Intracranial abscess

CEREBRAL ABSCESS (contd) Clinical effects

Symptoms and signs usually develop over 2-3 weeks and progress. Occasionally the onset is more gradual, but features may develop acutely in the immunocompromised patient. Clinical features arise from:

- Toxicity - pyrexia, malaise (although systemic signs often absent).

- Raised intracranial pressure - headache, vomiting —> deterioration of conscious level.

- Focal damage - hemiparesis, dysphasia, ataxia, nystagmus

- epilepsy - partial or generalised, occurring in over 30%

- Infection source - tenderness over mastoid or sinuses, discharging ear.

bacterial endocarditis - cardiac murmurs, petechiae, splenomegaly.

- Neck stiffness due to coexistent meningitis or tonsillar herniation occurs in 25%.

n.b. Beware attributing patient's deteriorating clinical state to the primary condition, e.g. otitis media, thus delaying essential investigations.

Investigations

X-ray of the sinuses and mastoids: opacities indicate infection.

CT scan: in the stage of 'cerebritis' the CT scan may appear normal or only show an area of low density. As the abscess progresses, a characteristic appearance emerges:

Ventricular compression and midline shift due to mass effect

scan with i.v. contrast

Marked 'ring' enhancement - usually spherical

Central area of low density

Surrounding area of low density = oedema scan with i.v. contrast

Marked 'ring' enhancement - usually spherical

Central area of low density

Surrounding area of low density = oedema n.b. Always administer i.v. contrast to patients with suspected intracranial infection to avoid overlooking small abscesses.

CT scan may also reveal opacification of the mastoids or sinuses.

If abscesses occur at multiple sites, suspect a haematogenous source.

MRI: will more readily detect the 'cerebritic' stage, but does not distinguish infection from other pathologies.

Lumbar puncture is contraindicated in the presence of a suspected mass lesion, but if CSF is obtained inadvertantly, this will show f protein e.g. 1 g/1, ] white cell count (several hundred /ml) - polymorphs or lymphocytes. The Gram stain is occasionally positive. Peripheral blood - may show f ESR, leucocytosis. Blood culture is positive in 10%.

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