Coil embolization via donor superficial temporal artery for de novo aneurysm associated with revascularization surgery in a patient with moyamoya disease: illustrative case.

backgroundDe novo aneurysm formation at the anastomotic site of superficial temporal artery (STA)-middle cerebral artery (MCA) bypass surgery for moyamoya disease (MMD) is an exceptionally rare but clinically significant complication. Previously reported cases were treated with direct microsurgery, where preservation of established pial synangiosis was a major concern. The authors herein report the first case successfully treated with endovascular coil embolization, achieving complete preservation of pial synangiosis and a favorable clinical outcome. OBSERVATIONS: A 53-year-old man had undergone combined revascularization surgery for MMD 14 years earlier. Although the patient remained asymptomatic, follow-up MR angiography revealed a gradually enlarging de novo aneurysm with daughter sac formation at the anastomotic site. Cerebral angiography demonstrated a narrow-neck saccular aneurysm and a well-developed donor STA, allowing access for endovascular treatment. A microcatheter was advanced into the aneurysm via a distal access catheter placed in the STA, and coil embolization with five coils achieved complete obliteration. The patient recovered uneventfully, and follow-up imaging confirmed the durable occlusion. LESSONS: Endovascular therapy represents a valuable treatment option for de novo aneurysm after STA-MCA anastomosis in MMD, as it completely preserves established collaterals. Careful patient selection and meticulous procedural planning are essential to ensure safety and efficacy. https://thejns.org/doi/10.3171/CASE25666.