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Abscesses of the nervous system
Cerebritis and cerebral abscess
A focal infection within the parenchyma of the brain – cerebritis – can lead to the formation of a cerebral abscess.
Often the causative organism cannot be identified, or a mixed growth of bacteria is found. Bacteria that cause cerebral abscesses include various Streptococci, Bacteroides, Staphylococci and Enterobacteria. Immuno-suppressed patients are predisposed to fungal abscesses such as Candida, Aspergillus and Toxoplasma.
The organism may enter the brain by direct extension from meningitis, otitis media or sinusitis, or by haematogenous spread, e.g. from infective endocarditis. Surgery or trauma may also inoculate organisms directly through an open wound. Multiple lesions suggest haematogenous seeding.
The onset of symptoms is usually insidious, with headache as the most common symptom, variable neck stiffness, fever, and possible focal signs, seizures or confusion.
In the first 1–2 weeks, there is inflammation and oedema (cerebritis). Later, necrosis and liquefaction lead to formation of a cavity filled with pus. There are acute inflammatory cells (neutrophils), surrounded by gliosis and fibroblasts.
Leucocytosis and a raised ESR are common.
· The diagnosis is made by CT or MRI scanning, but there may be non-specific oedema in the early stages. Later, ring-enhancement demonstrates the break-down in blood-brain barrier.
· In most cases lumbar puncture is contra-indicated due to risk of brain-stem herniation (coning), but aspiration or excision biopsy of the abscess may be carried out by a neurosurgeon if the organism is in doubt. Fungi and mycobacteria must be looked for.
Frequently treatment is by a combination of antimicrobial therapy and surgical drainage.
25% mortality despite treatment, epilepsy is common in survivors.
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