2012 年 21 巻 9 号 p. 688-699
Objective : The authors present the anatomical and angiographical details that enable surgeons to quickly locate middle cerebral artery (MCA) aneurysms and to gain proximal control without unnecessary delay or premature rupture.
Materials and Methods : The anatomical dissections were performed in 10 adult cadaveric heads from 1993 to 2011 at the Department of Neurological Surgery, University of Florida. The angiographic and the surgical data were derived from 93 MCA aneurysms operated on by Hung Tzu Wen (HTW) from 1996 to 2012 at the Hospital das Clínicas, University of São Paulo and Hospital Samaritano, Brazil.
Results : MCA aneurysms arise most frequently from the M1 segment and less frequently from M2. From a practical viewpoint, the M1 extends from the carotid bifurcation to the MCA genu (on the basal surface of the cerebrum) with specific topographical relationships along the way, and the M2 extends from the MCA genu to the sylvian or “M” point (on the lateral surface), also with specific topographical relationships. The key for the angiographical analysis of an MCA aneurysm is to establish its topographical relationship to the genu of the MCA. If it is proximal to the genu, it is important to estimate its distance to the carotid bifurcation and to the MCA genu. If it is distal to the MCA genu, it is important to estimate its distance to the genu and to the sylvian point ( “M” point). Also, it is important to evaluate the direction of the dome of the aneurysm, as it indicates the structures to which the dome is attached. The key for locating an MCA aneurysm intraoperatively is the relationship between the MCA genu and the tip of the pars triangularis. The tip of the pars triangularis is a reliable intraoperative landmark (even when it is obscured by severe subarachnoid hemorrhage) and it is located just distal to the MCA genu and approximately 2 cm distal to the sharp transition between the basal and the lateral surfaces of the cerebrum. Once the pars triangularis is identified, the MCA genu can also be quickly estimated and identified, and thereby so will the aneurysm.
Conclusion : The carotid bifurcation, genu of the MCA, and the “M” point on the AP view carotid angiography, and the sylvian triangle on the lateral projection constitute the cardinal landmarks for locating MCA aneurysms angiographically. Correlating the angiographic location of the aneurysm to the pars triangularis of the inferior frontal gyrus constitutes the key for then locating the MCA aneurysm intraoperatively.
