Brain Abscess
A brain abscess is a life-threatening intracranial infection, defined as an encapsulated collection of pus within the brain parenchyma.
This updated UKMLA guide to brain abscess is based on ESCMID guidelines, which cover causes, risk factors, symptoms, complications, diagnosis, and management.
Causes and Risk Factors
| Cause category | Predisposing factors | Implicated organisms |
|---|---|---|
| Community-acquired |
|
Brain abscesses are often polymicrobial
Oral cavity bacteria are most commonly implicated (~59% of all cases)
|
| Post-surgical and head trauma |
|
|
Brain abscesses in immunocompromised patients are often caused by opportunistic pathogens like fungi, parasites, and Nocardia spp. [Ref]
Clinical Features
Symptoms are often nonspecific and depend largely on the size and location of the lesion. [Ref]
Classic triad for brain abscess: [Ref]
- Headache – most common symptom (seen in up to 70% of cases)
- Pain is usually localised to the site of the abscess
- It can be gradual or sudden onset, often severe and is typically not relieved by simple analgesia
- Fever (only present in 45-53% of cases)
- Fever may be absent, especially in chronic / subacute presentations
- Focal neurological deficit (depends on the abscess location), such as
- Limb weakness and/or sensory loss
- Dysphasia / aphasia
- Visual field defects
- Ataxia
- Cranial nerve palsy (esp. CN III, VI)
- Seizures
Other features: [Ref]
- Nausea and vomiting
- Changes in mental status
- Personality or behavioural change
Seizures can be the initial manifestation of a brain abscess. [Ref]
Location-Specific Clinical Features
Clinical presentation may vary depending on the affected brain region. This is a high-yield pattern recognition table:
| Abscess location | Key patterns / features |
|---|---|
| Frontal lobe |
|
| Temporal lobe |
|
| Parietal lobe |
|
| Occipital lobe |
|
| Cerebellum |
|
| Brainstem |
|
Complications
Key acute complications: [Ref1][Ref2]
- Abscess rupture → fulminant meningitis and/or ventriculitis
- Raised ICP and brain herniation (due to severe peri-focal oedema)
- Obstructive hydrocephalus
As a result, brain abscesses carry a significant mortality risk
Long-term complications are common, even after the infection is successfully cured: [Ref1][Ref2]
- Residual focal neurological deficits
- New-onset epilepsy
- Neurocognitive and psychosocial, psychiatric complications
Investigation and Diagnosis
Investigations overlap with the management, also see the management section for the algorithm overview.
Laboratory Tests
- Blood cultures – all patients
- Routine blood tests, including WBC count, CRP, procalcitonin (but they are NOT reliable in ruling in or ruling out a brain abscess)
- Consider HIV testing in all patients who present with a non-traumatic brain abscess
Diagnostic Work-Up
1st line investigation: neuroimaging
- Preferred modality: MRI brain
- If MRI is unavailable: CT head with contrast
Neuroimaging findings:
- A ring-enhancing lesion with surrounding oedema
- Brain abscesses can be singular or multiple
- Mass effect is possible if the abscess is large
MRI is more sensitive than CT in differentiating a brain abscess from other ring-enhancing lesions (e.g. tumour, metastasis)
If neuroimaging is suggestive of a brain abscess → neurosurgical intervention (gold standard)
- Methods:
- Preferred and most common: pus aspiration (stereotactic or image-guided)
- Open surgical excision
- Neurosurgical intervention is both diagnostic and therapeutic
- Diagnostic: extracted pus to be sent to culture and histopathological analysis to identify the organism and confirm diagnosis
- Therapeutic: drains the pus to achieve local source control
A lumbar puncture is relatively contraindicated in patients with suspected brain abscess due to the risk of brain herniation. Furthermore, it provides a very low diagnostic yield.
Identifying Primary Source
The following are only performed if clinically suspected or indicated:
- ENT and dental / maxillofacial consultation – if there is suspected ENT or oral infection / neurosurgical culture is +ve for oral cavity bacteria
- Systemic imaging (chest X-ray or CT TAP) – only if primary source of infection remains unclear after initial assessment
- TOE – only if infective endocarditis is suspected (e.g. monomicrobial abscess caused by Streptococcus or Staphylococcus with no other obvious cause)
- CTPA – only for those with recurrent brain abscess for unknown reasons to exclude PAVMs
Management
The management of brain abscess overlaps with certain investigations.
The standard management approach in order of priority, once a brain abscess is suspected:
| Step / priority | Description / purpose |
|---|---|
| 1. Urgent neuroimaging | To exclude other differential diagnoses and support the working diagnosis |
| 2. Neurosurgical involvement | If neuroimaging supports a brain abscess, discuss with neurosurgery urgently.
If neurosurgical intervention can be performed promptly (ideally within 24 hours):
If a significant delay (e.g. >24 hours) is expected before neurosurgical interventions can be performed:
Choice of antibioticsRefer to local guideline in practice. The recommended antibiotic choice from the ESCMID guidelines is included for reference. The choice depends on the following factors:
|
| 3. Targeted IV antibiotics | Adjust antibiotics once culture and sensitivity results are available. |
Do NOT delay antibiotics if a patient presents with severe disease (e.g. sepsis, impending brain herniation, imminent abscess rupture).
In these cases, start empirical IV antibiotics immediately after neuroimaging, then involve neurosurgery urgently.