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.
Transverse sinus
Promontory of middle car
Internal acoustic meatus
Mastoid antrum