The purpose of this study is to investigate the long-term outcomes of conservative management in patients with moyamoya disease and their first-degree relatives, and provide potential pathogenesis of moyamoya disease.

Moyamoya disease (MMD) is a chronic occlusive-stenosis cerebrovascular disease that characterized by the stenosis of internal carotid artery termination and the formation of net-like vessel. It is a multifactorial disease caused by genetic, inflammatory, immunological and other environmental factors. The specific pathogenesis of MMD is still unclear. The treatment modalities of revascularization and conservative management have been used in patients with MMD. However, the long-term outcomes of MMD with conservative management remain unknown. Also, some first-degree relatives who are carriers of genetic variants occasionally manifest with intracranial arterial stenosis. Therefore, it is significant to detect the long-term outcomes of conservative treatment in MMD patients and their first-degree relatives, and thus provide potential pathogenesis of MMD.

Inclusion Criteria:

1. Patients with age between 2-60 years;
2. A clinical diagnosis of moyamoya disease, including unilateral and bilateral disease.
3. Patients are medically treated with antiplatelets, antiepileptics, antihypertensives and vasodilators depending on the presentation.
4. Capable of understanding the purpose and risk of the study and has signed the informed consent. If the participant is not capable of this at the time of enrollment, a legally authorized representative will provide written informed consent in accordance with all regulations.
5. Ability to comply with study follow-up.

Exclusion Criteria:

1. Concomitant other diseases, including systemic vasculitis, neurofibroma, meningitis, sickle cell disease, down's syndrome, and previous basilar radiotherapy.
2. Patients with cardiogenic embolism, including a history of atrial fibrillation, valvular disease or cardiac valve replacement.
3. Patients are allergic to the contrast agents.
4. Patients are treated with direct, indirect, or combined revascularization depending on the presentation.
5. Physical or subjective failure to cooperate with the examination or serious comorbid diseases.
6. Patients are unable or unlikely to return for follow-up visits.
7. Any other reasons that, in the opinion of the investigators, make the participant unsuitable for enrollment.

Consecutive patients diagnosed with MMD in Beijing Tiantan Hospital will be recruited. Eligibility will be determined through a checklist of inclusion and exclusion criteria. Relatives will be recruited from the first-degree relatives of patients with MMD.