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.