Characterization and evolution of diffusion MR imaging abnormalities in stroke patients undergoing intra-arterial thrombolysis

Abstract

Background and purpose: Lesions revealed by pretreatment diffusion-weighted imaging (DWI) may not progress to infarction, and apparent diffusion coefficient (ADC) or DWI thresholds for tissue viability may exist. We evaluated the evolution of abnormal DWI findings in patients with acute stroke who underwent thrombolysis.

Methods: Sixteen patients with acute occlusion of the anterior circulation underwent DWI followed by intra-arterial thrombolysis; follow-up CT or MR imaging was performed after reperfusion therapy. Lesion volumes were measured on all images. In three patients with abnormal DWI findings that appeared normal at follow-up, ADC values, ADC ratios, and DWI ratios were obtained on a section-by-section basis in the DWI-hyperintense regions that were either abnormal or normal at follow-up.

Results: In three patients, part of the DWI-hyperintense tissue appeared normal and part appeared abnormal at follow-up imaging. In one of these patients, the lesion decreased by -35.6%. In the other two, lesion growth appeared in regions that appeared normal at initial DWI: in one, the overall change in size was -2.4%, and in the other, the lesion increased by 89.8%. Respective mean changes at follow-up in normal-appearing and abnormal-appearing regions were: ADC, 731.7 x 10(-6) mm(2)/s and 650.4 x 10(-6) mm (2)/s; ADC ratio, 0.92 and 0.78; and DWI ratio, 1.16 and 1.32 (P <.001 for all measures).

Conclusion: In patients with acute stroke who undergo intra-arterial thrombolysis, most abnormal, pretreatment DWI findings indicate eventual infarction. In 19% of the patients described herein, DWI-hyperintense regions appeared normal at follow-up. ADC values, ADC ratios, and DWI ratios may be useful in identifying the portion of abnormal tissue that is potentially salvageable after reperfusion therapy.

Fig 1.

Images obtained in three patients in group B who had hyperintense regions at initial DWI that appeared normal at follow-up. Region 1 is DWI-hyperintense tissue that was abnormal at follow-up imaging. Region 2 is DWI-hyperintense tissue that was normal at follow-up imaging. A, ADC values in square millimeters per second. B, ADC ratios. C, DWI ratios.

Fig 2.

Reversal of DWI-hyperintense lesion after thrombolysis in a 68-year-old man with right-sided weakness and dysarthria. The patient had a left MCA occlusion that was successfully treated with IA tissue plasminogen activator at 6 hours. Initial DWI (row 1) and ADC (row 2) images demonstrate abnormality involving the left basal ganglia, insula, and subinsular region (short arrows) and in the left corona radiata (long arrow). At 3 days, follow-up (F/U) T2-weighted images demonstrate no abnormality in the left corona radiata. Lesions in the basal ganglia, insula, and subinsular region are unchanged. At discharge, the right-sided weakness had resolved.