A 45-year-old man develops a unilateral lower motor neuron facial nerve palsy involving the forehead. Where is the lesion most likely located?

• A Internal capsule (upper motor neuron lesion causing contralateral central palsy)
• B Nucleus of facial nerve in the pons
• C Facial nerve trunk distal to the stylomastoid foramen or within the parotid gland ✓
• D Geniculate ganglion within the petrous temporal bone

Explanation

A complete LMN facial nerve palsy (with forehead involvement) indicates a lesion at or distal to the facial nerve trunk — either at the stylomastoid foramen or within the parotid substance (parotid tumors, parotidectomy). Lesions proximal to the stylomastoid foramen (within the petrous bone) will additionally affect taste (chorda tympani = submandibular/sublingual secretion, taste anterior 2/3 tongue) and stapedius reflex (hyperacusis), as these branches arise before the foramen. The geniculate ganglion lesion (Ramsay Hunt syndrome) also causes LMN palsy with herpetic vesicles in the ear canal. UMN lesions spare the forehead because of bilateral cortical representation.

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

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Written and medically reviewed by the StethoPrep medical team.