Synopsis
Recognise a parenchymal brain abscess, protect against pressure and seizure complications, obtain microbiological diagnosis without unsafe delay, and identify a contiguous, haematogenous, postoperative or immune-status-specific source.
- A brain abscess is an intraparenchymal infection progressing from cerebritis to a capsule; headache, fever and focal deficit need not all be present.
- MRI should include DWI/ADC and T1 imaging before and after gadolinium. Restricted diffusion supports pus but is not perfectly specific; tumour, haemorrhage and other lesions can mimic it.
- ESCMID recommends aspiration or excision as soon as feasible in most cases. In a stable patient, antimicrobials may be withheld only if neurosurgery can sample promptly, preferably within 24 hours.
Key red flags
Falling consciousness, new unequal pupil, posturing, abnormal breathing or worsening focal deficit suggests dangerous mass effect or herniation.
New focal seizure, status epilepticus or failure to recover fully after a seizure requires emergency assessment and imaging.
Fever, sepsis physiology or bacteraemia with headache, focal deficit or altered behaviour should prompt intracranial infection assessment.
Recent sinus, dental, middle-ear or mastoid infection can spread contiguously; endocarditis, pulmonary or systemic infection can seed haematogenously.
Recent neurosurgery, penetrating trauma or cranial hardware changes likely organisms and empirical treatment; do not use a community-acquired regimen by default.
HIV, transplantation, neutropenia or other immune compromise broadens the differential to toxoplasma, fungi, Nocardia, tuberculosis and non-infectious mimics.
Look for headache, focal weakness, aphasia, visual-field change, ataxia, seizure, behaviour change and reduced consciousness. Fever and meningism may be absent.
Repeated vomiting, declining GCS, pupil or gaze change, posturing and abnormal breathing indicate escalating mass effect; stabilise and escalate before detailed source work.
Recent craniotomy, penetrating injury, CSF leak or hardware changes microbiology and source control. Use the post-neurosurgical rather than community empirical pathway.
Reasoning priorities
Define lesion number, location, capsule, pus-like diffusion, oedema, ventricular rupture and alternative diagnoses.
Restricted diffusion within a ring-enhancing lesion supports abscess but is not pathognomonic. Interpret with enhancement, susceptibility, perfusion, host and tissue results; urgent action follows mass effect and clinical trajectory.
Worked reasoning
A febrile patient with headache develops a seizure and progressive unilateral weakness; CT shows a ring-enhancing lesion with oedema.
- Treat this as a focal intracranial infection and pressure emergency: stabilise airway, oxygenation and circulation, treat seizure, document GCS/pupils and call neurosurgery plus infection specialists.
- Obtain contrast MRI with DWI/ADC when safe, avoiding lumbar puncture. Take blood cultures promptly if this does not delay treatment.
- Because neurological deterioration is severe disease, start the locally approved empirical regimen immediately and arrange urgent aspiration or excision rather than waiting untreated for sampling.
- Send operative material for broad culture, histology and context-directed molecular, fungal or mycobacterial testing; narrow therapy when results return.
- Search for and control the source using dental/ENT, bloodstream, cardiac, pulmonary, traumatic, postoperative and immune-status clues, then follow clinical and imaging response.
A stable patient has a suspected abscess without sepsis, threatened herniation or neurological deterioration.