Brain abscess diagnosis
Modern-day imaging techniques such as CT and MRI allow the prompt confirmation of the clinical diagnosis of brain abscess 1). CT is commonly used for diagnosing abscesses in adults, because of its general availability and high specificity after contrast enhancement; it is more useful in older children than in neonates, in whom high water content of the brain reduces the contrast between normal and injured tissue. Diffusion-weighted MRI and post-contrast MRI have been gaining increasing importance in the evaluation of brain infections and abscesses because of its high sensitivity and specificity 2) 3).
Specimens obtained during surgery or stereotactic computerized axial tomography (CT) guided aspiration should be sent for aerobic, anaerobic, mycobacterial and fungal culture and, when indicated, for protozoa.
Laboratory Studies
Routine laboratory studies are not helpful for the diagnosis of brain abscess. Leukocytosis may be absent; in some series about 40% of patients have a normal peripheral white blood cell count. Acute-phase reactants are moderately helpful but nonspecific.
C-reactive protein
The C-reactive protein level is elevated in almost all patients, but the sedimentation rate can be only moderately elevated and sometimes is normal.
Blood cultures
Samples for blood cultures should be obtained in all suspected cases; although the yield is low, a positive result can be extremely valuable.
Head computed tomography
Head computed tomography with contrast during stage 1 (early cerebritis) may show only edema—an area of hypodensity—which may or may not enhance with contrast. If done very early in the course of infection, a contrast-enhanced CT may be normal. During later stages, there is the development of a space-occupying lesion with a hypodense center and later a ring-enhancing rim, which is often surrounded by a large area of edema. Occasionally, ring enhancement can be seen with late cerebritis; delayed administration of contrast that fills in the central hypodensity is suggestive that the lesion is still in the cerebritis stage. Although contrast-enhanced CT scanning is considered sensitive for the detection of brain abscesses, it is not specific. Brain abscesses tend to have smooth thin-walled capsules, whereas tumors tend to have more irregular capsules. There are additional characteristics of brain tumors, but some overlap exists with brain abscesses. It is important to note that brain abscesses and brain tumors may have an identical appearance on the CT scan.