Growth pattern of ischemic lesions with different initial volume in a permanent middle cerebral artery occlusion model
Background and Purpose: Diffusion-weighted imaging (DWI) allows measurement of ischemic lesions in a real-time manner and is used increasingly for evaluation of stroke therapy. This study was to determine if lesion growth is different when the initial lesion volumes on DWI are different after permanent middle cerebral artery occlusion (MCAO) in rats. Methods: Twelve Sprague-Dawley male rats were subjected to permanent MCAO with the intraluminal suture method. DWI was performed at 30, 60, 90, 150, 210, and 270 minutes after occlusion. The ischemic lesion areas were determined by visually tracing the hyperintense border on DWI, and the lesion volumes were calculated by multiplying the areas by the slice thickness. Based on the initial lesion volume at 30 minutes, the rats were evenly assigned to two groups: group A with smaller initial volume (<130 mm3, n=6) and group B with larger initial volume (≥130 mm3, n=6). Results: The initial lesion volumes at 30 minutes were significantly different between two groups (106±14 mm3 vs 189±38 mm3, p<0.001), and the lesion volumes were also different thereafter (189±35 mm3 vs 270±76 mm3 at 270 minutes, p=0.04). The absolute increased volumes at 270 minutes, however, had no difference between two groups (84±32 mm3 in group A and 82±44 mm3 in group B, p=0.93). The percent increase of the lesion volume in group A was bigger than that in group B (80±30% vs 42±17% at 270 minutes, p=0.02). Conclusions: The growth rate of the ischemic lesion is larger if the initial lesion volume is smaller, but the absolute increase of the lesion volume is similar regardless of the difference of the initial lesion volume. These findings are of importance in evaluating the efficacy of stroke therapy when the initial lesion volumes are different.