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Mastoid Antrum

antrum mastoideum

The mastoid antrum is the largest and most consistent mastoid air cell, communicating with the middle ear via the aditus ad antrum and with the peripheral mastoid air cells. It lies posterior and slightly superior to the middle ear, with the sigmoid sinus posteriorly, the posterior cranial fossa medially, and the facial nerve running anterior and inferior. The antrum is present from birth even before mastoid pneumatisation develops.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The mastoid antrum is the primary surgical landmark in mastoidectomy, entered by drilling through the cortex of the mastoid process to the air cell system. Acute mastoiditis is infection spreading from the middle ear through the aditus ad antrum into the antrum and mastoid cells, producing post-auricular swelling, tenderness, and forward auricular displacement — the classic mastoiditis presentation requiring cortical mastoidectomy and IV antibiotics. The antrum roof (tegmen mastoideum) and posterior wall (sigmoid sinus) define the superior and posterior limits of safe drilling.

Pathology

Common Injuries & Conditions

Acute Mastoiditis Spreading from Middle Ear via Aditus

Unresolved acute otitis media spreads through the aditus ad antrum into the mastoid antrum, producing post-auricular erythema, swelling, and protrusion of the auricle forward; CT demonstrates air cell coalescence and cortical breakthrough, and cortical mastoidectomy with myringotomy is required when antibiotics fail or subperiosteal abscess forms.