CT of central nervous system infections in immunocompromised patients.

The computed tomographic (CT) scan appearance of parenchymal central nervous system (CNS) infection in 12 immunosuppressed patients was unlike that of the usual bacterial abscess in immunologically intact hosts. The lesions were poorly circumscribed and of low density. Contrast enhancement was minimal and did not assume a "ring" configuration. These CT scan findings heralded a poor prognosis. Compared to the neuropathologic findings, the CT scan generally underestimated the extent of involvement. Three other compromised patients were better able to localize the infection. This successful defense was manifested on their CT scans as the more typical "ring" pattern of contrast enhancement. Patients with this CT scan appearance of their CNS infection had a better prognosis.