Feasibility of endovascular treatment for fetal-type posterior cerebral artery aneurysm with P1 segment aplasia: illustrative case.

backgroundAneurysms of the fetal-type posterior cerebral artery (FPCA) are rare and often present with fusiform or dissecting morphology. Unlike the adult-type posterior cerebral artery (PCA), the FPCA can only be accessed through the internal carotid artery, limiting endovascular routes and device options. These anatomical and technical constraints often necessitate parent artery occlusion (PAO) as a treatment strategy; however, it carries a substantial risk of ischemic complications. The authors report a rare case of a ruptured FPCA aneurysm with ipsilateral P1 segment aplasia, treated successfully with stent-assisted coil embolization with preservation of anterograde FPCA flow. OBSERVATIONS: A 79-year-old woman presented with subarachnoid hemorrhage and impaired consciousness. Imaging revealed a fusiform aneurysm along the FPCA and aplasia of the ipsilateral P1 segment. Because of narrow vessel anatomy, dual microcatheter techniques were not feasible. After conservative management, the patient underwent stent-assisted coil embolization via a transcellular approach. The aneurysm was completely obliterated with preserved FPCA flow, and no ischemic complications occurred. LESSONS: A literature review suggests that aneurysms with saccular configuration and proximity to the P2 segment are favorable for selective coil embolization. Given the high risk of thalamic and occipital infarction associated with PAO, preserving FPCA flow should be prioritized when anatomically and technically feasible. https://thejns.org/doi/10.3171/CASE25556.