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Findings: Region of edema and abnormal signal in the right insula and right temporal lobe. No evidence of abnormal enhancement is identified in this region of abnormality.
Diagnosis: Herpes encephalitis.
Discussion: Herpes encephalitis is typically caused by herpes simplex virus 2 in the neonatal population. Herpes simplex virus 1 is responsible for this entity in children and adults due to activation of a latent infection in the gasserian ganglion. This is the most common cause of a viral encephalitis.
Pathologically, this is a fulminant hemorrhagic necrotizing encephalitic process.
The neonatal form of this disease is typically a diffuse, nonfocal infectious process.
In the adult form, a predilection for the limbic system, particularly the temporal lobe, singulate gyrus, or subfrontal region is characteristic.
Imaging with CT or MRI may be performed with MRI being more sensitive than CT. Both of these examinations are typically normal with early disease onset. Although, on MR examination, early findings of edema as evidenced by decreased signal on T1 weighted imaging and increased signal on T2 weighted imaging may be found. The edema often extends into the insular cortex with sparing of the putamen. Post Gadolinium enhancement in this region is unusual in the early stages. In the late stage of disease, typically one to two weeks following onset of disease, the contralateral temporal lobe, insula, or singulate gyrus may become infected. Contrast enhancement and changes of subacute hemorrhages may be seen. The late sequelae of herpes simplex encephalitis includes encephalomalacia, atrophy, and dystrophic calcifications.
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