04:12 PM Abstract No. 168 M2 Frontal and Parietal Division Angles Impacting Success of Mechanical Thrombectomy

Abstract

Vessel anatomy is the cornerstone of endovascular therapy, including in mechanical thrombectomy (MT). The horizontally orientated M1 segment of the MCA commonly terminates in a bifurcation. The M2 segment is made up of a frontal division coursing cephalic to supply the frontal convexity and a parietal division which appears as a continuation of the M1 coursing inferiorly to supply the temporoparietal lobes. We have demonstrated the rate of successful reperfusion following MT is significantly greater in parietal division than frontal division occlusions (unpublished work). Our current hypothesis is that the differences in success are due to a less obtuse angle of the frontal versus parietal division. A single-center retrospective study was conducted to identify isolated frontal and parietal M2 branch occlusions from September 2012 to April 2018. Occlusions involving the M1 segment, distal MCA (M3 and M4 divisions), ACA, ICA and posterior cerebral circulation were excluded. 3D renderings from preprocedural CT angiography of the head (MRA reformats were used for a single patient) were utilized to assess vessel anatomy. The angle between the conterminous segment of the distal M1 and of each M2 division were measured from the healthy non-occluded side. The angle between the M1 and parietal division was designated M1/parietal angle. A second angle between the M1 and frontal division was designated M1/frontal angle. Twenty nine out of 364 endovascularly treated cases had isolated parietal or frontal M2 occlusions. Of these, 23 met our criteria; 17 subjects were in the parietal cohort and 6 subjects in the frontal cohort. Mean age of patients was 67.7. There was a larger mean M1/parietal angle than M1/frontal angle in the parietal cohort (146.2° vs 116.3, p = <0.0001) and frontal cohort (147.7 vs 116.5, p = 0.013). A less obtuse angle of the frontal M2 division can account for an increased failure of recanalization. Although it may be difficult to determine the angle on the occluded side due to nonvisualization of the vessel, angle measurement on the healthy side correlates with success of mechanical thrombectomy.