During cortical mastoidectomy, the MacEwen's triangle is used as a surface landmark to locate the mastoid antrum. The three boundaries of MacEwen's triangle are:
- A Supramastoid crest (horizontal), tangent to posterior wall of EAC (vertical), and posterior boundary of the ear canal ✓
- B Superior temporal line, posterior wall of EAC, and anterior border of mastoid process
- C Posterior root of zygoma, supramastoid crest, and vertical line through posterior EAC
- D Tragal pointer, mastoid tip, and linea temporalis
Correct answer: A. Supramastoid crest (horizontal), tangent to posterior wall of EAC (vertical), and posterior boundary of the ear canal
Explanation
MacEwen's suprameatal triangle (also called the suprameatal fossa) is bounded by the supramastoid crest (linea temporalis) superiorly, a vertical line along the posterior wall of the external auditory canal anteriorly, and the posterior wall of the ear canal posteroinferiorly. The mastoid antrum lies approximately 15 mm deep to the center of this triangle in adults. This is the key surgical landmark for beginning mastoid antrum exploration in cortical mastoidectomy and avoiding the middle fossa dura superiorly.
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.