Anatomical Features of Middle Cerebral Artery Bifurcations and those with Aneurysms

To elucidate the anatomical differences between patients with normal MCA bifurcations and those with bifurcations harboring MCA aneurysms, the analysis of three dimensional MRA or DSA were performed. Sixty two patients without intracranial lesions underwent three-dimensional MRA. The width of M2 branches and lateral angles, were measured. Then the DA ratios (width of larger M2/width of smaller M2) and the LA ratios (lateral angle between M1 and larger M2/lateral angle between M1 and smaller M2) were calculated. The DA and LA ratios were also calculated among 54 cases with aneurysms that were performed three dimensional DSA. Moreover, types of aneurysm were classified among 44 cases (20 were ruptured and 24 were unruptured) using three dimensional DSA. When the neck was located on the extension of the midline of the parent artery, it was defined as C type, and when it was not, it was defined as D type. The DA ratio was 1.5±0.4 in normal MCAs and 1.7±0.7 in MCAs with aneurysms which showed significant difference (p<0.05). The LA ratio was 1.3±0.4 in normal MCAs and 2.1±1.4 in MCAs with aneurysms which also showed significant difference (p<0.01). χ2 test revealed that there were significantly more ruptured cases among C type (14/19) compared with D type (10/25) (p<0.05). Normal cerebral artery bifurcations show close to symmetric structures in the M2 branches and the lateral angles, whereas aneurysmal MCAs do not show these symmetries and among cases with aneurysms C type was dominant in ruptured aneurysms.