Synopsis
Recognise a focal intracranial infection, avoid hazardous lumbar puncture, identify the likely source, and coordinate urgent imaging, neurosurgical microbiology and prolonged organism-directed therapy.
- Brain abscess evolves from focal cerebritis into a capsule containing pus; symptoms reflect location, oedema and raised intracranial pressure as much as systemic infection.
- Headache, focal deficit, seizure, cognitive change and fever are common components, but the classic triad of fever, headache and focal neurology is absent in many cases.
- Contiguous spread follows chronic otitis or mastoiditis, sinus or dental infection, while haematogenous spread can arise from endocarditis, lung infection, right-to-left cardiac shunt or injected drug use.
- Recent neurosurgery, penetrating trauma and cranial hardware introduce staphylococci and resistant healthcare-associated organisms; immunosuppression widens the differential to fungi and parasites.
- MRI with contrast and diffusion-weighted imaging best characterises a collection, surrounding cerebritis, multiplicity and ventricular extension; contrast CT is the rapid alternative when MRI is unavailable.
- Restricted diffusion supports pus but is not perfectly specific, and ring enhancement also occurs with metastasis, glioblastoma, toxoplasmosis, tuberculoma and treatment-related change.
- Do not use lumbar puncture to diagnose a suspected brain abscess because yield is poor and mass effect may make the procedure dangerous.
- Neurosurgical stereotactic aspiration provides source control, reduces pressure and yields bacterial, fungal and mycobacterial samples; excision is selected for particular anatomy, recurrence or foreign material.
- Community empirical therapy commonly includes a third-generation cephalosporin plus metronidazole, modified immediately for allergy, post-neurosurgical context, immune status and local resistance advice.
- Treatment usually lasts several weeks and is guided by drainage, organism, response and serial imaging; exact intravenous-to-oral decisions belong to a multidisciplinary infection and neurosurgical team.
Key red flags
Falling consciousness, unequal pupils, extensor posturing, bradycardia with hypertension or progressive vomiting indicates dangerous mass effect and needs immediate critical-care and neurosurgical action.
Investigation priorities
Define lesion number, site, capsule, pus characteristics, oedema and ventricular proximity.
Management branches
Progressive headache, seizure or focal deficit occurs with an infection source or immune risk.
- Stabilise airway and circulation, treat seizures and obtain urgent contrast CT or MRI while checking for raised-pressure signs and avoiding lumbar puncture.
- Contact neurosurgery and infection specialists as soon as imaging suggests abscess, arranging transfer to a centre able to drain and monitor intracranial complications.
- Take blood cultures and urgent laboratory samples, but start empirical intravenous treatment immediately if sepsis, neurological decline or procedural delay makes waiting unsafe.
Key medicines
CeftriaxoneUse the current local central-nervous-system infection dose intravenously, commonly 2 g twice daily in adults, with infection-specialist confirmation and renal or hepatic context.It does not cover anaerobes alone and may be inappropriate after neurosurgery; review severe beta-lactam allergy, biliary complications, cultures and local resistance.
MetronidazoleA common adult intravenous or oral regimen is 500 mg every 8 hours, but route and duration must follow the abscess protocol and microbiological findings.Prolonged exposure can cause peripheral or central neurotoxicity; review liver disease, alcohol advice, warfarin interaction and cumulative duration during neurological monitoring.