Background: Peripheral aneurysms are known to be a source of intracranial hemorrhage in patients with moyamoya disease. However, the natural history of ruptured peripheral aneurysms remains unclear. Some regress spontaneously, whereas others may rebleed. Direct treatments, such as surgical or intravascular treatment of the peripheral aneurysm, can have a risk of severe neurologic complications owing to the depth of the operative field and the fragility of the parent artery. A careful treatment policy is required. Case Description: In a 29-year-old man with moyamoya disease with intraventricular hemorrhage, rupture of a right anterior choroidal artery aneurysm was diagnosed by cerebral angiography. The aneurysm was approximately 4 mm in size and existed in the plexal segment of the right anterior choroidal artery. Endovascular embolization of the aneurysm was planned. However, repeat angiography 3 weeks after aneurysm diagnosis demonstrated complete resolution of the aneurysm. Such short-term disappearance of an aneurysm is remarkably rare. We believe that the aneurysm was thrombosed for a brief period considering the slow blood flow detected inside the aneurysm during the initial angiography. The patient was discharged with no neurologic deficit and has remained recurrence-free for >1 year. Conclusions: Given that spontaneous resolution of an aneurysm may occur in a short period of time, we suggest that conservative treatment be considered as an option for ruptured peripheral aneurysms associated with moyamoya disease when direct treatment is risky.
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