To the Editor Recent data from randomized clinical trials1 provide clear evidence that endovascular treatment for acute ischemic stroke because of large vessel anterior circulation occlusion improves clinical outcomes for patients. These studies reported that most patients had an occlusion of the first segment (M1) of the middle cerebral artery and less than 10% in the M2 segment. The retrospective multicenter study conducted by Sarraj et al2 reports that endovascular treatment is safe and effective for an occlusion of the M2 segment. However, the literature reports different definitions for the M1 and M2 segments, which may lead to confusion. Some considerations on the topographic anatomy of the middle cerebral artery might be therefore useful. This ambiguity arises because the definition of M1 and M2 differs according to whether the classification is “clinical ultrasonographic” or “anatomic angiographic.”3 In the former, the anatomic boundary between M1 and M2 is defined by the bifurcation (or dichotomous branching in its upper frontal and temporal inferior branches, wherever it might fall [ie, in the horizontal or vertical tract]). In the latter, which should be adopted to avoid the present uncertainty,4 the anatomic limits are represented by the middle cerebral artery “genu,” where it enters the Sylvian cistern at the level of the limen insulae (Figure, A and B).
Morelli N, Rota E, Michieletti E. Not All Middle Cerebral Artery M2 Segments Are the Same. JAMA Neurol. 2017;74(4):487-488. doi:10.1001/jamaneurol.2016.6171