The value of MRI in transient ischemic attack/minor stroke following a negative CT for predicting subsequent stroke

Diffusion weighted magnetic resonance imaging's (MRI) role in predicting subsequent strokes beyond the validated Canadian TIA Score in in transient ischemic attack (TIA)/minor stroke patients with normal CT scans is unknown. In this study, we assessed the incidence of acute cerebral infarction on MRI in these patients, overall and stratified by the Canadian TIA Score levels and then we assessed subsequent stroke rates at 7, 30 and 90 days based on the presence of acute infarct on MRI.

This pre-planned substudy of the Canadian TIA risk score cohort was conducted across 13 Canadian emergency departments over an 11-year period. Eligible patients included adult TIA/minor stroke patients with negative CT scans who underwent MRI within 7 days.

Among 11,507 patients, 1048 with negative CT scans had early MRI, which revealed infarction in 330 (31.5%) patients. Acute infarction rates varied by Canadian TIA Score risk group: 130 (15.4%) in low-risk, 754 (30.4%) in medium-risk, and 162 (50.0%) in the high-risk group. At 90 days, the rates of stroke in patients with a positive MRI were 2 (10.0%), 168 (22.3%), and 40 (24.7%) in low-risk, medium-risk, and high-risk groups, respectively. In comparison, in patients with a negative MRI the rate was 1 (0.9%), 7 (1.3%), and 4 (4.9%).

Combining the Canadian TIA Risk Score with follow-up MRI improves stroke risk assessment. MRI enhance the accuracy of diagnosis TIA, especially when CT is negative. The risk score helps prioritize MRI, benefiting medium-risk patients most, while high-risk patients need prompt management regardless of MRI results. Low-risk patients benefit from MRI for determining further investigations.