Diffusion MRI in patients with transient ischemic attacks

Background and Purpose - Diffusion MRI has established value in patients with ischemic stroke but has not been systematically investigated in patients with transient ischemic attack (TIA). Methods - Clinical, conventional MRI, and diffusion MRI data were collected on 42 consecutive patients with symptoms of cerebral TIA. TIA imaging data were compared with those from a contemporaneous group of 23 completed stroke patients. Results - Twenty of the 42 TIA patients (48%) demonstrated neuroanatomically relevant focal abnormalities on diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) imaging. When present, DWI/ADC signal changes in TIA patients were less pronounced and smaller in volume than those in completed stroke patients. TIA symptom duration was significantly longer for DWI- positive than for DWI-negative patients, 7.3 versus 3.2 hours. Diffusion MRI information changed the suspected anatomic and vascular TIA localization and the suspected etiologic mechanism in over one third of patients with diffusion MRI abnormalities. Of the 20 TIA patients with identifiable lesions on diffusion MRI, 9 had follow-up imaging studies; of these, 4 did not show a relevant infarct on follow-up imaging. Conclusions - Diffusion MRI demonstrates ischemic abnormalities in nearly half of clinically defined TIA patients. The percentage of patients with a DWI lesion increases with increasing total symptom duration. In nearly half, the diffusion MRI changes may be fully reversible, while in the remainder the diffusion MRI findings herald the development of a parenchymal infarct despite transient clinical symptoms. Finally, diffusion imaging results have significant clinical utility, frequently changing the presumed localization and etiologic mechanism.