Purpose <p>This study aimed to identify predictive factors for incomplete occlusion in posterior communicating artery (PCoA) aneurysms after endovascular treatment (EVT) and investigate the role of fetal-type posterior cerebral artery (fPCA) in occlusion outcomes using quantitative digital subtraction angiography (QDSA).</p> Methods <p>We analyzed 287 patients with 292 PCoA aneurysms treated with EVT between 2016 and 2022. Aneurysms were categorized into incomplete (<i>n</i> = 49) and complete (<i>n</i> = 243) occlusion groups based on follow-up DSA. Clinical, morphological, and hemodynamic parameters from QDSA were compared, and independent risk factors were identified via multivariate logistic regression. Predictive performance was evaluated using area under the curve (AUC) and subgroup analysis with Benjamini-Hochberg correction for fPCA effects.</p> Results <p>Independent risk factors for incomplete occlusion included size (<i>p</i> &lt; 0.001, OR = 1.127), neck cerebral blood flow (CBF) (<i>p</i> = 0.001, OR = 4.024), simple coiling (<i>p</i> &lt; 0.001, OR = 4.635), ruptured status (<i>p</i> = 0.002, OR = 3.281), and fPCA (<i>p</i> = 0.030, OR = 2.218). AUCs for the combined model, size, neck CBF, simple coiling, ruptured status, and fPCA were 0.822, 0.721, 0.708, 0.656, and 0.603, respectively. In the fPCA subgroup, ruptured status, neck CBF, neck cerebral blood volume (CBV), PCoA CBF, and PCoA CBV showed significance, while in the non-fPCA subgroup, only simple coiling and size remained significant.</p> Conclusion <p>Size, neck CBF, simple coiling, ruptured status, and fPCA are independent risk factors for incomplete occlusion in PCoA aneurysms treated with EVT. fPCA likely influences incomplete occlusion through hemodynamic changes.</p>