Section Editor: Sandy Cheng-Yu Chen, M.D.
Taipei Medical University Hospital, Taipei, Taiwan
Herpes simplex virus (HSV) encephalitis is generally thought to occur as a form of reactivation of HSV-1 virus in the ganglion of the trigeminal nerve, which subsequently travels along a nerve axon to the brain. T2-weighted FLAIR MRI (figures A and B) reveals hyperintensity corresponding to edematous changes in the temporal lobes, inferior frontal lobes, and insula, with a predilection for the medial temporal lobes. The T2 hyperintensity reflects cytotoxic edema as shown with restricted diffusion on DWI (figure C). Typically, the basal ganglia are spared.