What is Coalescent Mastoiditis?
Coalescent mastoiditis is a severe complication of acute otitis media characterized by bacterial infection that causes destruction and dissolution of the bony septations between mastoid air cells, creating a single cavity filled with purulent material. 1, 2, 3
Pathophysiology and Definition
Coalescent mastoiditis represents progression beyond simple acute mastoiditis, where the infection erodes through the thin bony walls separating individual mastoid air cells. 3 This process creates coalescence—the merging of previously separate air cells into larger cavities due to bone destruction. 1, 4 The condition carries significant risk for serious complications including subperiosteal abscess formation, intracranial spread, meningitis, and brain abscess. 2, 5
Clinical Presentation
The typical patient presents with:
- Recent onset of purulent otitis media, often incompletely treated with antibiotics 3
- Fever, lethargy, and irritability 3
- Red, bulging tympanic membrane (usually intact initially) 3
- Mastoid tenderness, retroauricular swelling, and protrusion of the auricle—the key distinguishing features from uncomplicated acute otitis media 1
- The affected ear protrudes downward and outward 3
- Postauricular abscess may be present 3
Diagnostic Imaging Findings
High-resolution CT of the temporal bone with IV contrast is the definitive diagnostic modality, showing cloudiness and dissolution of air cell septations, bone erosion, and coalescence of previously separate air cells. 1, 6 The addition of IV contrast improves detection of inflammatory tissue and abscesses. 1, 6
Epidemiology and Risk Factors
Coalescent mastoiditis occurs in the majority (84%) of acute mastoiditis cases requiring surgical intervention. 4 Importantly, 33-81% of mastoiditis cases had received prior antibiotic treatment for acute otitis media, demonstrating that coalescent mastoiditis can develop despite appropriate initial therapy. 1, 6 This underscores the importance of clinical vigilance and not relying solely on antibiotic treatment history.
Clinical Significance and Complications
Coalescent mastoiditis is associated with high rates of complications:
- Intracranial complications occur in approximately 16-23% of cases, including meningitis, peridural abscess, brain abscess, and dural venous sinus thrombosis 4, 5
- Intratemporal complications include subperiosteal abscess 4
- Anaerobic organisms are present in 29.4% of patients with intracranial complications versus only 5.7% without complications, indicating the importance of anaerobic coverage 5
- Streptococcus pneumoniae remains the most common causative organism overall 5
Management Implications
All patients with coalescent mastoiditis require mastoidectomy, while noncoalescent mastoiditis can be managed conservatively with broad-spectrum IV antibiotics and myringotomy. 4 The presence of bony erosion and coalescence on imaging is the critical factor determining surgical necessity. 7 Initial therapy includes myringotomy for culture and drainage, followed by complete mastoidectomy for coalescent disease. 3
Common Pitfalls
- Failing to examine the mastoid area in cases of severe or persistent acute otitis media can miss the diagnosis 1
- Relying on culture results alone is problematic, as cultures may be negative in 33-53% of cases 1, 6
- Delaying imaging when clinical deterioration occurs or when patients fail to improve after 48 hours of IV antibiotics increases morbidity and mortality 1, 6
- Misclassifying cases with any bony erosion as "uncomplicated" leads to inadequate treatment—coalescence itself represents complicated disease requiring surgical intervention 7