A 28-year-old woman undergoing stapes surgery is found to have a bare facial nerve crossing the oval window niche without any bony cover. Which segment of the facial canal is classically involved in this congenital dehiscence?
- A Labyrinthine segment
- B Tympanic segment ✓
- C Mastoid segment
- D Intracanalicular segment
Correct answer: B. Tympanic segment
Explanation
The tympanic (horizontal) second segment of the facial nerve runs in a bony canal above the oval window and below the lateral semicircular canal, medial to the incus. It is the most commonly dehiscent portion of the fallopian canal, reported in up to half of temporal bones, exposing the nerve directly over the oval window niche during stapes surgery. The labyrinthine segment is narrowest rather than most dehiscent, and mastoid and intracanalicular segments rarely lack bony cover.
Reference: Cummings Otolaryngology: Head and Neck Surgery, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.