Herpes Simplex

            Herpes simplex is the commonest and gravest form of acute encephalitis with a 30-70% fatality rate and an equally high morbidity rate. It is almost always caused by Type 1 virus except in neonates where Type 2 predominates. Symptoms may reflect the propensity to involve the inferomedial frontal and temporal lobes- hallucinations, seizures, personality changes and aphasia. MR has demonstrated positive findings in viral encephalitis as soon as 2 days after symptoms, more quickly and definitively than CT. Early involvement of the limbic system and temporal lobes is characteristic of herpes simplex encephalitis. The cortical abnormalities are first noted as ill-defined areas of high signal on T2-weighted scans, usually beginning unilaterally but progressing to become bilateral. Edema, mass effect and gyral enhancement may also be present. Since MR is more sensitive than CT for detecting these early changes of encephalitis, hopefully it will improve the prognosis of this devastating disease.

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