A patient undergoes surgery for acoustic neuroma (vestibular schwannoma) via the retrosigmoid approach. Post-operatively, there is normal lacrimation and stapedial reflex, but the patient cannot close the eye and has loss of taste on the anterior two-thirds of the tongue. At which anatomical segment of the facial nerve was the surgical injury most likely?

• A Mastoid segment between the second genu and the stylomastoid foramen, above the chorda tympani origin ✓
• B Meatal segment (within the internal acoustic canal)
• C Labyrinthine segment (between the IAC and the geniculate ganglion)
• D Tympanic segment (between geniculate ganglion and second genu)

Explanation

The greater petrosal nerve (lacrimation) arises at the geniculate ganglion (labyrinthine-tympanic junction); the nerve to stapedius arises in the tympanic/proximal mastoid segment. Chorda tympani (taste anterior 2/3 tongue, submandibular/sublingual secretion) arises from the mastoid segment approximately 5–6 mm above the stylomastoid foramen. An injury below the nerve to stapedius but above the chorda tympani origin would spare lacrimation and stapedial reflex while causing facial palsy AND loss of taste — indicating the lesion is in the mastoid segment proximal to (above) the chorda tympani origin.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.