Bacterial Meningitis And Brai... Health Article

Brain Abscess

Advances in the diagnosis and treatment of brain abscess have led to significant improvements in morbidity and mortality; these include widespread availability of non-invasive imaging techniques, improvements in antimicrobial agents that adequately penetrate the blood–brain barrier, and advances in neurosurgical procedures.

Epidemiology and microbiology: brain abscess is the most common focal suppurative brain infection, though it is relatively uncommon. The aetiology varies according to age and the presence of underlying disease. Brain abscess may be secondary to a focal infection in an adjacent site (e.g. otitis media, sinusitis), may follow penetrating trauma, or may arise from haematogenous dissemination of infection. In some patients, there is no recognized source of infection.

Pathology and pathophysiology: brain abscess is a focal suppurative infection of the brain parenchyma. It begins as an area of cerebritis, which may lead to ischaemic changes. Subsequent abscess formation is associated with accumulation of pus and development of a well-vascularized capsule. The rate of progression from early cerebritis to capsule formation is determined by the aetiological agent, the presence of underlying disease or immunopathology, and antimicrobial therapy.

Clinical features of brain abscess are often nonspecific and dia-gnosis may be delayed. The primary features at presentation result from the effects of a space-occupying lesion and include headaches, nausea, vomiting, lethargy, stupor and seizures. Focal neurological deficits (particularly hemiparesis) are common, but vary according to the size and location of the abscess. Fever is not always present. The presence of papilloedema is a worrying sign that suggests intracranial hypertension requiring urgent neuro-imaging.

Diagnosis: there are no pathognomonic laboratory markers of brain abscess. Blood culture should be performed, but is often not diagnostic. Lumbar puncture should not be performed, because of the significant risk of brain stem herniation. Inflammatory markers such as WBC count, C-reactive protein and ESR may be raised. CT and MRI are essential for diagnosis and should be performed early ( Figures 1 and 2). Serial scans have been shown to enable monitoring of therapy and determine the need for surgical intervention. Early cerebritis appears as a hypodense lesion, and the development of a capsule is associated with the appearance of a ring-enhancing lesion.

Management: stereotactic needle aspiration to drain the abscess is usually performed under CT or MRI guidance, to provide dia-gnostic specimens for culture and enable optimization of antibiotic therapy.

Table 4 lists empirical antibiotic therapy for brain abscess depending on the aetiology. Multiple antibiotic therapy may be required, because brain abscess is often caused by more than one organism. Parenteral antibiotics are given for 4–6 weeks. Patients who present with raised intracranial pressure may require additional treatment such as mannitol, corticosteroids and hyper-ventilation, as in bacterial meningitis. Routine use of cortico-steroids in the absence of intracranial hypertension is not recommended, because microbial clearance may be impaired.

Complications and long-term prognosis: seizures are common (25–50% of patients). Focal neurological deficits and mental retardation are recognized complications.

Poor prognostic indicators include delayed diagnosis, rapidly progressing disease, coma, multiple lesions, intraventricular rupture and a fungal cause. Outcome is poorer in the newborn and the elderly. However, the overall mortality is now less than 30%.

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Further Reading

1 Cohen J., Powderly W.. Infectious diseases 2nd edn. 2003 Mosby St Louis
2 Feigin R.D., Cherry J., Demmler G.J., Kaplan S.. Textbook of pediatric infectious diseases 5th edn. 2004 Saunders Philadelphia
3 Thwaites G.E., Nguyen D.B., Nguyen H.D.. Dexamethasone for the treatment of tuberculous meningitis in adolescents and adults N Engl J Med 351 2004 1741 1751