M1 segment morphology is associated with far lateral lenticulostriate arteries in middle cerebral artery bifurcation surgery: a cadaveric and clinical anatomic study.

Lenticulostriate arteries (LSAs) arising from the middle cerebral artery (MCA) bifurcation or M2 segment and coursing medially toward the anterior perforated substance (APS), defined here as "far lateral LSAs", represent a surgically vulnerable anatomical variant during procedures such as MCA aneurysm clipping and insular glioma resection. When preoperative imaging is limited, intraoperative recogniton of these branches becomes important. We sought to identify M1 segment morphologic features associated with the presence of far lateral LSAs through analysis of 42 cadaveric hemispheres and 14 clinical cases. Associations between far lateral LSAs and M1 segment length and configuration were evaluated using microsurgical observation and angiographic analysis. In the cadaveric series, far lateral LSAs were identified in 23 cases (54.8%) and were significantly more frequent in hemispheres with short M1 segments (< 11.5 mm; 39.1% vs. 5.3%, p = 0.001) and in those with upward or straight downward M1 configurations (p < 0.0001). Notably, far lateral LSAs were not visualized on 3D rotational angiography in 30% of clinical cases. These findings demonstrate that a short M1 segment with an upward or straight downward orientation is associated with the presence of far lateral LSAs. This relationship may reflect the embryological development of the MCA and LSAs through the fusion and regression primitive lateral striate arteries. While meticulous intraoperative dissection remains essential, awareness of M1 morphology may help neurosurgeons anticipate far lateral LSAs when preoperative visualization of perforators is limited.