[Serial changes of SPECT and MRI findings in a patient with herpes simplex encephalitis].

We report a case of herpes simplex encephalitis in which the patient was repeatedly examined by magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT). The patient was a 36 year-old woman who had been transferred to our institution 6 days after the onset of symptoms with mild consciousness disturbance, nuchal rigidity, and high fever. Cerebrospinal fluid examination revealed an elevated mononuclear cell count with normal sugar concentration. Intravenous aciclovir was started 7 days after the onset of symptoms. The initial plain computed tomography (CT) scans did not reveal any abnormal findings, but contrast enhanced CT the next day showed a slight enhancement effect around the affected middle cerebral artery. Serial MRI showed the initial high intensity lesion starting on the medial cortex of the temporal lobe, then spreading to throughout the entire temporal lobe. During this period SPECT showed a marked, broad hot spot in the temporal lobe. The medial temporal lobe was high density on the CT 15 days after the onset. As the encephalitic lesion spread more laterally, the hot spot on SPECT moved laterally and then decreased in activity. Eleven weeks after the onset, the MRI showed intracerebral vacuolization of the lesion and it appeared as a wide cold spot on SPECT. The cause of the hot spot seen in the acute period was thought to be vasoparalysis of the affected area rather than breakdown of the blood-brain barrier, or impaired washout of the isotope, because the SPECT images after acetazolamide administration showed the cold spot even in the subacute phase.