Herpes simplex encephalitis: diffusion MR imaging findings

We studied five patients with herpes simplex encephalitis type I with diffu sion-weighted MR imaging, as this sequence provides information regarding t issue integrity. Diffusion-weighted imaging was obtained using the echo-pla nar sequence. True diffusion images (i.e. b = 1000 s/mm(2) images), and the ADC (apparent diffusion coefficient) values were studied. In addition, dif fusion imaging of 12 normal cases, 46 patients with acute ischemia (cytotox ic edema), and 12 patients with vasogenic edema were studied for comparison . La patients with herpes encephalitis, two distinct types of diffusion ima ging findings (on b = 1000 s/mm(2) images, and ADC maps) were noted: lesion s similar to cytotoxic edema, and lesions similar to vasogenic edema. The p atients with the former type of lesions had fulminating disease, and were i n severe clinical condition. Those with the latter represented early cases, and they were in fairly good clinical condition with a good outcome by pro mpt therapy. Diffusion imaging appears to be a promising sequence to monito r the changes in the brain tissue in herpes encephalitis, and in other infe ctions as well with respect to restriction of movement (cytotoxic edema) or relatively high-motion (vasogenic edema) of water molecules, providing dat a on the severity of the disease. (C) 2001 Elsevier Science Ltd. All rights reserved.