Focal Infections
Malignant External Otitis
Infection in external auditory canal; spreads to soft tissues to cause cellulitis and abscess.
Risk factors: diabetes in almost all patients; also advanced age, HIV infection.
Etiology: Pseudomonas aeruginosa, Aspergillus fumigatus.
Symptoms: facial nerve palsy (30%), otalgia, purulent otorrhea, hearing loss, painful swelling of surrounding tissues, mastoid tenderness.
Investigations: elevated ESR, sometimes mild leukocytosis; MRI findings; CT to detect bony erosion.
Treatment: ceftazidime or ciprofloxacin alone for small lesions; antipseudomonal penicillin plus aminoglycoside or third-generation cephalosporin for more extensive disease or drug resistance. Mortality 10–20% with treatment. Cranial nerve lesions imply poor prognosis.
Complications: osteomyelitis of skull base, abscess, meningitis, death.
Osteomyelitis of Skull Base
Rare complication of malignant external otitis, chronic mastoiditis, or paranasal sinus infection.
Etiology: P. aeruginosa most common.
Symptoms: headache, otalgia, hearing loss, otorrhea. Later, cranial nerve lesions. Fever frequently absent. Usually starts weeks or months after taking antibiotics for otitis.
Investigations: slight leukocytosis, high ESR, head CT.
Treatment: antipseudomonal penicillin or cephalosporin plus aminoglycoside. Mortality up to 40%. Poor prognostic factors: intracranial extension, cranial nerve involvement.
Brain Abscess
Encapsulated or free pus in brain parenchyma.
Incidence
Less than 2% of all intracranial surgery. Highest incidence before age 30 (25% before age 15).
Etiology
(1) Direct extension from cranial infection (mastoid, teeth, paranasal sinuses, osteomyelitis of skull). (2) Infections after skull fracture or neurosurgery. (3) Metastasis from infection in other organs (risk factors: congenital heart defects, pulmonary AVM, subacute infective endocarditis).
25–30% of brain abscesses have no obvious source.
Most common organisms: Staphylococcus aureus, streptococci, Enterobacteriaceae, Pseudomonas, anaerobes (e.g., Bacteroides). Gram-negative organisms most frequent in infants. Consider opportunistic organisms (e.g., Toxoplasma, fungi, Nocardia) in immunosuppressed patients.
Pathology
(1) Early cerebritis: patchy or nonenhancing hypodensity on imaging (days 1–3). (2) Late cerebritis: central necrosis, edema, ring enhancement on imaging (next 2 weeks). (c) Capsule formation.
Symptoms and Signs
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