Characteristics of Pterional Routes to Basilar Bifurcation Aneurysm

Abstract

IN AN ATTEMPT to clarify the characteristics of the pterional routes to the basilar bifurcation aneurysm, 65 consecutive surgical cases were retrospectively analyzed concerning the size of the aneurysm, the height of the aneurysm neck, the length of the clip blades, and the direction 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 aneurysms. The opticocarotid approach was undertaken because of the following situations: 1) laterally protruded and/or highly sclerotic internal 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 communicating artery obstructing the retrocarotid space (n = 1). The range in height of the aneurysm neck was narrower in the opticocarotid approach (1∼10 mm) than in the retrocarotid approach (−7∼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 approach (58.8 ± 11.1 degrees; P = 0.01). The retrocarotid route (n = 45) was 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 it 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 restricted in the medial retrocarotid approach between 53 and 75 degrees, whereas that in the lateral retrocarotid approach was between 37 and 92 degrees. The aneurysm size in the cases where the bridging vein was finally sectioned from the temporal lobe (the temporopolar approach; 10.0 ± 4.1 mm; n = 11) was significantly larger than in those where the vein was not sacrificed in the retrocarotid route (6.9 ± 3.3 mm; n = 34). Knowing the characteristics of each approach route is essential to achieve successful clipping. Furthermore, combining more than two approach routes is valuable to observe the anatomical relationship around the aneurysm neck from the variable directions.