Brain perfusion in acute encephalitis: relationship to prognosis studied using SPECT. Single photon emission computed tomography (SPECT) and cranial computed tomography were sequentially examined in 2 patients with acute encephalitis. Radiographic computed tomography revealed focal low-density areas within a few days of the onset of symptoms in both patients. In SPECT, 1 patient exhibited hyperperfusion in the corresponding area, while the other had a normal scan. The outcome of the former was poor, while the latter recovered fully. Abnormal brain perfusion, thus, coincided with a poor prognosis. SPECT may be used to promptly evaluate the focal change of acute encephalitis. 