MacEwen triangle

Last revised by Francis Deng on 14 Mar 2021

The MacEwen triangle (also called the suprameatal triangle or mastoid fossa) is a surgical landmark on the surface of the temporal bone just superior to the external auditory canal used to locate the level of the mastoid antrum.

Three lines form the triangle:

  • superior: inferior temporal line/supramastoid crest extending back from the posterior root of the zygomatic process of the squamous temporal bone
  • anteroinferior: tangent extending up from the posterosuperior border of the external acoustic meatus, including the suprameatal spine of Henle
  • posterior: vertical tangent extending up from the posterior border of the external auditory canal

It is named after Sir William MacEwen (1864-1924), Scottish surgeon.

The mastoid antrum lies 1-2 cm deep to the triangle in the adult and thus serves as a landmark when performing a cortical mastoidectomy.

The cortical bone is thin in this area and thus susceptible to subperiosteal abscess formation in cases of coalescent mastoiditis.

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Cases and figures

  • Figure 1: McEwen triangle
    Drag here to reorder.