The risk of complications is reportedly high after surgical clipping of aneurysms (ANs) in the middle cerebral artery (MCA-AN), on the medial side of the limen insulae. These are classified as M1 segment aneurysms or short M1 aneurysms. We named these aneurysms medial insulae MCA-ANs and classified them into four types as follows: 1) lenticulostriate artery (LSA) M1 ANs, 2) cortical M1 ANs, 3) short M1 ANs, and 4) anterior temporal artery (ATA) M1 ANs. Subsequently, we analyzed the surgical

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... omes for each type. We had 21 cases of medial insulae MCA-ANs (including 5 ruptured cases) treated with surgical clipping and monitoring using motor-evoked potential (MEP) and indocyanine green video-angiography (ICG-VAG). Of the patients, 8 were men and 13 were women. Their mean age was 66 years (range, 35-83 years). The mean aneurysm size was 5.5 ± 2.2 mm. Of the cases, 3 (14.3%) were LSA M1 ANs; 6 (28.6%), cortical M1 ANs; 10 (47.6%), short M1 ANs; and 2 (9.5%), ATA M1 ANs. Two patients had surgical ischemic complications from the perforating arteries. One had a case of short M1 AN with an asymptomatic left striatum infarction, while the other had a case of cortical M1 AN with postoperative transient paralysis, although the intraoperative MEP decreased. No permanent neurological deficit remained. Medial insulae MCA-ANs are considered hemiparetic complications. Thus, surgeons must accurately judge the type of aneurysm and understand the relationship between the neck and the perforators before clipping.