During cortical mastoidectomy for safe ear disease, the surgeon uses the suprameatal triangle (MacEwen's triangle) as the surface guide to enter the mastoid antrum. This triangle is bounded by:

• A Temporal squama above, tympanic ring in front, and the sinodural angle behind
• B Zygomatic arch below, Henle's spine behind, and the digastric ridge medially
• C Temporal line above, posterior meatal wall in front, and a vertical tangent to the posterior meatal wall behind ✓
• D Spine of Henle above, chordal ridge below, and the incudal fossa medially

Explanation

MacEwen's triangle is defined by the temporal line (suprameatal crest) superiorly, the posterosuperior margin of the bony external auditory canal anteriorly, and a vertical line drawn tangential to the posterior canal wall. The mastoid antrum lies about 12 to 15 mm deep to its centre in adults, making it the key landmark for safe antrum access during cortical mastoidectomy.

Reference: Dhingra's Diseases of Ear, Nose and Throat, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.