Moyamoya disease presenting with repeated ruptures of a lateral posterior choroidal artery aneurysm: illustrative case.

backgroundPeripheral aneurysms may develop along collateral pathways in patients with moyamoya disease (MMD); however, their optimal management remains unclear. The authors report a case of a lateral posterior choroidal artery aneurysm associated with MMD that ruptured three times within a short period, along with a review of the literature. OBSERVATIONS: A 54-year-old woman with MMD, who had remained asymptomatic for 19 years, developed an intraventricular hemorrhage 1 month after periventricular aneurysm dilation was detected on annual imaging follow-up. Rebleeding occurred on days 7 and 10, and vertebral angiography revealed a 6-mm aneurysm in the distal segment of the left posterior choroidal artery. Transarterial embolization using liquid material achieved complete occlusion of the aneurysm; however, the patient developed right hemiparesis due to a left corona radiata infarction and was transferred to a rehabilitation hospital, with a modified Rankin Scale score of 5. LESSONS: Rebleeding from peripheral aneurysms associated with MMD is a predictor of poor prognosis, and spontaneous aneurysm regression during observational management or after bypass surgery requires several months. Accordingly, when such peripheral aneurysms are detected, early revascularization should be planned. However, in cases of rupture, prompt aneurysm-directed treatment, including endovascular or microsurgical intervention, is warranted to prevent clinical deterioration. https://thejns.org/doi/10.3171/CASE26167.