A 45-year-old woman undergoing parotidectomy develops inability to close her eye, loss of the corneal reflex, and deviation of the angle of the mouth to the opposite side. The nerve injury is MOST likely at which segment of the facial nerve?

• A At the geniculate ganglion within the facial canal
• B At the stylomastoid foramen before entering the parotid ✓
• C Within the parotid gland after it divides into temporofacial and cervicofacial divisions
• D In the internal auditory meatus proximal to the geniculate

Explanation

The main trunk of the facial nerve exits the skull at the stylomastoid foramen and then immediately enters the parotid gland where it splits. An injury at the stylomastoid foramen — or in the brief extracranial extraparotid segment just before entry — would interrupt ALL motor branches to the face (temporal, zygomatic, buccal, marginal mandibular, cervical), producing complete ipsilateral lower motor neuron facial palsy including inability to close the eye and drooping of the angle of the mouth. Lesions within the parotid after bifurcation would be more selective. Geniculate lesions would also impair taste and lacrimation (chorda tympani and greater petrosal nerve), which are not described here.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.