DWI in transient global amnesia and TIA: proposal for an ischaemic origin of TGA

Abstract

There are conflicting reports concerning signal intensity changes in transient global amnesia (TGA) using diffusion weighted imaging (DWI). We prospectively analysed DWI signal intensity changes in TIA and TGA patients, and compared the clinical characteristics and risk factors of both groups. Using DWI and conventional T1 and T2 weighted turbo spin echo sequences, 28 patients with acute TGA (13 men, mean age 61.5 years) and 74 TIA patients (47 men, mean age 62.4 years) were studied within 48 hours after symptom onset. Every patient underwent an intensive diagnostic investigation. In 10/28 (36%) of the TGA patients and 21/74 (28%) of the TIA patients, DWI signal intensity changes occurred. The time to DWI and the duration of symptoms were comparable in TIA and TGA patients. Overall, TIA patients showed an increased prevalence of vascular risk factors compared with TGA patients. In the TGA group, patients with abnormal DWI showed carotid atherosclerosis significantly more frequently. Based on our data, we suggest that the aetiology of TGA could be explained by an ischaemic event; due to arterial thrombembolic ischaemia in one subgroup, particularly in those patients with increased vascular risk factors, and due to venous ischaemia in another subgroup with valsalva-like activities before symptom onset.T he aetiology and pathogenesis of transient global amnesia (TGA) is still unclear. Several different causes such as transient ischaemic attack (TIA), seizure, migraine, and venous congestion with consecutive ischaemia of memory relevant structures have been discussed previously.1 Several investigators have used diffusion weighted imaging (DWI) to further examine the aetiology of TGA and reported controversial results.2-4 Delayed DWI abnormalities were reported in 100% of a TGA population.5 Interestingly, DWI abnormalities were also reported in 21267% of TIA. [6][7][8] As none of the recent studies evaluated patients with acute TIA and TGA using early DWI, we prospectively investigated the prevalence of DWI signal intensities and vascular risk factors in patients with acute TGA compared with those with TIA.

Optimal Diffusion-Weighted Imaging Protocol for Lesion Detection in Transient Global Amnesia

“…This result concurred with the study by Sedlaczek et al, 9 in which the lesion-detection rate was 6% within 8 hours of onset and increased up to 84% at 48 hours after onset. The pathogenesis of TGA is uncertain, and various etiologic hypotheses have been proposed, including thromboembolism, 9,10 cerebral venous congestion induced by Valsalva-like activities, [18][19][20] and vasoconstriction caused by hyperventilation. 21 Whatever its etiology, several authors have suggested that delayed neuronal injury in the hippocampus is the cause of the delayed appearance of the lesions on DWI.…”

“…6 Recent diffusion-weighted imaging (DWI) studies have indicated the presence of focal hyperintensities involving the hippocampus in TGA. [7][8][9][10][11] The lesions detected by DWI are small and punctate (1-3 mm) and located within the lateral portion of the hippocampus. 9,11,12 Since Strupp et al 13 first detected hyperintense lesions in the hippocampus in TGA by using DWI, the frequency of lesions detected on DWI has been reported in a range of 0%-84%.…”

“…9,11,12 Since Strupp et al 13 first detected hyperintense lesions in the hippocampus in TGA by using DWI, the frequency of lesions detected on DWI has been reported in a range of 0%-84%. 9,10,14,15 According to a recent study, this discrepancy in detection rates appears to be attributable to the different timing of imaging from the onset of symptoms. 9 In this previous study, a detection rate of only 6% by DWI was achieved within several hours of symptom onset, but this increased up to 84% at 48 hours post-symptom onset.…”

Transient global amnesia following a transoceanic flight

“…13 Some investigators have used diffusion-weighted imaging to examine the etiology of TGA, but the results have been controversial. 14 Several conditions have been reported to precipitate TGA: physical exertion, emotional stress, sexual intercourse, swimming in cold water, 1 coronary angiogra- 18 and reactivation of Epstein-Barr virus infection. 19 Transient global amnesia has been associated with ischemic events (acute infarction in the retrosplenium of the corpus callosum, 20 common carotid artery occlusion, 21 scleroderma, 22 meningioma, 23 antiphospholipid antibodies, 24 thalamic infarction, 25 dural arteriovenous fistula of the anterior cranial fossa, 26 and epileptic events meningioma), 27 and herpes simplex encephalitis.…”

High-Resolution Diffusion-Weighted Imaging Increases Lesion Detectability in Patients with Transient Global Amnesia

“…[12][13][14][15] The detection rate of TGA lesions on DWI has been reported as a wide range between 0%-84%. 6,7,10,16,17 These variable rates of lesion detection are attributable to different imaging parameters such as section thickness, b-value, and imaging timing from the onset of symptoms. High b-value (ie, 2000 -3000 seconds/mm 2 ), thin section thickness (ie, 3 mm), and imaging 48 -72 hours after the onset of symptoms increased lesion detectability of DWI.…”