[en] In order to determine the distribution and frequency of infarction due to occlusion or stenosis of middle cerebral artery (MCA) trunk, 223 patients with occlusion or stenosis at levels from M1 to M2 were studied according to angiographic (AG) findings and computed tomography (CT) with emphasis on the mechanisms of obstruction, such as embolism. Patients were divided into 4 groups; 84 cases of M1 occlusion (G-I), 88 cases of M2 occlusion (G-II), 31 cases of M1 stenosis (GII) and 20 cases of M2 stenosis (G-IV). CT findings, which revealed LDA in 199 patients, were classified into 8 types on the basis of the branch artery territory as follows; S+D type (60 cases), D+WB type (47 cases), S type (45 cases), B type (18 cases), WB type (15 cases), D type (10 cases), H type (3 cases) and WM type (1 case). Though the S+D type and D+WB type were seen frequently in G-I. When patients with embolism are included in the groups, 85% and 77% were thought to be due to M1 occlusion, respectively. While a half of the S+D types were caused by embolism, almost none of the D+WB types were due to embolism. This suggested that infareted area in nonembolic obstruction at the level of M1 creates smaller lesion with a sufficient collateral circulation through leptomeningeal anastomoses. Eighty percent of S type lesions were seen in M2 lesion (G-II, IV). All the B types, in which the LDA was localized to the subcortical white matter, were seen in nonembolic obstruction of G-II-IV. WB type, seen in G-I-III, and D type, were seen in 9% of M1 lesions and were infrequently caused by embolism. WM type and H type were considered to be associated with the other arterial lesions. (J.P.N.)