Base Of The Peduncle Of The Brainstem, Lateral View

Description

Cerebral peduncle (crus cerebri) dominates the ventrolateral midbrain, with the basis pedunculi forming a thick, rounded column that continues inferiorly toward the pontine base and superiorly toward the diencephalon. From this lateral perspective, the peduncular base lies anterior to the midbrain tegmentum and medial to the lateral surface of the midbrain, defining the outer contour of the mesencephalon at the level where descending motor pathways concentrate. Medially, the region abuts the interpeduncular area where the oculomotor nerve (CN III) exits, while posterior to the basis pedunculi the plane transitions toward the substantia nigra and tegmental structures. Big motor highways. Clinically, the basis pedunculi matters because it carries densely packed corticospinal, corticobulbar, and corticopontine fibers, so small lesions can produce outsized deficits, classically contralateral hemiparesis and lower facial weakness with ipsilateral third nerve palsy in ventromedial midbrain infarction (Weber syndrome). The fixed lateral view emphasizes the ventral contour of the peduncle and helps learners map “motor tract territory” to the external surface landmarks that correlate with vascular supply from paramedian perforators and proximal posterior cerebral artery branches. It is also a useful reference when correlating midbrain compression patterns with uncal herniation, where the adjacent oculomotor fascicles are vulnerable. Neuroanatomy and neuroscience courses can pair this illustration with tract diagrams to anchor corticospinal pathway discussions at the midbrain level, and neurology or neurosurgery texts can place it alongside brainstem stroke syndromes for quick anatomic localization. It also supports radiology teaching when matching external midbrain anatomy to axial MR slices through the cerebral peduncles and substantia nigra. Anatomical accuracy verified by SciePro's Medical Advisory Board.