Brain Abscesses

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

A brain abscess is a focal collection of pus within the brain parenchyma due to infection, typically caused by bacterial or fungal organisms. It is a life threatening condition requiring urgent intervention.

Aetiology

Brain abscesses develop from direct infection, haematogenous spread, or following head trauma or surgery.

Common Causative Organisms:

  • Bacterial: strep spp., Staph aureus, anaerobes (e.g., Bacteroides, Fusobacterium).
  • Fungal: aspergillus, Candida (common in immunocompromised patients).
  • Protozoal: toxoplasma gondii (in HIV/AIDS patients).

Pathophysiology

  • Infection leads to localised inflammation, forming a walled-off collection of pus.
  • Associated oedema increases intracranial pressure (ICP), causing neurological symptoms.
  • Untreated, it may rupture into the ventricles, leading to ventriculitis and meningitis.

Risk factors

  • Untreated otitis media or sinusitis (spread via adjacent bone).
  • Dental infections.
  • Head trauma or neurosurgical procedures.
  • Immunosuppression (HIV, chemotherapy, diabetes).
  • Congenital heart disease (right to left shunts increasing the risk of haematogenous spread).

Signs and symptoms

The presentation depends on the location and size of the abscess.

Classic Triad:

  • Headache: persistent and progressive.
  • Fever: may be absent in chronic cases.
  • Focal neurological deficits: weakness, speech disturbance, ataxia.

Other Symptoms:

  • Seizures: due to cortical irritation.
  • Altered mental state: confusion, drowsiness, or coma.
  • Signs of raised ICP: nausea, vomiting, papilloedema.

Investigations

  • Urgent CT or MRI with contrast: shows a ring enhancing lesion with surrounding oedema.
  • Blood cultures: identify bacteraemia.
  • Full blood count (FBC): shows leukocytosis.
  • Inflammatory markers: raised CRP/ESR.
  • Serology: consider for Toxoplasma in HIV patients.
  • Lumbar puncture: contraindicated due to risk of herniation.

Management

1. Empirical Antibiotic Therapy (IV for 6–8 weeks) follow loca/national guideline:

  • Ceftriaxone + Metronidazole: covers Gram pos, Gram neg, and anaerobic organisms.
  • Vancomycin: if MRSA is suspected.
  • Antifungals: if fungal infection is suspected.

2. Neurosurgical Intervention:

  • Aspiration or drainage.
  • Surgical excision: considered if there is poor response to aspiration or large multiloculated abscesses.

3. Adjunctive Therapy:

  • Dexamethasone: reduces cerebral oedema if there is significant mass effect.
  • Anticonvulsants: used if seizures occur.
  • Management of raised ICP: elevate head, IV mannitol if needed.

4. Long-Term Follow-Up:

  • Repeat imaging after treatment to assess resolution.
  • Monitor for residual neurological deficits.
NeurologymypanotesBrain Abscesses