Herpes simplex virus encephalitis involving the right thalamus.

Herpes simplex virus (HSV) encephalitis is a rare but often fatal disease if left untreated. A 50-year-old woman was admitted with lethargy, confusion, dysphasia and cough. MRI brain demonstrated bilateral temporal and perisylvian hyperintense signal abnormality extending into the cingulate gyrus, typical of HSV encephalitis. However, there was also signal abnormality involving the right thalamus, indicating thalamic involvement. EEG and cerebrospinal fluid PCR confirmed HSV encephalitis. The patient was started on intravenous acyclovir resulting in marked improvement. Adequate assessment and prompt treatment of HSV encephalitis will aid in achieving adequate recovery. Radiological investigation plays a crucial role in diagnosis with typical MR features a useful aid to diagnosis. HSV encephalitis classically involves the medial temporal lobes, insula and cingulated gyri. The basal ganglia and thalami are nearly always spared. We present a very rare case of HSV encephalitis which involved the right thalamus.