Background and purpose: The Alberta Stroke Program Early CT Score (ASPECTS) is a validated method of assessing parenchymal ischemic changes, including focal swelling and hypoattenuation. The hypothesis that these signs result from different pathophysiological processes was tested by comparing CT with diffusion and perfusion- weighted MRI.
Methods: MRI and CT were performed, within 2 hours of each other, in 30 ischemic stroke patients <17 hours after symptom onset. Relative apparent diffusion coefficient, relative cerebral blood flow, and relative cerebral blood volume were calculated for individual cortical ASPECTS regions. Regional infarction was assessed on days 3 to 5.
Results: Isolated focal swelling was seen in 25 ASPECTS cortical regions from 6 patients. Cortical hypoattenuation was observed in 25 regions from 11 patients. Median relative apparent diffusion coefficient was significantly lower in hypoattenuated regions (0.84; interquartile range, 0.66 to 0.91) relative to those with focal swelling (0.97; interquartile range, 0.91 to 1.01; P<0.001). Median relative cerebral blood flow in focal swelling regions (81.0%; interquartile range, 70.4 to 93.0) was similar to that of tissue that appeared normal on CT (71.8%; interquartile range, 47.1 to 94.5). In hypoattenuated regions, relative cerebral blood flow was significantly decreased (37.0%; interquartile range, 25.6 to 70.2; P=0.002). Median relative cerebral blood volume was increased (121.1%; interquartile range, 112.0 to 130.3) in focal swelling regions, relative to normal-appearing tissue (94.7%; interquartile range, 62.0 to 114.6; P<0.001), but decreased in hypoattenuated regions (58.9%; interquartile range, 47.5 to 92.7; P=0.012). Infarction occurred in all hypoattenuated regions, but only in 32% of those with focal swelling.
Conclusions: Elevated relative cerebral blood volume and normal relative apparent diffusion coefficient in ASPECTS regions with focal swelling on CT is consistent with penumbral tissue. Isolated focal swelling is not always associated with infarction. These results support removal of focal swelling from the ASPECTS system.