[Single photon emission CT in diagnosis of herpes simplex encephalitis--fronto-parietal hypo-accumulation associated...

Single photon emission CT (SPECT) using 123I-iodoamphetamine and magnetic resonance imaging (MRI) were performed in acute, subacute and chronic stages of a herpes simplex encephalitis (HSE). On the 5th day after onset, SPECT showed left temporal hyperaccumulation associated with decreased accumulation in ipsilateral posterior frontal and anterior parietal lobes. These altered accumulations were normalized on the 26th day, and a broad hypoaccumulation appeared in left temporal and surrounded area on the 91st day. The lesion in MRI was restricted to left temporal lobe and insula throughout the clinical course. Several authors reported temporal hyperaccumulation of lipophilic tracer in SPECT study of acute HSE, but its mechanism is controversial. Some postulate local hyperperfusion and others infer altered binding site of tracer. The fronto-parietal hypoaccumulation observed in our acute SPECT study suggests steal phenomenon in the territory of ipsilateral internal carotid artery, and supports temporal hyperperfusion as the origin of increased accumulation.