Diffusion-weighted imaging in transient global amnesia exposes the CA1 region of the hippocampus.
BACKGROUND
Transient global amnesia (TGA) is characterized by a sudden onset of anterograde amnesia without alteration of consciousness or personal identity. Interestingly, recent studies have reported a high frequency of small high-signal abnormalities in the hippocampus with diffusion-weighted (DW) imaging, and ischemia has been proposed as an etiology of TGA. We hypothesized that TGA lesions occur preferentially in the CA1 region of the hippocampus, known to be susceptible to ischemia.


METHODS
Over a 30-month period 34 patients with TGA underwent MRI including DW imaging within 4 days of symptom onset. Patients with high-signal abnormalities in the hippocampus on the initial DW images underwent subsequent DW and T2-weighted imaging in the coronal plane to identify the precise lesion locations.


RESULTS
Fourteen patients had small (1-3 mm) high-signal abnormalities in the hippocampus unilaterally on DW images. One of these patients had two lesions in one hippocampus and therefore in total 15 lesions were identified: four in the hippocampal head, and 11 in the body. Eleven lesions in ten patients with available coronal images were clearly demonstrated on both coronal DW and T2-weighted images and were localized to the lateral portion of the hippocampus, corresponding to the CA1 region.


CONCLUSIONS
Lesions associated with TGA were localized exclusively to the lateral portion of the hippocampus corresponding to the CA1 region. This finding supports the ischemic etiology of TGA; however, the pathophysiological mechanism involved requires further study.
Lee
Ho Yun
HY
Department of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, 300 Gumi-Dong, Bundang-Gu, Seongnam-Si, South Korea.
Kim
Jae Hyoung
JH
Weon
Young-Cheol
YC
Lee
Jung Seok
JS
Kim
Sang Yun
SY
Youn
Sung Won
SW
Kim
Sung Hyun
SH
D000328:Adult; D000368:Aged; D020236:Amnesia, Transient Global / Q000209:etiology / Q000473:pathology*; D002545:Brain Ischemia / Q000150:complications; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D020547:Lateral Ventricles / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012307:Risk Factors