Morphological Analysis of the M1 Segment of the Middle Cerebral Artery and Its Implications for Neurosurgical Approaches: A Cadaveric Study.

Anatomical variations of the middle cerebral artery (MCA) and its lenticulostriate perforator branches can confound imaging interpretation and increase ischemic injury risk during various procedures, particularly around the M1 segment, where aneurysms arise. This cadaveric study characterized M1 segment morphology and perforator distribution. Thirty formalin-fixed cerebral hemispheres (27 males and three females) with a mean age of 68 years (ranging from 48 years to 77 years) were dissected under 2.5× magnification with arachnoid removal; M1 origin relative to optic nerve and chiasma were documented, M1 diameter and length were measured, division patterns were recorded, and perforators were quantified on M1 segment of MCA and classified as direct or indirect. M1 length ranged from 8.42 to 24.17 mm (mean 17.13 ± 3.4 mm), and the origin diameter was 2.35 ± 0.51 mm. The MCA originated lateral to the optic chiasma in 25 (83%) and lateral to the optic nerve in five (17%). True bifurcation predominated in 23 (76.7%), with pseudotrifurcation in three (10%), true trifurcation in two (6.6%), and early bifurcation in two (6.6%). Perforator counts varied (0-9), with the highest in the intermediate direct group (mean 4). Forty-seven post-bifurcation perforators were identified, all from the upper division of MCA. Early bifurcation cases lacked medial perforators and showed denser intermediate and post-bifurcation perforation. These findings support identifying perforator-free zones, avoiding perforator injury during clipping, and incorporating cerebral vascular cadaveric dissection into neurosurgical training.