During a neurosurgical procedure in the posterior fossa, which nucleus in the floor of the 4th ventricle would be at risk of injury that could cause contralateral gaze palsy and ipsilateral facial palsy simultaneously?

• A Locus coeruleus
• B Hypoglossal trigone
• C Vestibular area
• D Facial colliculus (facial nerve fibers looping around abducens nucleus) ✓

Explanation

The facial colliculus is an elevation in the floor of the 4th ventricle formed by the facial nerve fibers as they loop around the abducens nucleus (CN VI nucleus). Damage to this area injures both the abducens nucleus (causing ipsilateral lateral gaze palsy — as the PPRF-abducens complex drives contralateral gaze) and the facial nerve fibers (causing ipsilateral LMN facial palsy). The hypoglossal trigone overlies the hypoglossal nucleus.

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

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Written and medically reviewed by the StethoPrep medical team.