Incidental Hippocampal Hyperintensity on Diffusion-weighted MRI: Individual Susceptibility to Transient Global Amnesia.

OBJECTIVES: Dot-like hippocampal hyperintensities (HHs) on diffusion-weighted MRI (DWI) have been reported as an interesting imaging finding of transient global amnesia (TGA) that is characterized by typical anterograde amnesia. However, we found that these dot-like HHs are occasionally seen in some patients without clinical symptoms of TGA.

METHODS: We identified 8 patients who did not show clinical symptoms of TGA, despite the presence of hippocampal lesions on DWI (No-TGA group, n=8). For the comparison group, 16 age-matched and sex-matched patients were selected from among patients who had been diagnosed with TGA (TGA group, n=16).

RESULTS: No significant difference was found in vascular risk factors, years of education, or underlying cognitive function between the 2 groups. More than half of the patients in each group performed preceding Valsalva-associated activities. Multiple hippocampal lesions or concomitant lesions in the cingulate gyrus were found only in the TGA group.

CONCLUSIONS: Dot-like HHs on DWI can be observed without the typical symptoms of TGA. Valsalva maneuver-associated activities could produce asymptomatic hippocampal lesions. The symptoms of TGA may be presented on a spectrum, from no symptoms to mild vegetative symptoms or to the typical symptoms of TGA, depending on individual susceptibility.