A novel classification of the basilar artery bifurcation height and the impact of fetal-type posterior cerebral artery: a radioanatomical study with implications for neurosurgical planning

Purpose The vertical location of the basilar artery bifurcation (BAB) is a crucial factor in determining the best surgical approach for basilar tip (BAT) aneurysms. Although anatomical variants, such as the fetal-type posterior cerebral artery (FPCA), have been linked to aneurysm formation, their impact on BAB height remains unclear. Methods A retrospective anatomical-imaging analysis of 250 high-resolution computed tomography angiograms (CTAs) was conducted to measure the vertical distance from the BAT to the clinoidal line (CL). A dominant posterior communicating artery and/or a hypoplastic or absent P1 segment defines the FPCA. Results BATs were classified into four types based on their BAT-CL distance, with Type 2 BATs (within ± 5 mm of the CL) being the most common. The mean BAT-CL distance was + 2.88 ± 4.8 mm. An FPCA was identified in 74 patients (29.6%). The BAT was significantly lower in all fetal-type subgroups than in patients with typical PCA anatomy (p < 0.005). Bilateral FPCA exhibited the lowest BAT-CL distance (-0.9 ± 3.2 mm). An FPCA is significantly associated with a caudally positioned BAT. Conclusions This finding can assist in surgical planning by predicting aneurysm height based on vascular configuration. In such cases, the pretemporal trans-cavernous approach through extended pterional craniotomy may offer safer and more direct access, thereby reducing surgical morbidity. These results support incorporating vascular variants in preoperative assessments to optimize personalized neurosurgical strategies.