During tympanomastoid surgery for attico-antral CSOM, the surgeon identifies a 'danger area' at risk of facial nerve injury in the mastoid. Which of the following best describes this area?

• A The horizontal (tympanic) segment of the facial nerve running below the lateral semicircular canal anterior to the oval window ✓
• B The vertical (mastoid) segment of the facial nerve as it descends posterior to the stylomastoid foramen between the digastric ridge anteriorly and the lateral semicircular canal posteriorly
• C The labyrinthine segment of the facial nerve passing through the petrous bone above the cochlea
• D The geniculate ganglion located at the anterior genu of the facial nerve

Explanation

The tympanic (horizontal) segment of the facial nerve runs in the medial wall of the middle ear, above the oval window and below the lateral semicircular canal. It is the most commonly injured segment during middle ear surgery because it is dehiscent (lacks a bony canal) in 55% of individuals. During mastoid surgery, the descending (vertical) segment runs posteromedial to the digastric ridge, but the tympanic segment is the most surgically vulnerable in middle ear dissection near the ossicles and oval window.

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.