Chirantan Banerjee, MD
Kate MP, Riaz P, Gioia L, Sivakumar L, Jeerakathil T, Buck B, et al. Dynamic Evolution of Diffusion-Weighted Imaging Lesions in Patients With Minor Ischemic Stroke. Stroke. 2015
MRI revolutionized ischemic stroke care with its advent. Diffusion weighted imaging (DWI) was initially believed to represent infarct core. But that hypothesis was disproved as cases of “DWI reversal” came to light. The definition of TIA changed from the arbitrary time-based definition to a tissue based one, and our best clinical surrogate for tissue status is MR, which is used to make the distinction between TIA and minor stroke (when clinical symptoms have resolved). However, studies have showed that detecting DWI signal may be contingent on the timing of MR after stroke. Do it early, or lose it..as they say. Also, up to one third of acute infarcts on DWI were not found to have a corresponding FLAIR lesion at 90 days.
In the current study, Kate et al study the temporal evolution of DWI lesions in minor acute ischemic stroke patients in the first 30 days. 114 patients with acute ischemic stroke who had NIHSS <= 3 were enrolled within 48 hours of stroke onset, and underwent 1.5T MRI within 48 hours, at 7 days and 30 days. 2 raters used a semi-automated method to assess DWI and FLAIR lesion volume. A difference of 0.3ml was considered significant when ascertaining infarct volume increase of decrease between the initial DWI lesion volume, and 30 day FLAIR lesion volume. 43% patients had infarct volume reduction at day 7, and 63% at day 30. Infarct growth occurred in 25% patients at day 7 and 14% at day 30. Larger baseline DWI lesion volume correlated with both volume reduction as well as growth. However, only 6 out of 114 (5.3%) patients had complete lesion reversal at 30 days, 5 of whom had reversed at 1 week. A higher mean baseline rADC, and isolated cortical location correlated with reversal. Interestingly, lesion evolution did not correlate with 90 day functional outcome at all.
Although the 5.3% proportion of patients with complete reversal at 30 days is much lower than the prior study which had complete reversal in 1/3rd patients at 90 days, about 2/3rds had lesion volume reduction. It would have been very helpful to have another follow-up MR at 90 days. The 5mm slice thickness I felt was the major limitation of the study, which results in loss of sensitivity. Regardless, the findings do shed light on how minor ischemic lesions evolve on MRI in the early post-stroke period. The more we study MR evolution after stroke, the closer we get to deciphering what the initial DWI lesion means!