CT findings of Japanese encephalitis

Although the incidence of Japanese encephalitis has decreased markedly in Japan, sporadic cases are still observed in the southern part of Japan, including the Kurume district. In this study, CT findings of eight patients with Japanese encephalitis were analyzed. In principle, CT scans were done at the acute stage, within 3 weeks of the onset, and at the convalescent stage, after from 1 month to 1 year. The results may be divided into three groups: 1) normal scans, 2) low-density lesions, and 3) ventricular abnormalities. 1) Normal scans (Case 1, 5): CT scans in Case 1, taken 6 days after the onset, showed no abnormalities. The serial CT findings in Case 5 also revealed no changes, though the patient had clinically severe encephalitis. 2) Low-density lesions (Case 3, 4, 7): In Case 3, a slight low-density area was observed in the bilateral thalami only at the acute stage. CT scans in Case 4, obtained 2 and 4 months after the onset, exhibited low-density areas in the bilateral thalami, the left basal ganglia, and the left substantia nigra. In Case 7, diffuse low-density areas in the white matter were found 3 months after the onset. 3) Ventricular abnormalities (Case 2, 6, 8): CT in Case 2 revealed a moderate dilatation of the ventricular system, which probably suggests normal-pressure hydrocephalus. In 2 other cases, a narrowing or dilatation of the lateral ventricle was observed. The CT findings regarding Japanese encephalitis were discussed in comparison with those of other viral encephalitides, particularly herpes simplex encephalitis. (author)