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Home › Body Atlas › Sense Organs › Mastoid Antrum
Sense Organ Head & Skull

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.

Anatomical Data

Structure & Supply

LocationMastoid part of the temporal bone, behind and above the middle ear, about 12-15 mm deep to the suprameatal (MacEwen) triangle in adults
Parts
  • Aditus ad antrum (opening to the epitympanum)
  • Tegmen (roof separating it from the middle cranial fossa)
  • Openings of the mastoid air cells
Nerve SupplyMeningeal branch of the mandibular nerve; Tympanic plexus branches
Blood SupplyStylomastoid artery; Petrosal branch of the middle meningeal artery
Biomechanics

Function & Actions

The central air cell connecting the middle ear with the mastoid air cells, helping buffer middle ear pressure. It is the surgical landmark entered first in mastoidectomy.

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.

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