When it comes to MRI scans following stroke, a new study bluntly states “Do it or lose it,” as diagnostic yield is significantly reduced if a scan is not conducted in a timely manner, according to results published in the March issue of Stroke.

“Delayed MRI after [transient ischemic attack (TIA)] or minor stroke reduces the diagnostic yield and results in missed understanding of the lesion pattern,” wrote François Moreau, MD, of Centre Hospitalier Universitaire de Sherbrooke, Quebec, Candada, and colleagues. “MRI of minor stroke and TIA patients should occur early after symptom onset, and delayed imaging should be interpreted with caution.”

Results were based on a study of 263 TIA or minor stroke patients with a National Institute of Health Stroke Scale score of three or less. Baseline MRI was completed within 24 hours of symptom onset and follow-up MRI was conducted at 90 days. Baseline and 90-day scans were assessed independently, and patterns of stroke lesions were compared between the two time points.

The presence of a stroke in any location was more common at baseline than at 90 days, with detection rates of 68 percent and 56 percent, respectively, according to the authors. Thirty percent of patients with a negative 90-day scan had a clearly identifiable stroke at baseline. One-third of patients had differing lesion patterns on the baseline scan compared with the delayed follow up, and 90 percent of these patients had more lesions on the baseline scan.

“When interpreted blinded to the baseline scan, the presumed relevant lesion on the 90-day MR scan was the correct lesion in only 53 percent of patients,” wrote Moreau and colleagues.

The authors explained that MRI, including diffusion-weighted imaging, is the preferred modality for assessing TIA or minor stroke and should be completed with 24 hours of symptom onset. Knowing the location and distribution of lesions has diagnostic value in relation to the stroke mechanism and diffusion-weighted MR has prognostic value as a strong predictor of recurrent stroke, they noted.

Moreau and colleagues wrote that one limitation of the study is the development of new lesions between the first and second scan, which occurred in 10 percent of patients. “These new lesions had the opposite effect of increasing diagnostic yield of the delayed scan and represent a failure of poststroke secondary preventive therapy.”

They concluded that the results of the study support current guidelines and call for resources to be devoted to providing access to early MRI for patients with suspected TIA or minor stroke. “This study also suggests that late MRI must be interpreted with caution because the absence of abnormality does not guarantee the absence of pathology,” they added.

For more about stroke imaging, please read "Extending the Golden Window in Stroke Care," in Health Imaging.