Pathophysiology
The tympanic cavity of the middle ear is in communication with the mastoid antrum via a small canal that runs through the petrous temporal bone. Mastoiditis typically occurs when suppurative infection extends from a middle ear affected by acute otitis media (AOM) to the mastoid air cells. The mastoid air cells are related superiorly to the middle cranial fossa and posteriorly to the posterior cranial fossa. This means that infection of the mastoid can, rarely, spread to cause intracranial infection.
Aetiology
Mastoiditis is more common in young children < 2 years of age, and in patients with immunocompromise. Pre-existence of cholesteatoma is also a risk factor for subsequent mastoiditis.
Because acute otitis media (AOM) is the antecedent disease, the most common aetiologic agent causing mastoiditis is Streptococcus pneumoniae. Other implicated organisms include: Staphylococcus aureus, Streptococcus pyogenes, Haemophilus influenzae, group A Streptococcus pyogenes (GAS), Moraxella catarrhalis, and Pseudomonas aeruginosa.
Clinical features
Patients may present with a history of acute or recurrent otitis media. Persistent otorrhoea beyond 3 weeks is the most consistent sign that a process involving the mastoid has evolved. The patient's fever may be high and unrelenting in acute mastoiditis, but this may be related to the associated AOM. Persistence of fever, particularly when the patient is receiving adequate and appropriate antimicrobial agents, is common in mastoiditis. Pain (otalgia) is localised deep in or behind the ear and is typically worse at night. Persistence of pain is a warning sign of mastoid disease. This may be difficult to evaluate in very young patients. Hearing loss is common with all processes that involve the middle ear cleft. For infants, be attentive to any nonspecific history consistent with infection, such as poor feeding, fever, irritability, or diarrhoea.
Signs on examination:
- Protrusion of the pinna, loss of postauricular sulcus
- Post-auricular swelling, erythema, mass or fluctuance
- Otoscopy demonstrates features of otitis media
- Posterior/superior canal swelling
- Bulging and/or erythematous tympanic membrane
- Air-fluid level behind the tympanic membrane
- Purulent discharge
- Pyrexia
Differential diagnosis
- Otitis media or externa
- Lymphadenopathy
- Periauricular cellulitis
- Perichondritis
- Mumps
- Tumour
- Trauma
- Parotid swelling
- Basal skull fracture
Management
Initial Management:
- Admit under ENT
- Baseline investigations
- FBC, U&E, CRP
- Blood cultures (if pyrexia)
- Ear swab (if discharge)
Medical management
- High dose broad spectrum intravenous antibiotics e.g. IV ceftriaxone and metronidazole
- Microbiology advice for antibiotic sensitivities/if deteriorating/ treatment duration /de-escalation from IV to PO therapy
- Consideration of topical antibiotic treatment e.g. ciprofloxacin ear drops
- Regular observations and review
Indications for imaging (contrast enhanced CT petrous bones and brain):
- Clinical findings suggesting extracranial complications
- Postauricular abscess, neck mass, CN deficits, retro-orbital pain, vertigo, nystagmus
- Clinical findings suggesting intracranial complications
- Persistent headache or pyrexia, meningeal signs, CN deficits, focal neurology, altered consciousness
- Severe illness or toxic appearance
- Failure to improve after 24 hours of IV antibiotics
Surgical management
- Surgical intervention should be considered if there is:
- Subperiosteal abscess
- Mastoid osteitis
- Intracranial extension
- Co-existing cholesteatoma
- Limited improvement after IV antibiotics
- Surgical options include:
- Myringotomy +/- tympanostomy tube insertion
- Cortical mastoidectomy (if subperiosteal abscess identified on CT)
Complications
- Hearing loss
- Osteomyelitis or bone erosion
- Subperiosteal abscess
- Cranial nerve palsy (especially V, VI, VII)
- Intracranial spread
- Extradural abscess, cerebral abscess, subdural empyema, meningitis
- Venous sinus thrombosis
- Petrositis causing Gradenigo's syndrome (VIth cranial nerve palsy + deep trigeminal facial pain + suppurative otitis media)