Transient Global Amnesia: A Diffusion and Perfusion MRI study

Transient global amnesia (TGA) is a rare clinical entity with a sudden onset of anterograde amnesia that recovers within 24 hours. The underlying pathophysiology is uncertain. Imaging studies are controversial, but diffusion-weighted images often show small diffusion-restricted lesions in the hippocampus, which may suggest ischemic damage. Thus, we conducted the first clinical study using neurite orientation dispersion and density imaging (NODDI) and arterial spin labeling (ASL) to examine whether the microstructure and perfusion status of the hippocampus are influenced by the presence of diffusion-restricted lesions.

Ten patients with a clinical diagnosis of TGA were evaluated by conventional MRI, NODDI, and ASL. The intracellular volume fraction (ICVF) and orientation dispersion index (ODI) on NODDI and cerebral blood flow (CBF) determined by ASL in the hippocampus were calculated and compared by diffusion-weighted imaging (DWI) positivity. Correlations among ICVF, ODI, and CBF were also analyzed.

Three patients had typical unilateral DWI-positive lesions. No significant differences in any of the three parameters were detected between DWI-positive and DWI-negative hippocampi. A statistically significant correlation was detected between the ODI and CBF (R = .51, P = .021).

The first NODDI and ASL study in patients after TGA demonstrated no obvious microstructural or perfusion abnormalities in the hippocampus with typical DWI-positive lesions, which may indicate that TGA does not cause destructive damage or involve baseline microstructure or perfusion abnormalities in the hippocampus in relation to diffusion-restricted lesions.