Herpes Encephalitis
(not all same patient)

Findings:
The MR images were obtained on an adult patient, showing asymmetric abnormal signal in both temporal lobes, extending to the insular cortex. The CT images are from a pediatric patient, showing extensive hemorrhagic necrotic changes throughout both cerebral hemispheres with sparing of the cerebellum. Intraventricular hemorrhage is present as well. The hemorrhagic process is centered in the temporal lobes.

Differential Diagnosis:
Signal abnormality involving both temporal lobes has a relatively limited differential diagnosis and is nearly pathognomonic for herpes encephalitis. Trauma with multifocal contusions and shear injury could be considered if there was appropriate history. Other less likely considerations include metastatic disease or multiple venous infarctions.

Discussion:
   -most common nonepidemic viral encephalitis
    neonatal:
           -birth canal transmission- HSV II, usually spontaneous Ab
           -attacks endothelium
           -2-4 wks-->seizures and severe hemorrhagic encephalitis (no preference for temporal lobes)
           -complications: mental retardation, ventmegaly, microcephaly/microphthalmia, multicystic encephalomalacia, Ca++
    adult, pediatric:
           -HSV I reactivation
           -prodrome: fever malaise 60%, URI 30%
           -seizures, confusion, encephalitis, focal deficits, cranial neuritis, 70% untreated mortality
           -EEG spike and slow wave
    imaging:
           -50% normal early CT +/- patchy WM/cortical hypo/hyperdensities sparing BG, thal, cerebellum
           -progression to necrosis +/- hemorrhagic, calcification, encephalomalacia
           -MR more sensitive for early changes- gray matter edema, possible meningeal enhancement
           -predilection for temporal lobes- latency in trigeminal ganglion, possibly more P-O involvement in children
           -look for cingulate gyrus, insular cortex involvement

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