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Mastoid air cells

The mastoid air cells are a network of interconnected, air-filled cavities within the mastoid process of the temporal bone. They vary widely in size, number, and degree of pneumatization among individuals. These cells communicate with the middle ear cavity through the aditus ad antrum and the mastoid antrum, forming an aerated extension of the middle ear system.

Their mucosa-lined structure helps maintain middle ear pressure, reduces skull weight, and provides a limited resonatory effect for sound conduction. Because of their close relationship with the facial nerve, sigmoid sinus, and posterior cranial fossa, mastoid air cells are clinically critical in infectious, traumatic, and postoperative evaluations.

Synonyms

  • Mastoid air cell system

  • Mastoid antrum and cell tracts

  • Mastoid pneumatization

Location and Structure

  • Position: Posterior portion of the temporal bone, extending from the mastoid antrum through the mastoid process.

  • Composition: Numerous septated air cavities lined by respiratory mucosa.

  • Connectivity: Communicate directly with the middle ear cleft via the aditus ad antrum.

  • Variability: Pneumatization ranges from well-developed (large cells) to sclerotic (minimal air spaces).

  • Development: Begins in infancy, matures through adolescence, influenced by recurrent infections.

Relations

  • Anteriorly: Middle ear cavity and epitympanum

  • Posteriorly: Sigmoid sinus and posterior cranial fossa

  • Superiorly: Middle cranial fossa dura

  • Inferiorly: Mastoid tip and digastric groove

  • Medially: Labyrinth and facial nerve canal

  • Laterally: External cortical bone of mastoid process

Function

  • Helps regulate air pressure within the middle ear

  • Contributes to sound conduction and resonance

  • Reduces weight of the cranial base

  • Provides insulation for delicate neurovascular structures adjacent to the temporal bone

Clinical Significance

  • Mastoiditis: Infection fills air cells with fluid or pus; may erode bone

  • Cholesteatoma extension: Soft-tissue mass may infiltrate or destroy mastoid septa

  • Temporal bone fractures: Longitudinal fractures often traverse mastoid cells

  • Postoperative cavities: After mastoidectomy, air cells may be obliterated or filled with scar

  • Otitis media complications: Impaired aeration due to blocked aditus causes effusion or chronic infections

  • Imaging relevance: CT is essential for mastoid anatomy; MRI evaluates soft tissue and intracranial complication

MRI Appearance

T1-weighted images:

  • Normal mastoid air cells: Very low signal (black), same as air in middle ear

  • Cortical bone: Low signal

  • Mucosal thickening or fluid:

    • Fluid appears intermediate to low signal

    • Proteinaceous or hemorrhagic fluid may be intermediate-to-bright

  • Cholesteatoma: Low-to-intermediate signal mass replacing air

  • Postoperative cavity: Intermediate soft-tissue signal replacing pneumatised cells

T2-weighted images:

  • Normal mastoid air spaces: Dark (signal void)

  • Mucosal thickening: Intermediate-to-bright signal

  • Fluid or infection: Bright hyperintense signal

  • Cholesteatoma: Hyperintense or intermediate depending on keratin content

  • Bone septa: Low-signal thin partitions

3D High-Resolution MRI (3D T2 or 3D CISS/SPACE variants):

  • Air: Signal void

  • Bony septa: Sharp low-signal lines

  • Soft-tissue filling (infection, cholesteatoma): Bright or intermediate

  • Excellent for:

    • Cholesteatoma evaluation

    • Detailed mapping of mastoid cavities

    • Postoperative surveillance

T1 Fat-Sat Post-Contrast:

  • Normal mastoid air cells: No enhancement (air contains no signal)

  • Inflamed mucosa: Smooth thin lining enhancement

  • Mastoiditis: Enhancing mucosa with non-enhancing internal fluid

  • Cholesteatoma: Typically does not enhance, but surrounding granulation tissue does

  • Abscess or osteomyelitis: Rim or diffuse enhancement with bone marrow changes

CT Temporal Bone Appearance

Non-Contrast CT (HRCT temporal bone):

  • Gold standard for evaluating mastoid anatomy

  • Normal mastoid cells: Black (air density) with thin bony septa

  • Well-pneumatized mastoid: Numerous large air cells

  • Sclerotic mastoid: Dense bone replacing air spaces

  • Common findings:

    • Mastoiditis: Soft-tissue opacification replacing air

    • Cholesteatoma: Soft-tissue density with thinning/erosion of septa

    • Fractures: Linear lucencies crossing mastoid cells

    • Sigmoid sinus dehiscence: Thinning or absence of bony plate

    • Postoperative mastoidectomy: Open cavity replacing cell system

MRI image

Mastoid cells mri axial image

MRI image

Mastoid cells mri CORONAL IMAGE

X Ray image

Mastoid air cells X RAY anatomy image -img-00000-00000

CT image

Mastoid air cells CT