Herpes Simplex Encephalitis

HSV encephalitis

This 33 year-old female patient presented with agitation, confusion, mutism, and fever. This coronal T2-weighted MR image shows high signal in the temporal lobes including hippocampal formations and parahippogampal gyrae, insulae, and right inferior frontal gyrus. The right gyrus rectus and the columns of the fornices were also involved (not shown). There was no associated haemorrhage or enhancement. There was moderate mass-effect.

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