-filled nature)

  • Midbrain cistern (less commonly used)

Function

  • Acts as a passage and reservoir for cerebrospinal fluid (CSF) as part of the basal cistern system

  • Provides a protective space for the oculomotor nerve (CN III), posterior cerebral arteries, and perforating branches of the circle of Willis

  • Contains the posterior perforated substance, which allows for entry of small penetrating arteries into the brainstem

  • Facilitates vascular supply and drainage around the midbrain region

  • Serves as an important neurosurgical and neuroimaging landmark

MRI Appearance

T2-weighted images:

  • Appears as a CSF-intensity (hyperintense) space between the cerebral peduncles

  • Clearly delineates the triangular fossa and adjacent vascular/nerve structures

  • Vessels and nerves may be seen as hypointense linear or dot-like structures within the fossa

T1-weighted images:

  • Shows the fossa as a CSF-intensity (hypointense) area at the base of the midbrain

  • Posterior perforated substance appears slightly more hyperintense compared to CSF

  • Vascular structures may enhance if contrast is used

FLAIR images:

  • Normally, the CSF within the interpeduncular fossa is suppressed (dark)

  • Pathological processes (e.g., blood, pus, tumors) will appear hyperintense against the dark background of suppressed CSF

CT Appearance

  • The interpeduncular fossa appears as a low-density (hypodense) triangular space between the midbrain peduncles

  • Normal vessels may be seen as faint linear or dot-like hyperdensities if calcified or in the presence of acute hemorrhage

  • Easily obscured in cases of cisternal blood, mass effect, or significant brain swelling

  • Useful for detecting acute hemorrhage or subarachnoid blood pooling in the basal cisterns

MRI images

Interpeduncular fossa mri 3t axial image