Transient global amnesia (TGA) is an episodic dysfunction of declarative memory that usually resolves within less than 12 hours. Its cause is still poorly understood.
Studies on neuroimaging findings in TGA are heterogeneous and conflicting and most of them report the lack of obvious abnormalities.1 A recent study demonstrates a punctuate lesion on diffusion-weighted images (DWIs) in the hippocampus in more than 80% of patients with TGA.2 Can this hippocampal lesion be considered the structural correlate of TGA? Here we confirm the presence of this abnormality in 3 patients with TGA. The diagnosis of TGA was based on the current criteria.3 Within 5 months, 4 consecutive patients (aged 67, 65, 60, and 62 years) with TGA underwent brain magnetic resonance imaging (MRI). The MRI was performed within 4 days of the onset of symptoms: on day 3 in patient 1, on day 2 in patient 2, on day 4 in patient 3, and on day 2 in patient 4. In 3 of these patients, MRI (Figure 1) showed a small punctuate focus of high signal in the right hippocampus, clearly evident on DWI. The lesions matched with small areas of low signal on apparent diffusion coefficient maps. These signal abnormalities suggest ischemic lesions. The MRI showed no abnormalities in the remaining patient. Diffusion-weighted imaging allowed prompt recognition of small abnormalities in the hippocampus with high sensitivity; comparison and matching with correspondent apparent diffusion coefficient maps increased specificity.
Images from 3 patients with transient global amnesia showing axial fluid-attenuated inversion recovery (column A), diffusion-weighted images (DWIs) (column B), and apparent diffusion coefficient maps (column C) . On DWI a clear small punctuate focus of abnormal signal along the right hippocampal gyrus (column B, arrows) is visible in all of the patients. Hyperintensity in DWI corresponds to decreased diffusion, as seen in the apparent diffusion coefficient maps.
Follow-up magnetic resonance imaging scans 2 months after transient global amnesia in patient 1 showing axial fluid-attenuated inversion recovery images (A and C) and T2-weighted images (B and D) of the hippocampus at adjacent levels. There is no signal abnormality indicative of late ischemic changes.
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