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BACKGROUND AND PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Fifty patients presenting clinically with TIAs were examined angiographically. Twenty one patients (42%) had no abnormality. Twenty patients (40%) had stenosis or occlusion in the MCA, ACA or intracranial carotid, whereas 11 (22%) had involvement of their extracranial internal carotid artery. Seven of the 28 CTs performed showed basal ganglia infarcts. This suggests that the cause for the TIA was an infarct in the vascular territory of a lenticulostriate artery.

The relationship between high density (HD) on computed tomographic (CT) scans (which indicates a collection of blood in the subarachnoid space) and cerebral vasospasm was studied in 177 patients with ruptured aneurysm. The development of cerebral vasospasm was confirmed at the high rate of 84.6% in 26 cases where HD was demonstrated on the CT scan within 4 days after subarachnoid hemorrhage (SAH). In 8 cases where HD was not found on the CT scan obtained within 4 days after SAH, no cerebral vasospasm was seen. However, no relationship was found between HD and the occurrence of cerebral vasospasm in cases in which CT was performed after the 5th day of disease. It is suggested that CT performed within 4 days after SAH may give important information for predicting cerebral vasospasm.