The investigations of choice for a brain abscess include:
- chest and skull x-ray - to identify pulmonary, sinus and mastoid infection
- blood culture
- CT scanning is the investigation of choice:
- it must precede any consideration of lumbar puncture
- it characteristically reveals a central necrotic area of reduced radiodensity with surrounding area of cerebral oedema
- iv contrast can be used to highlight the oedematous region, so demarcating the abscess
- a ring enhancing lesion on CT may be abscess or tumour; classically abscesses have a smoother outline
- ventricular compression and midline shift may be evident due to the mass effect of the abscess
- a subdural empyema forms a thin but extensive area of reduced radiodensity on the surface of the brain or along the falx
- an extradural empyema is more localised and lentiform
N.B. lumbar puncture must not be performed until raised intracranial pressure secondary to an abscess has been excluded because of the risk of coning.
- if the diagnosis is uncertain a diagnostic Burr hole & aspiration (under CT guidance) could be done (1)
- a CT or MRI can also be used to detect an infected source responsible for the abscess (e.g. paranasal sinusitis, ear infection) (2)
References:
- 1. Morgan R. Picture Quiz: Cerebral abscess. StudentBMJ 2003;11
- 2. Whitfield P. The Management of Intracranial Abscesses. ACNR 2005; 5(1)