Computed tomography of herpes simplex encephalitis.

On the initial computed tomographic (CT) scan in 10 of 13 patients with herpes simplex encephalitis (HSE), the most characteristic finding was a unilateral, low-density lesion in the medial temporal lobe and/or insular cortex. This lesion was seen in all patients as the disease progressed. When associated with hemorrhage and streaked contrast enhancement this lesion added specificity to the CT scan, but this situation occurred in only 3 patients. Early in the course of HSE, focal CT findings localized the temporal lobe of greatest involvement in 12 patients; 1 had a normal initial CT scan.