Learning Objective: By the end of this lesson, the student should be able to describe the anatomy, borders, and surgical importance of the mastoid fossa (MacEwen’s triangle) and explain its relevance in cortical mastoidectomy.
The mastoid fossa — also known as MacEwen’s triangle or suprameatal triangle — is a triangular depression on the external surface of the temporal bone. It serves as a key surface landmark in otologic surgery, providing a safe entry point for access to the mastoid antrum during a cortical mastoidectomy.
Borders
| Border | Anatomical Feature | Description |
|---|---|---|
| Superior | Supramastoid crest | Continuation of the upper border of the posterior root of the zygomatic process |
| Anterior | Suprameatal spine (Spine of Henle) | Bony projection at the posterosuperior aspect of the external acoustic meatus |
| Posterior | Imaginary vertical line | Drawn tangential to the midpoint of the posterior wall of the external auditory canal |
The mastoid fossa lies posterior and superior to the external acoustic meatus, forming a triangular surface depression.
Contents
- The mastoid fossa itself does not contain any major neurovascular structures.
- It overlies the mastoid antrum, the largest of the mastoid air cells.
- Because it marks a “safe area” for surgical entry, it is an essential landmark in cortical mastoidectomy.
Clinical Relevance
Cortical Mastoidectomy
- Indication: Treatment of acute or chronic mastoiditis, where infection spreads from the middle ear to the mastoid air cells.
- Surgical relevance:
- The mastoid fossa overlies the mastoid antrum, guiding safe drilling.
- Prevents injury to deeper critical structures such as the facial nerve, sigmoid sinus, and middle cranial fossa.
Clinical Pearl: The mastoid fossa provides a surface landmark for safe surgical access — avoiding vital neurovascular structures while reaching the mastoid antrum.
Key Points
- The mastoid fossa (MacEwen’s triangle) is located posterior-superior to the external acoustic meatus.
- It serves as a surgical landmark for the mastoid antrum.
- Borders: supramastoid crest, suprameatal spine, and a vertical line through the posterior ear canal wall.
- Clinical importance: Used as a safe entry site in cortical mastoidectomy for mastoiditis.
