BACKGROUND: The M1 middle cerebral artery (MCA) commonly bifurcates into M2 superior and M2 inferior segments. However, MCA anatomy is highly variable rendering classification for mechanical thrombectomy trials difficult. This study explored safety and effectiveness of M2 MCA stroke thrombectomy stratified by M2 MCA anatomy.
METHODS: Cases of large vessel occlusion strokes treated by mechanical thrombectomy between February 2016 and August 2022 were reviewed (N = 784). M1 (n = 431) and M2 (n = 118) MCA occlusions were assessed. Among M2 MCA occlusions, only prototypical MCA bifurcation anatomy cases were included (n = 99). Dominance was assessed based on angiography. Procedural and outcome data were compared between M1, M2 superior, and M2 inferior MCA occlusions.
RESULTS: Baseline demographics and periprocedural criteria of M2 superior (n = 56) and M2 inferior (n = 43) occlusion mechanical thrombectomies were comparable. The occluded branch was dominant in 41/43 (95.3%) M2 inferior cases, but in only 37/56 (66.1%) M2 superior cases (P < 0.001). The 90-day favorable functional outcome (modified Rankin Scale score 0-2) and mortality (modified Rankin Scale score 6) rates were 60.0% and 8.9% in M2 superior, 42.9% and 32.6% in M2 inferior, and 44.1% and 26.0% in M1 (n = 431) cases. Compared with M2 superior cases, in M2 inferior cases, favorable outcome rates were lower (P = 0.094) and mortality rates were higher (P = 0.003) and resembled M1 rates (P = 0.750 and P = 0.355, respectively).
CONCLUSIONS: In the setting of prototypical MCA bifurcation anatomy, thrombectomy of dominant M2 inferior occlusions had outcome rates similar to M1 occlusions. In contrast, M2 superior occlusions had significantly lower mortality rates and a trend toward better favorable functional outcome rates.

OBJECTIVE: Our study aimed to evaluate safety, efficacy and clinical outcomes in patients with acute ischemic stroke with occlusion of M2 segment treated with thromboaspiration.
METHODS: A retrospective study was conducted in patients with ischemic stroke of M2 segment undergoing endovascular thromboaspiration. The time period analyzed was from October 2015 until February 2021. Thromboaspiration was performed with AXS Catalyst 5 (Stryker) or AXS Catalyst 6 (Stryker) catheters. The following parameters were assessed: risk factors for ischemic stroke, National Institutes of Health Stroke Scale (entry and discharge), pre-procedural fibrinolysis, pre-procedural and 24-h Alberta Stroke Program Early CT Score, recanalization time, number of passages for recanalization, Thrombolysis in cerebral infarction scale score, periprocedural complications, Modified Rankin Scale score at 90 days from procedure and mortality.
RESULTS: 90 patients were included in the study. The mean age was 75 ± 11.1 with National Institutes of Health Stroke Scale at entry 13 ± 5 and 8 ± 4 at discharge. Pre-procedural fibrinolysis were performed in 40 patients. Pre-procedural Alberta Stroke Program Early CT Score were 8.8 ± 1.3 and 6.9 ± 2.4 after 24 h from the procedure. Time of recanalization from onset of symptoms was 300 ± 82 min. Number of passages for recanalization were 1.8 ± 1.1. Thrombolysis in cerebral infarction scale score ≥ 2b were obtained in 90 % of procedures. After 90 days 33 % of patient obtained an Modified Rankin Scale between 0 and 1 (between 0 and 2 was 40 %). We didn\'t detect any complication in 64 % of cases (subarachnoid haemorrhage in 2 %, HI1 and HI 2 in 15 %, PH1 in 9 % of patients, PH2 in 6 % of patients).
CONCLUSIONS: This paper confirms the usefulness and safety of thrombospiration in patients with ischemic stroke in the M2 segment with low intra-operative risks, high technical success and positive impact on the outcome of the patients.

Extensive randomized controlled clinical trials for endovascular thrombectomy in anterior circulation large vessel occlusions (internal carotid arteries and M1 segment of middle cerebral arteries) have been published over the past decade, but there have not been randomized controlled trials for distal arterial occlusions to date. Distal arterial occlusion randomized controlled trials are essential to decide on patient selection, imaging criteria, and endovascular approach to improve the outcome and reduce complications.
The definition of distal arterial occlusion is however unclear, and we believe that a uniform nomenclature of distal arterial occlusions is essential for the design of robust randomized controlled studies. We undertook a systematic literature review and comprehensive analysis of 70 articles looking at distal arterial occlusions and previous attempts at classifying them as well as comparing their similarities and differences with a more selective look at the middle cerebral artery. Thirty-two articles were finally deemed suitable and included for this review. In this review article, we present 3 disparate classifications of distal arterial occlusions, namely, classical/anatomical, functional/imaging, and structural/calibre, and compare the similarities and differences between them.
We propose the adoption of functional/imaging classification to guide the identification of distal arterial occlusions with the M2 segment starting at the point of bifurcation of the middle cerebral artery trunk/M1 segment. With regards to the anterior temporal artery, we propose that it will be considered a branch of the M1 and only be considered as the M2 segment if it is a holo-temporal artery. We believe that this is a practical method of classification in the time-critical decision-making period.

UNASSIGNED: Mechanical thrombectomy for anterior-circulation large-vessel occlusion has shown benefit; however, the question of whether this technique is safe and effective in the distal vasculature remains unanswered. We sought to compare the outcome data from mechanical thrombectomy of the M2 branches of the middle cerebral artery (MCA) with those of the M1 segment.
UNASSIGNED: We performed a retrospective analysis of prospectively collected data of patients with acute ischaemic stroke undergoing mechanical thrombectomy of isolated M1 or M2 branches of the MCA between August 2008 and August 2016.
UNASSIGNED: We identified 585 patients, 479 with M1 occlusions and 106 with M2 occlusions. The average age was 72 ± 12.8 and 68 ± 13.8 years, respectively (p = 0.007). The baseline Alberta Stroke Program Early Computed Tomographic (ASPECT) score was similar in both cohorts, but patients with M1 occlusions presented with higher mean National Institutes of Health Stroke Scale (NIHSS) scores of 15.7 compared to 11.8 (p < 0.001). There was no significant difference in the average procedure time for each cohort; fewer thrombectomy attempts were required in the M2 cohort (2.3 vs. 1.8, p = 0.0004), but the overall time to recanalization was longer in the M2 cohort (353 vs. 399 min, p < 0.001). Similar rates of successful reperfusion (Thrombolysis in Ischaemic Stroke score [TICI] ≥2b 88.5 vs. 90.5%, p = 0.612) were seen, but food outcome (modified Rankin Scale ≤2) was lower in M1 occlusions (37.2 vs. 54.3%, p < 0.001). Rates of symptomatic intracranial haemorrhage were similar.
UNASSIGNED: Good clinical outcomes can be achieved for both groups with no significant differences in procedure length, final TICI recanalization rates or intracranial haemorrhage between the M1 and M2 cohorts.

OBJECTIVE: Routine sonography of the middle cerebral artery in acute ischemic stroke usually focuses on the main stem (M1 segment). However, stenoses and occlusions affect not only proximal but also more distal vessel branches, such as the M2 segments. Transcranial color-coded duplex sonography allows visualization of these segments; however, a formal analysis and description of normal blood flow values are missing. The purpose of this study was to analyze middle cerebral artery branching patterns with transcranial color-coded duplex sonography and to establish reference flow velocity values in the detectable M2 branches as well as the early temporal M1 branch.
METHODS: Transcranial color-coded duplex sonography in the axial and coronal planes was performed in 50 participants without vascular disease and with a good temporal bone window (ie, fully visible M1 middle cerebral artery segment and A1 anterior cerebral artery segment). We analyzed the course and branching pattern of the M1 segment, including anatomic variants such as an early temporal M1 branch, and measured the length and flow parameters of the detectable M2 branches.
RESULTS: Assessment of 100 hemispheres allowed classification into 3 anatomic patterns: M1 bifurcation (63%), M1 trifurcation (32%), and medial M1 branching into 2 major segments (2%). A clear distinction was not possible in 3 cases (3%). An early temporal M1 branch was detected in the coronal plane in 26%.
CONCLUSIONS: Transcranial color-coded duplex sonography is a useful tool for analyzing anatomic variants and branching patterns of the middle cerebral artery as well as flow characteristics of M2 segments. Therefore, it also has potential to increase the diagnostic yield for the detection of middle cerebral artery disease in these vessel segments.