Suprameatal triangle externally represents:
Suprameatal triangle, also known as MacEwen's triangle, is seen in temporal bone of skull, in  norma lateralis view.
It is a small area/depression present posterior and superior to external acoustic meatus.
It forms the lateral wall of mastoid antrum.
It is of importance to surgeons performing cortical mastoidectomy.

Boundaries of Suprameatal triangle:

Superiorly: By supramastoid crest.
Anteriorly: By posterosuperior margin of EAM (external acoustic meatus).
Posteriorly: Vertical tangent to posterior margin of EAM (external acoustic meatus).  
Anteroinferiorly: By presence of suprameatal spine.

Key Concept: 
Suprameatal triangle, also known as MacEwen's triangle, is seen in temporal bone of skull, in norma lateralis view. It represents mastoid antrum.