The infarct core is well represented by the acute diffusion lesion: sustained reversal is infrequent

Abstract

Diffusion-weighted imaging (DWI) is commonly used to assess irreversibly infarcted tissue but its accuracy is challenged by reports of diffusion lesion reversal (DLR). We investigated the frequency and implications for mismatch classification of DLR using imaging from the EPITHET (Echoplanar Imaging Thrombolytic Evaluation Trial) and DEFUSE (Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution) studies. In 119 patients (83 treated with IV tissue plasminogen activator), follow-up images were coregistered to acute diffusion images and the lesions manually outlined to their maximal visual extent in diffusion space. Diffusion lesion reversal was defined as voxels of acute diffusion lesion that corresponded to normal brain at follow-up (i.e., final infarct, leukoaraiosis, and cerebrospinal fluid (CSF) voxels were excluded from consideration). The appearance of DLR was visually checked for artifacts, the volume calculated, and the impact of adjusting baseline diffusion lesion volume for DLR volume on perfusion-diffusion mismatch analyzed. Median DLR volume reduced from 4.4 to 1.5 mL after excluding CSF/leukoaraiosis. Visual inspection verified 8/119 (6.7%) with true DLR, median volume 2.33 mL. Subtracting DLR from acute diffusion volume altered perfusion-diffusion mismatch (T(max)>6 seconds, ratio>1.2) in 3/119 (2.5%) patients. Diffusion lesion reversal between baseline and 3 to 6 hours DWI was also uncommon (7/65, 11%) and often transient. Clinically relevant DLR is uncommon and rarely alters perfusion-diffusion mismatch. The acute diffusion lesion is generally a reliable signature of the infarct core.

Figure 1

A patient with apparent diffusion lesion reversal due to infarct atrophy (A) baseline diffusion-weighted imaging (DWI), (B) follow-up T2, (C) composite image with red indicating stable infarction, yellow indicating infarct growth, green indicating diffusion lesion reversal, and blue indicating regions of acute DWI lesion that, rather than ‘reversing,' correspond to cerebrospinal fluid (CSF) or gliosis at follow-up.

Figure 2

A patient with true diffusion lesion reversal (A) baseline diffusion-weighted imaging (DWI), (B) follow-up fluid attenuated inversion recovery (FLAIR), (C) composite image with red indicating stable infarction, yellow indicating infarct growth, green indicating diffusion lesion reversal in the deep white matter, and blue indicating regions of acute DWI lesion that correspond to cerebrospinal fluid (CSF) or gliosis at follow-up.

Figure 3

An example of temporary diffusion lesion reversal in a patient who reperfused with tissue plasminogen activator (tPA). (A) Baseline diffusion-weighted imaging (DWI), (B) DWI 12 hours later (after reperfusion), arrow indicating temporary reversal in the region of the caudate nucleus, (C) follow-up fluid attenuated inversion recovery (FLAIR).