Crus Cerebri Of The Brainstem, Superior View

Description

Crus cerebri (basis pedunculi) dominates the superior aspect of the mesencephalon in this image, appearing as paired, broad white matter bundles on the anterolateral midbrain. Each cerebral peduncle lies lateral to the interpeduncular fossa, and the two peduncles angle medially as they converge toward the caudal brainstem. At their dorsal boundary, the crus transitions into the midbrain tegmentum, where the substantia nigra forms a clinically meaningful plane separating descending motor fibers from more posterior midbrain nuclei and ascending pathways. Orientation is unmistakable. These relationships matter because the crus cerebri carries corticospinal, corticobulbar, and corticopontine tracts, and small lesions here produce dense, localizing motor deficits. Infarction in penetrating branches from the posterior cerebral artery can involve the cerebral peduncle and adjacent oculomotor fascicles, creating the classic pattern of ipsilateral third nerve palsy with contralateral hemiparesis (Weber syndrome). The fixed superior perspective helps you teach why a unilateral peduncular injury, including compression in transtentorial (uncal) herniation, can distort descending pathways early and asymmetrically, long before lower brainstem signs dominate the exam. Neuroanatomy faculty can pair this illustration with axial MRI or CT at the midbrain level to reinforce how the basis pedunculi is positioned anterolaterally relative to the tegmentum and interpeduncular cistern. It also suits board-review figures, stroke pathway schematics, and operative anatomy discussions when introducing ventral midbrain surface landmarks for approaches around the interpeduncular region. Anatomical accuracy verified by SciePro's Medical Advisory Board.