A patient undergoing posterior fossa surgery develops nystagmus directed away from the side of the lesion with the fast phase toward the normal side. The Romberg test shows falling toward the same side as the lesion. Cerebellar function tests are normal. This presentation is most consistent with a lesion of:

• A Flocculus of the cerebellum
• B Posterior semicircular canal on the side of the lesion
• C Fastigial nucleus of the cerebellum
• D Vestibular nucleus on the side of the lesion ✓

Explanation

Destruction of the vestibular nucleus causes nystagmus with the fast phase directed away from the lesion (toward the normal side) — a finding opposite to an acute peripheral labyrinthine lesion where fast phase is also away from the diseased side but the mechanism differs. Falling toward the lesioned side on Romberg indicates a vestibular imbalance. Normal cerebellar coordination tests and no limb ataxia suggest the cerebellar pathways themselves are intact. Floccular lesions cause gaze-evoked nystagmus and inability to suppress the VOR, not this pattern.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.