Brain abscess

Introduction

o Brain abscess is a suppurative collection of microbes within the brain parenchyma.
o The lesions can be single or multi-focal.
o This condition has a higher prevalence in areas with high HIV rates.
o In developed countries brain abscesses make up a small percentage of space occupying intracranial lesion cases.
o Brain abscess can theoretically arise from any pathogenic micro-organism (bacteria, fungi or parasite).
o There are different risk factors for each infectious agent.
o Brain abscesses can be polymicrobial or can be cryptogenic (unknown cause).
o Entry of organisms into the brain can be through direct extension or haematogenous spread.
o Multiple abscesses and abscesses in the grey-white matter junction are more likely to be due to haematological spread.

Presentation

o Headache
o Fever
o Focal neurology

History

o Recent history of upper respiratory tract infection including otitis media?
o History of meningitis?
o Recent dental procedure or infection?
o Recent neurosurgical procedure?
o History of endocarditis?
o HIV status or immunocompromised?
o IV drug use
o Does the patient have diabetes mellitus?
o History of chronic granulomatous disease?
o Currently on haemodialysis?

Vital signs

o Assess for cushings triad – irregular respirations, bradycardia and systolic hypertension.

Examination findings

o Assess the patient’s airways, breathing and circulation.

Full neurological examination

• Cranial nerve palsy – Third or sixth palsy
• Variable focal neurology
• Papilloedema
o Positive kernig or brudzinski sign

Cardiovascular examination

• May be signs suggestive of endocarditis – murmur, poor dentition e.t.c.

Laboratory investigation

o Full blood count - leukocytosis
o Serum erythrocyte sedimentation rate - raised
o Serum C-reactive protein - raised
o Serum Prothrombin time (PT) and Partial thromboplastin time (PTT) - normal
o Blood culture – positive/negative
o Serum toxoplasma titre – positive/negative

Radiological investigations

o CT or MRI brain – one or more ring enhancing lesions
o CT chest, abdomen, and pelvis – this is to screen for malignancy and is negative

Special investigations

o Bone scan – this is to screen for malignancy and is negative
o Lumbar puncture – rarely performed, but used to test for a Toxoplasma abscess

Management

o The management for different organisms are very similar, however different anti-microbials will be used dependent on known sensitivities.
o Initially the patient’s airways, breathing and circulation should be stabilized.
o Initial empirical antibiotic therapy:
• IV vancomycin 15mg/kg every 12 hour AND IV metronidazole 500mg every 6 hours AND IV ceftriaxone 2g every 12 hours.
o Prophylactic anticonvulsant monotherapy (monitor interaction with antibiotics):
• Oral phenytoin 1g on first day, followed by 300-600mg o.d. in 3 divided doses
• Oral carbamazepine 200-400mg b.d.
o Corticosteroid is used in acutely decompensating patients.
• IV dexamethasone 10mg stat dose, followed by 4-6mg orally every 6 hours.
o Surgical decompression
• Relieves mass effect on the brain.
• Obtain sample for culture.
• Decreases the infectious burden.
• Risk of spreading infection to ventricular system.

Complications

Short term:

• Ventriculitis
• Hyponatraemia

Short/Long term:

• Seizures
• Hydrocephalus
• Death

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