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Bone Head & Skull

Mastoid Air Cells

cellulae mastoideae

The mastoid air cells are a system of air-filled cavities within the mastoid process of the temporal bone, communicating with the middle ear through the aditus ad antrum and the mastoid antrum. The degree of pneumatisation varies widely, well-pneumatised mastoids are associated with good middle ear aeration; sclerotic mastoids result from chronic otitis media or developmental failure. The sigmoid sinus and facial nerve canal are important structures bordering the mastoid air cell system.

Anatomical Data

Structure & Landmarks

Articulations
  • Middle ear via mastoid antrum and aditus
  • Digastric groove: medially; sigmoid sinus: posteriorly
Landmarks
  • Mastoid process posterior to external auditory meatus
  • Mastoid antrum: largest air cell (4-5 mm diameter) at the anteromedial tip
  • Sigmoid sinus: medial wall of posterior air cells
  • Facial nerve canal passes through the air cell system laterally
OssificationPneumatisation of the mastoid begins after birth from the mastoid antrum and continues through childhood; its extent varies and is reduced by chronic middle ear disease in childhood.
Clinical Relevance

Clinical Notes

Mastoiditis (infection of the mastoid air cells) is a complication of otitis media, presenting with post-auricular erythema, oedema, and displacement of the auricle. Cortical mastoidectomy (removing the lateral air cells) and modified radical mastoidectomy (exteriorising the air cell system) treat mastoiditis. Cholesteatoma (keratinising squamous epithelium in the middle ear) invades the mastoid air cells and requires surgical eradication. CT of the temporal bone maps air cell anatomy, sinus position, and facial nerve canal proximity before mastoid surgery.

Pathology

Common Injuries & Conditions

Acute Mastoiditis Complicating Otitis Media

Bacterial otitis media spreads into the mastoid air cells producing acute mastoiditis with coalescence of air cells, post-auricular abscess, and risk of intracranial spread; CT confirms air cell coalescence and the absence of intracranial extension, and cortical mastoidectomy with wide antrostomy drains the mastoid infection and prevents complications.

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