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Objective: The middle cerebral artery (MCA) occlusion is the most commonly treated vessel with mechanical thrombectomy. The MCA is defined in segments. The M1 segment is classically defined as the horizontal segment extending from the internal carotid artery bifurcation to the Sylvian fissure. It is assumed that the MCA bifurcation occurs in the M1-2 junction, and terms M2 occlusion and division occlusion are used indistinctly, however it is not known how often the MCA bifurcation occurs within the M1 segment.Methodology: Consecutive patients undergoing cerebral angiograms were selected between 2011 and 2015. The anatomy of the MCA was classified as classical, when the bifurcation occurs at the M1-2 junction and non-classical when the bifurcation occurs within the M1 segment, having the M1 segment a pre-bifurcation (main trunk) and a post-bifurcation (division) occlusion. Demographics and vascular risk factors were also collected.Results: A total of 500 patients underwent a cerebral angiogram and were studied. The classical pattern was found in 47.5% patients on the left and 53.5% patients on the right. There were no differences between the classical and non-classical anatomical pattern when demographics or vascular risk factors were compared.Conclusion: In our series of patients the non-classical pattern was found in almost 50.0% of the patients undergoing a cerebral angiogram. In the endovascular treatment of acute ischemic stroke, it is necessary to develop a new classification as an M1 occlusion could relate to a post-bifurcation (division) or a pre-bifurcation (main trunk) occlusion and comparison of these groups may lead to confounding results.