Mastoid Process: Anatomy, Air Cells, Surgical Landmarks, and Pathology

The mastoid process is a conical bony prominence of the temporal bone located posteroinferior to the external auditory meatus. It is a key surgical landmark and site of important pathology.

Anatomy

• Mastoid air cells: Pneumatized spaces lined with respiratory epithelium; variable number/size; communicate with middle ear via aditus ad antrum
• Mastoid antrum (antrum of Highmore): Largest air cell; present at birth; medial to suprameatal spine (Macewen's triangle)
• Mastoid cortex: Outer cortical bone; thickness variable (important for drilling)
• Sigmoid sinus: Posteromedial to mastoid air cells; risk during mastoidectomy
• Facial nerve: Descends in facial canal medial to air cells; second genu at pyramidal eminence
• Mastoid foramen: Transmits emissary vein to sigmoid sinus + meningeal branch of occipital artery

Surgical Landmarks (Cortical Mastoidectomy)

• Suprameatal spine (Henle's spine): Posterosuperior EAC; surface landmark for antrum
• Macewen's triangle (suprameatal triangle): Bounded by suprameatal spine, posterosuperior EAC, and tangential line from suprameatal spine → safe entry to antrum
• Korner's septum: Bony partition between antrum and mastoid air cells

Functions

• Pressure buffering for middle ear (gas exchange via mucosa)
• Protection of middle ear structures
• Attachment for sternocleidomastoid, posterior belly of digastric, longissimus capitis

Pathology

Condition	Key Features
Acute mastoiditis	Complication of AOM; postauricular pain, swelling, erythema, protruding pinna; CT: coalescent air cells
Chronic mastoiditis	Sclerosed/opacified cells; often with cholesteatoma
Cholesteatoma	Keratinizing squamous epithelium in middle ear/mastoid; bony erosion; recidivism
Mastoiditis complications	Sigmoid sinus thrombosis, Bezold's abscess (sternocleidomastoid), petrositis, meningitis, facial palsy
Langerhans cell histiocytosis	Lytic lesion in mastoid (eosinophilic granuloma)
Mastoid metastasis	Rare; from breast, lung, kidney, melanoma

Imaging

• CT temporal bone (fine-cut, axial/coronal): Gold standard for bony detail
• MRI: Soft tissue extension, dural enhancement, cholesteatoma (DWI hyperintensity)

Mastoid anatomy mastery is essential for otologic surgery and interpreting temporal bone imaging.