Transient global amnesia and hippocampal diffusion restriction: an overlooked radiological finding

Transient global amnesia (TGA) is characterized by isolated sudden anterograde amnesia. Diffusion restriction can be observed in the hippocampus on DWI-MRI at varying rates in TGA patients. This study analyzes the prevalence and characteristics of the hippocampal diffusion restriction (HDR), its relationship with vascular risk factors, and the prevalence of lesions overlooked in routine reports. 91 patients diagnosed with TGA at a tertiary hospital between 2011 and 2022 were evaluated retrospectively. The mean age was 64.8 ± 7.3 years, and 63.7% of patients were female. 75.8% of the patients had at least one vascular risk factor. Focal diffusion restriction was detected in 17 patients (18.5%) on DWI-MRI, with only one being extra-hippocampal. 81.2% of HDR was detected when DWI-MRI scan was performed between 12 and 96 h after the onset of symptoms. HDR was detected most when the imaging was performed in 24 to 48 h (p = 0.03). There was no correlation between the duration of symptoms and the detection rates of HDR (p = 0.55). In 9 patients (53% of 17) diffusion restriction was not specified in routine radiology reports. Although focal ischemia, venous flow abnormalities, migraine and epileptic phenomena have been suggested in its etiology, TGA is a clinical condition of which pathophysiology has not been determined clearly. Signal changes observed in DWI-MRI has led to discussions that cerebrovascular etiology may play a role, yet more comprehensive studies are required to prevent and manage TGA. HDRs can be overlooked in routine reports. Therefore, the DWI-MRI images of patients with TGA should be examined vigilantly.