Brain Abscess

A focal, encapsulated collection of pus within brain parenchyma, from contiguous spread (sinusitis, otitis media/mastoiditis, dental infection), hematogenous spread (endocarditis, particularly right-to-left cardiac shunts allowing bypass of pulmonary filtration, and bronchiectasis or lung abscess), direct inoculation (trauma, neurosurgery), or, in a significant minority, no identifiable source.

Often polymicrobial, particularly with a contiguous or dental source (streptococci, anaerobes).

Headache (the most common symptom, often progressive and poorly responsive to simple analgesia), fever (present in only about half), focal neurological deficit corresponding to the lesion location, and seizures.

Signs of raised intracranial pressure (papilledema, vomiting, declining consciousness) reflect mass effect and can evolve over days to weeks depending on abscess growth rate and location.

Contrast-enhanced MRI is the investigation of choice, with diffusion-weighted imaging particularly useful for distinguishing abscess (restricted diffusion within the cavity) from necrotic tumor.

Lumbar puncture is contraindicated given the mass effect and herniation risk.

Stereotactic or CT-guided aspiration provides microbiological diagnosis and, often, therapeutic decompression simultaneously.

Blood cultures and screening for the underlying source (sinus imaging, echocardiography if endocarditis or a cardiac shunt is suspected, dental assessment).

• Aspiration or excision, combined with prolonged antibiotics, is standard for most abscesses over roughly 2.5 cm; small (under 2.5 cm), non-mass-effect abscesses in a stable patient may occasionally be managed with antibiotics alone with close imaging follow-up
• Empirical antibiotics (before or pending culture): a combination such as ceftriaxone 2 g bd plus metronidazole, with vancomycin added where post-surgical, post-traumatic, or hematogenous S. aureus spread is a concern; regimen rationalized once organism identified
• Total antibiotic duration typically 6 to 8 weeks IV, sometimes longer with a subsequent oral course, guided by serial imaging showing resolution
• Corticosteroids (dexamethasone) are used for significant surrounding edema and mass effect, but only as an adjunct given a theoretical concern about reduced antibiotic penetration and capsule formation, not as a substitute for source control
• Anticonvulsants for seizures; treatment of the underlying source (sinus, ear, dental, cardiac) is essential alongside abscess management

Referral: neurosurgical emergency for aspiration/drainage; infectious disease for antibiotic duration; source-specific specialty (ENT, cardiology, dentistry) for the underlying cause.