Interpeduncular Fossa Of The Brainstem

Description

Interpeduncular fossa anatomy centers on the anterior midbrain, where the left and right cerebral peduncles (crura cerebri) diverge to form a diamond-shaped depression on the ventral surface of the brainstem. Superior to the fossa, the hypothalamic region comes into view, with the mammillary bodies typically forming a paired, rounded landmark just rostral to the posterior perforated substance. Inferiorly, the ventral pons aligns in the midline beneath the peduncles, while the floor of the fossa corresponds to the posterior perforated substance, a perforated field for penetrating branches that enter the midbrain. Oculomotor nerve rootlets (CN III) emerge from the medial aspect of each peduncle, bordering the fossa on either side. Small space, high density. This anterior perspective matters because it fixes the spatial relationship between CN III, the cerebral peduncles, and the paramedian perforators that arise near the basilar apex and posterior cerebral circulation, a common zone for aneurysms and subarachnoid hemorrhage patterns. The interpeduncular region also helps explain clinical localization: compression of CN III against the peduncle can present with ptosis, mydriasis, and ophthalmoplegia, while adjacent peduncular involvement supports midbrain syndromes such as Weber syndrome with contralateral hemiparesis. Crisp separation of midbrain, hypothalamic landmarks, and the superior pons makes it easier to teach where “ventral midbrain” ends and “ventral pons” begins without relying on sectional anatomy. Neuroanatomy and neurosurgery courses can use this illustration when introducing the ventral brainstem, cranial nerve emergence, and perforator-rich cisternal anatomy around the interpeduncular cistern. It also fits well in clinical atlases discussing aneurysms at the basilar bifurcation or posterior communicating artery and their relationship to the oculomotor nerve in an anterior brainstem orientation. Anatomical accuracy verified by SciePro's Medical Advisory Board.