Computed tomographic findings in acute viral encephalitis in adults with emphasis on herpes simplex encephalitis

Nine patients with acute viral encephalitis were diagnosed by CT. Seven had herpes simplex and two had nonherpetic acute viral encephalitis. All patients with herpes simplex encephalitis initially were febrile. They developed confusion and seizures. Five had focal neurological deficit and two had papilledema. The CT scan showed an abnormality on the initial CT in 6 of 7 cases. In one case initial CT study was normal; however follow-up scan (performed 5 days later) showed a definite abnormality. CT showed the characteristic pattern of herpes simplex encephalitis in all cases. This is a temporal lobe hypodense lesion (unilateral, 5 cases; bilateral, 2 cases) with a small interspersed hyperdense region. The hyperdense component represents hemorrhage. Mass effect was seen in all cases. Two patients showed enhancement which was diffuse or patchy in one case and cisternal-gyral in the other; however enhancement was absent in 5 cases. One patient showed progression of the size of the hypodense lesion despite antiviral treatment. Follow-up CT showed hypodense lesion(s) in the temporal lobe region with enlargement of the temporal horns and contiguous basal cisterns in 4 cases. In 2 other cases of acute viral encephalitis the patients initially developed fever, confusion and seizures. CT showed basal ganglia calcification or hypodense lesions.