Herpes Encephalitis

65-year-old male with fever and altered mental status. Numerous sites of abnormal T2/FLAIR-hyperintense foci within the subcortical white matter of the right and left frontoparietal regions. Signal abnormalities extend inferiorly to involve the insular/subinsular regions with extension into the mesial temporal lobes. There is involvement of the posterior aspects of the gyrus recti and orbitofrontal gyri on the ADC maps. There is no definite suspicious postcontrast enhancement. This is a case of herpes encephalitis. Herpes encephalitis is an infection most commonly caused by herpes simplex virus type 1. Imaging features usually include T2/FLAIR-hyperintensities within the limbic system. Lesions are usually associated with decreased diffusivity. The lesions are typically bilateral but asymmetric. The deep gray nuclei of the basal ganglia are usually spared. The differential diagnosis includes ischemia/infarct, status epilepticus, limbic encephalitis and infiltrating neoplasm.