Base Of The Peduncle Of The Brainstem

Description

Cerebral peduncles (pedunculi cerebri) dominate the ventral aspect of the midbrain, forming the broad, convex base of the brainstem known as the basis pedunculi (crura cerebri). Each peduncle sits lateral to the interpeduncular fossa at the midline, with the paired columns converging superiorly toward the diencephalon and diverging inferiorly toward the pontomesencephalic junction. Medially, the oculomotor nerve (CN III) rootlets typically emerge from the interpeduncular region between the peduncles, a useful landmark when orienting the ventral mesencephalon in gross anatomy. Major descending motor pathways course here. Clinically, the basis pedunculi matters because it concentrates corticospinal, corticobulbar, and corticopontine fibers in a compact anterolateral bundle, so small paramedian perforator infarcts can produce dense contralateral hemiparesis and dysarthria out of proportion to lesion size. Lesions that extend dorsally toward the tegmentum can combine peduncular weakness with ipsilateral CN III palsy (classically Weber syndrome), tying ventral midbrain surface anatomy to bedside localization. The fixed ventral perspective is also the one surgeons and neuroradiologists mentally reference when tracking the relationship between the peduncle, interpeduncular cistern, and the posterior cerebral and superior cerebellar arteries that curve around the midbrain. Use this illustration in medical neuroanatomy curricula to anchor the external landmarks of the mesencephalon, in stroke education materials illustrating ventral midbrain syndromes, or in operative anatomy chapters discussing approaches that traverse the interpeduncular cistern and risk injury to CN III and adjacent perforators. Anatomical accuracy verified by SciePro's Medical Advisory Board.