Symmetrical external capsule lesions in a patient with herpes simplex encephalitis.

A 7-year-old boy had symmetrical transient high signal lesions in the external capsules on T2-weighted image during the recovery phase of herpes simplex virus (HSV) encephalitis. Although this finding has never been reported in HSV or other viral encephalitis, a postinfectious allergic mechanism is suspected in this patient. With the development of magnetic resonance imaging and other neuroimaging studies, a more detailed analysis of central nervous system is now possible.