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Neurology

Brain abscess

A brain abscess is a focal intracranial collection of infected material that combines a deep infection with an expanding mass, requiring urgent neurosurgical, infectious-disease and source-control management.

In a nutshell

Brain abscess is an intracranial emergency: suspect it with progressive headache, focal deficits, seizures or reduced consciousness, especially with an ENT, dental, cardiac, pulmonary, traumatic or postoperative source. MRI with DWI/ADC is preferred; urgent neurosurgical aspiration or excision plus prolonged specialist antimicrobials and source control are the core treatment.

Classic presentation

A patient with a chronic ear, sinus or dental source, or a right-to-left shunt, develops progressive headache, a focal deficit or first seizure. MRI shows a ring-enhancing lesion with central restricted diffusion.

Key points

  • Fever may be absent; treat the combination of a mass lesion and infection as an emergency.
  • MRI with DWI/ADC is preferred; ring enhancement alone is not diagnostic.
  • Do not perform lumbar puncture when there is mass effect or raised intracranial pressure.
  • Aspiration or excision provides decompression and material for culture whenever feasible.
  • Community-acquired empirical treatment uses a third-generation cephalosporin plus metronidazole under specialist direction; post-neurosurgical and immunocompromised cases need different cover.
  • Use corticosteroids for severe oedema symptoms or impending herniation, not routinely for every abscess.
  • Treat seizures when they occur; routine primary antiseizure prophylaxis is not recommended by ESCMID.
  • Complete prolonged specialist therapy, serial imaging, source control, rehabilitation and DVLA advice.

First-line investigation

Urgent MRI with contrast and DWI/ADC, or contrast CT if MRI is unavailable, with blood cultures, source assessment and neurosurgical sampling.

Management

Stabilise and escalate

  • Admit urgently, assess GCS and herniation risk, involve neurosurgery and microbiology, and do not perform lumbar puncture when a mass lesion is suspected.1,3

Image and obtain microbiology

  • Use MRI with DWI/ADC or contrast CT, take blood cultures, search for the source and obtain aspirate or excision material whenever feasible.3,1,2

Start source-appropriate antimicrobials

  • Community-acquired disease generally needs a third-generation cephalosporin plus metronidazole; post-neurosurgical and severely immunocompromised disease require a specialist alternative.3,5,6

Control oedema and seizures

  • Use corticosteroids for severe oedema symptoms or impending herniation and treat seizures when they occur; routine primary antiseizure prophylaxis is not recommended by ESCMID.3,6

Drain, control the source and tailor therapy

  • Drain or excise when feasible, treat the ENT, dental, cardiac, pulmonary or postoperative source, and narrow therapy to cultures, susceptibility and molecular results.3,4,5

Complete therapy and monitor recovery

  • Plan prolonged specialist antimicrobials, serial imaging, toxicity monitoring, seizure and rehabilitation follow-up, and DVLA advice.3,4,7

Exam traps

  • A ring-enhancing lesion is not automatically an abscess; diffusion restriction and the clinical context matter.
  • Do not perform lumbar puncture for a suspected space-occupying lesion.
  • Do not delay antibiotics in sepsis, impending herniation or other severe disease while waiting for aspiration.
  • Do not use one community-acquired antibiotic regimen for post-neurosurgical or severely immunocompromised disease.
  • Steroids are for significant oedema symptoms or herniation risk; antiepileptic prophylaxis is not routine without seizures.
  • A brain abscess has driving and seizure implications after discharge and needs explicit follow-up.

Illustrations

Ring-enhancing brain abscess on contrast MRIAxial post-contrast T1 MRI showing a small smooth ring-enhancing right parietal abscess with surrounding oedema. Label the modality and avoid implying that ring enhancement alone is diagnostic.Aimun AB Jamjoom, Abrar R Waliuddin and Abdulhakim B Jamjoom, Wikimedia Commons · CC-BY-2.5
Brain abscess on diffusion-weighted MRIMatched DWI, ADC and T1 MRI sequences showing restricted diffusion in the abscess cavity. Include a caption explaining that DWI is supportive and must be interpreted with the clinical and microbiological context.Harapan BN et al., Brain & Spine 2026, CC-BY-4.0 · CC-BY-4.0

Key sources

  1. NHS, Brain abscess (NHS condition information covering sources, symptoms, emergency status, CT/MRI, aspiration, treatment and complications; page last reviewed 18 October 2022)
  2. British Infection Association, UK cohort of brain-abscess microbiology (UK cohort describing microbial aetiology and the prominent role of Streptococcus intermedius; Journal of Infection 2020;80:623-629)Published 1 Jun 2020
  3. ESCMID guideline on diagnosis and treatment of brain abscess in children and adults (Clinical Microbiology and Infection 2024;30:66-89; current international specialist guideline used because no newer UK national brain-abscess guideline was identified)
  4. NHS, Brain abscess: treatment (NHS treatment information covering hospital care, medicine versus surgery, 2.5 cm as a broad public-information threshold, aspiration, craniotomy, follow-up imaging and recovery)
  5. NHS Greater Glasgow and Clyde Medicines, brain abscess pathway (Local NHS antimicrobial pathway for post-traumatic or bloodstream-source brain abscess; guideline reviewed October 2024 and page updated November 2024)Updated 1 Nov 2024
  6. BNF, current prescribing information for brain abscess treatment (Current UK prescribing source for CNS antimicrobials, antifungals, corticosteroids, antiseizure medicines and toxicity monitoring; direct access was restricted and the browser session was unavailable, so unsupported doses were omitted)
  7. GOV.UK, Brain abscess, cyst or encephalitis and driving (DVLA guidance requiring notification of a brain abscess, cyst or encephalitis)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.