Mastoid Effusion Is NOT a Reliable Sign of Sinus Infection
Mastoid effusion is not a sign of sinus infection—it is instead associated with middle ear pathology (acute otitis media) or venous congestion, not paranasal sinus disease. 1, 2
Understanding the Anatomic Relationships
The mastoid air cells are part of the temporal bone and communicate directly with the middle ear cavity, not with the paranasal sinuses. 1 When evaluating mastoid effusion, you must distinguish between several distinct clinical entities:
Primary Associations of Mastoid Effusion
Mastoid effusion most commonly accompanies acute otitis media (AOM), representing extension of middle ear infection into the mastoid air cells rather than sinus pathology. 1, 3 The key examination findings include:
- Bulging tympanic membrane (most reliable sign of AOM) 2
- Intense erythema of the tympanic membrane 2
- Limited or absent tympanic membrane mobility indicating middle ear effusion 2
- Ear pain, fever, and irritability in the clinical presentation 2
Alternative Causes of Mastoid Effusion
Mastoid effusion can result from venous congestion in cases of dural sinus thrombosis, where the fluid accumulation is secondary to impaired venous drainage rather than infection. 4, 5 In patients with acute cerebral venous thrombosis, moderate-to-severe mastoid fluid signal is associated with increased clot burden (OR = 8.281,95% CI: 2.758-24.866). 5
Mastoid effusion frequently occurs as an incidental finding in children without clinical infection—61% of children undergoing MRI for non-infectious reasons showed findings in paranasal sinuses or mastoid cells, with 25% having mastoid cell fluid. 6
Clinical Distinction from Sinusitis
When examining a patient with suspected sinus infection, the physical findings are entirely different from those suggesting mastoid pathology:
Sinusitis Presentation 1
- Purulent nasal discharge and postnasal drainage 1
- Facial or dental pain over affected sinuses 1
- Nasal congestion with mucosal erythema 1
- Tenderness overlying the sinuses (maxillary, frontal) 1
- Cough, frequently worse at night 1
Mastoiditis Presentation 2, 3
- Mastoid tenderness on palpation 2
- Postauricular swelling and erythema 2, 3
- Protrusion of the auricle 2
- Fever with ear-related symptoms 2, 3
Critical Pitfalls to Avoid
Do not confuse mastoid effusion with sinusitis based on imaging alone. 6 The term "mastoiditis" should be used with great caution in radiological reports, as mucosal swelling in mastoid cells is frequently an incidental finding. 6 Treatment initiation should be based on clinical symptoms, not radiological abnormalities alone. 6
Always examine the mastoid area when evaluating severe or persistent AOM, as mastoiditis can develop despite prior antibiotic treatment (33-81% of mastoiditis cases had received antibiotics previously). 2
Recognize that mastoid effusion in the context of otitis externa may represent occult middle ear fluid—79% of patients with acute otitis externa showed fluid in the middle ear, mastoid, or both on CT imaging. 7
Diagnostic Approach
When mastoid effusion is identified on imaging:
- Perform otoscopic examination to evaluate for tympanic membrane abnormalities suggesting AOM 2
- Palpate the mastoid area for tenderness and examine for postauricular swelling 2, 3
- Assess for nasal symptoms separately—purulent rhinorrhea and facial pain suggest concurrent sinusitis, not a causal relationship 1
- Consider venous thrombosis if mastoid effusion is present without infectious symptoms, particularly in posterior fossa involvement 4, 5