Mesiotemporal T2-weighted hyperintensity: neurosyphilis mimicking herpes encephalitis

Abstract

Bilateral mesiotemporal hyperintensity on T2-weighted and fluid-attenuated inversion recovery MR images of a patient with a clinical syndrome of encephalitis is considered to be a classic finding for herpes simplex virus infection. We report a case of neurosyphilis with identical MR imaging abnormalities and a similar clinical presentation. Because syphilis is not routinely tested for, awareness of this mimicry of herpes simplex virus encephalitis is important, considering the potential therapeutic implications.

fig 1.

Images of a 50-year-old man with a 3-month history of progressive dementia, who presented with seizures. Serologic evidence of active neurosyphilis was present, and there was no evidence of herpes virus infection. A, Axial FLAIR image obtained at midbrain level. B, Axial FLAIR image obtained at the level of the pons. Asymmetrical bilateral signal hyperintensity in the mesial temporal lobes can be seen and is greater on the right side than on the left. C, Axial T1-weighted image obtained at the level of the low midbrain. This image shows mild left temporal lobe atrophy, evidenced by dilation of the temporal horn (arrow).

fig 2.

Axial FLAIR image of the same patient, obtained 10 days after treatment with penicillin. There are essentially no imaging differences as compared with the pretreatment images. fig 3. Axial FLAIR image of the same patient, obtained 4 months after treatment with penicillin. There is significant interval improvement in the previously noted mesial temporal signal abnormalities. There is also slight right temporal atrophy, with compensatory dilation of the temporal horn