During a cortical mastoidectomy for acute mastoiditis, the surgeon identifies the tegmen mastoideum superiorly and the sigmoid sinus posteriorly. The 'MacEwen's triangle' is used as a surface landmark to locate which structure?

• A Antrum (mastoid antrum) ✓
• B Sigmoid sinus
• C Facial nerve at second genu
• D Lateral semicircular canal

Explanation

MacEwen's triangle (suprameatal triangle) is a surface landmark posterior to the external auditory canal's posterosuperior wall. Its floor corresponds to the mastoid antrum, so drilling here provides the most direct route to the antrum in cortical mastoidectomy. The sigmoid sinus is posterior and deeper; the facial nerve second genu is medial to the lateral semicircular canal, identified only after entering the antrum.

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.