Frenulum Of The Superior Medullary Velum Of The Brainstem (Rear View)

Description

Frenulum of the superior medullary velum occupies the midline of the dorsal brainstem at the rostral roof of the fourth ventricle. From this posterior perspective, the thin superior medullary velum spans between the paired superior cerebellar peduncles, while the frenulum forms a narrow longitudinal ridge where the membrane anchors and thickens. Just superior to this attachment, the dorsal midbrain surface leads toward the tectum (inferior colliculi region), and the trochlear nerves (CN IV) are positioned at the margin of the frenulum as they emerge on the posterior aspect of the brainstem. Trochlear nerve anatomy is easy to mislearn because CN IV is the only cranial nerve to exit dorsally and its fibers decussate before emergence, an arrangement that places surgical and traumatic vulnerability near the frenulum and superior medullary velum. Dorsal midbrain or superior cerebellar peduncle approaches, tectal plate lesions, and hemorrhage in the periaqueductal region can present with vertical diplopia from trochlear palsy, so a fixed posterior view that ties CN IV to the roof of the fourth ventricle clarifies topography better than abstract schematic diagrams. Midline relationships matter here. Small millimeters decide safe corridors. Neuroanatomy faculty commonly pair this illustration with lectures on the fourth ventricle roof (superior medullary velum, inferior medullary velum, tela choroidea) and with clinical teaching on dorsal brainstem syndromes and cranial nerve IV examination findings. It also fits operative anatomy chapters covering posterior fossa exposure, tumor corridors near the superior cerebellar peduncles, and lesion localization on the dorsal midbrain surface. Anatomical accuracy verified by SciePro's Medical Advisory Board.