This 33 year-old female patient presented with agitation, confusion, mutism, and fever. This axial diffusion-weighted MR image shows high signal in the cortex of the temporal lobes and insula, much more marked on the right. The calculated apparent diffusion coefficient map (click image) confirms restricted cortical diffusion and shows increased diffusion in the underlying white matter.

Lumbar puncture was performed – herpes simplex virus DNA was not shown on polymerase chain reaction. A brain biopsy was performed and the histology was consistent with encephalitis. PCR was repeated on the biopsy specimen and was positive for HSV type I.

HSV encephalitis typically produces abnormal signal +/- enhancement in the limbic system and temporal lobes. It is usually bilateral but asymmetrical. The basal ganglia are usually spared. The differential diagnoses include limbic encephalitis (paraneoplastic), gliomatosis cerebri, and status epilepticus. HSV-1 causes 95% of all herpetic encephalitides. Mortality ranges from 50-70%, and treatment is with intravenous antivirals.

Reference: Osborn A, et al. Diagnostic Imaging: Brain. Amirsys 2004
Credit: Dr Laughlin Dawes