Diagnostic difficulties in computed tomography of brain abscesses.

In a series of 26 patients with the final diagnosis of brain abscess, 24 initially presented with ring lesions on computed tomography (CT) and two with homogeneous areas of increased attenuation after intravenous contrast medium administration. Twelve had a finding, reported to be characteristic, with a center of low attenuation encircled by a smooth, thin contrast enhancing ring surrounded by marked edema. In 10 patients, the true nature of the lesion was not evident from the first CT examination. An atypical appearance with a thick walled irregular ring or areas with homogeneous increased attenuation indicated malignant tumor. Rapidly progressing changes of the CT appearance and/or supplementary clinical data permitted us to reach the exact diagnosis in most of these. Repeat studies were also valuable in the follow-up during and after conservative (antibiotic) or surgical treatment.