CHARACTERISTICS OF PTERIONAL ROUTES TO BASILAR BIFURCATION ANEURYSM

IN AN ATTEMPT to clarify the characteristics of the pterional routes t o the basilar bifurcation aneurysm, 65 consecutive surgical cases were retrospectively analyzed concerning the size of the aneurysm, the hei ght of the aneurysm neck, the length of the clip blades, and the direc tion of clip application. Clipping was performed through the pterional route in 59 cases consisting of 14 opticocarotid and 45 retrocarotid routes. A subtemporal approach was performed for six low-positioned an eurysms. The opticocarotid approach was undertaken because of the foll owing situations: 1) laterally protruded and/or highly sclerotic inter nal carotid artery (n = 8); 2) long, redundant A1 segment (n = 3); 3) an associated aneurysm of the internal carotid artery obstructing the retrocarotid space (n = 2); and 4) a short and/or large posterior comm unicating artery obstructing the retrocarotid space (n = 1). The range in height of the aneurysm neck was narrower in the opticocarotid appr oach (1 similar to 10 mm) than in the retrocarotid approach (-7 simila r to 15 mm). The direction of clip application on the axial plane was more anteriorly deviated in the opticocarotid approach (41.4 +/- 12.8 degrees from the glabella-inion line) than in the retrocarotid approac h (58.8 +/- 11.1 degrees; P = 0.01). The retrocarotid route (n = 45) w as further subdivided into the medial or lateral retrocarotid routes, depending on the medial or lateral side to the posterior communicating artery, respectively. The medial retrocarotid approach (n = 9) made i t possible to reach relatively high-positioned aneurysms (7.0 +/- 3.9 mm) compared with the lateral retrocarotid approach (4.2 +/- 4.7 mm; n = 29). The direction of clip application on the axial plane was restr icted in the medial retrocarotid approach between 53 and 75 degrees, w hereas that in the lateral retrocarotid approach was between 37 and 92 degrees. The aneurysm size in the cases where the bridging vein was f inally sectioned from the temporal lobe (the temporopolar approach; 10 .0 +/- 4.1 mm; n = 11) was significantly larger than in those where th e vein was not sacrificed in the retrocarotid route (6.9 +/- 3.3 mm; n = 34). Knowing the characteristics of each approach route is essentia l to achieve successful clipping. Furthermore, combining more than two approach routes is valuable to observe the anatomical relationship ar ound the aneurysm neck from the variable directions.