Fetal-type posterior cerebral artery (fPCA): association with posterior communicating artery aneurysm rupture and treatment outcomes, with practical surgical risk-mitigation strategies.

BACKGROUND: The fetal-type posterior cerebral artery (fPCA) is a circle of Willis variant in which the posterior cerebral artery (PCA) territory is supplied mainly by the internal carotid artery (ICA) through a dominant posterior communicating artery (PComA), with a hypoplastic or absent ipsilateral P1 segment. This carotid dependence alters collateral reserve and the hemodynamics of the ICA-PComA junction, with consequences for aneurysm formation, rupture, and procedural safety. METHODS: We performed a narrative review. We searched PubMed/MEDLINE and Scopus for English-language studies on fPCA and PComA aneurysm formation, rupture, and microsurgical, endovascular, and revascularization outcomes, prioritizing cohort series, comparative studies, and quantitative reports. This is a narrative synthesis and not a systematic review or meta-analysis. RESULTS: fPCA is overrepresented among patients with PComA aneurysms, with a prevalence on the aneurysmal ICA of about 42% versus 19% contralaterally (odds ratio [OR] 3.04), and the association is specific to the ICA-PComA location (OR 2.76). Its effect on rupture is less consistent: fPCA is an independent predictor in some series (OR 2.10) and on radiomic analysis (OR 3.85) but not in others, with a pooled unadjusted OR of 1.57 (95% CI 1.13-2.19) in meta-analysis. Flow diversion achieves complete occlusion in only about 42-44% of fPCA-associated aneurysms versus 78-82% without fPCA. CONCLUSIONS: fPCA is an anatomic modifier of both aneurysm risk and treatment. Preservation of the dominant PComA trunk is the unifying surgical and endovascular principle. Heterogeneous definitions limit cross-study comparison, and standardized reporting of complete versus partial fPCA is needed.