The cause of Moyamoya disease is unknown, and its onset is most common in children. The pathological and anatomical basis of the disease is characterized by progressive stenosis or occlusion of the terminal internal carotid artery or its branches at the beginning of the anterior and middle cerebral arteries, with the formation of an abnormally slender neovascular network at the base of the brain, and extensive vascular anastomosis between the intracranial arteries and between the intracranial and extracranial arteries. Clinical manifestations Adolescent type: ischemic symptoms are common, including transient ischemic attack (TIA), reversible ischemic neurological deficits (RINDs), and severe cerebral infarction. It can be triggered by exertion or hyperventilation (e.g., playing a musical instrument, crying). The pathological changes are usually evident around the age of 10 years and gradually stabilize thereafter. Typical clinical manifestations include alternating limb hemiparesis. It may also manifest as seizures, sensory disturbances, mental retardation and headaches. Adult form: Bleeding is more common. It may manifest as stroke-like seizures, epileptic seizures and involuntary movements. It is most often produced by rupture of a fragile smoke-like vessel at the base of the skull or an accompanying microaneurysm. The site of hemorrhage is hemorrhage in the basal ganglia, thalamus or ventricles or with subarachnoid hemorrhage (SAH). However, the definition of hemorrhagic and ischemic types is not absolute; hemorrhage and ischemia often occur together, sequentially in the same patient, with the common cause being the difficulty of the fibrous vascular network to continue the normal cerebral blood supply and the vulnerability of anatomically defective microvessels to rupture and hemorrhage. Therefore, regardless of the ischemic or hemorrhagic type, immediate intracranial and extracranial arterial communication should be established to relieve the pressure on the blood supply to the ciliovascular network. Moyamoya disease (MSD) has an unknown etiology and is most common in children. It is characterized by progressive stenosis or occlusion of the end of the internal carotid artery or the beginning of the anterior and middle cerebral arteries, the formation of an abnormally thin neovascular network at the base of the brain, and the formation of extensive vascular anastomoses between the intracranial and extracranial arteries. Clinical manifestations Adolescent type: ischemic symptoms are common, including transient ischemic attack (TIA), reversible ischemic neurological deficits (RINDs), and severe cerebral infarction. It can be triggered by exertion or hyperventilation (e.g., playing a musical instrument, crying). The pathological changes are usually evident around the age of 10 years and gradually stabilize thereafter. Typical clinical manifestations include alternating limb hemiparesis. It may also manifest as seizures, sensory disturbances, mental retardation and headaches. Adult form: Bleeding is more common. It may manifest as stroke-like seizures, epileptic seizures and involuntary movements. It is most often produced by rupture of a fragile smoke-like vessel at the base of the skull or an accompanying microaneurysm. The site of hemorrhage is hemorrhage in the basal ganglia, thalamus or ventricles or with subarachnoid hemorrhage (SAH). However, the definition of hemorrhagic and ischemic types is not absolute; hemorrhage and ischemia often occur together, sequentially in the same patient, with the common cause being the difficulty of the fibrous vascular network to continue the normal cerebral blood supply and the vulnerability of anatomically defective microvessels to rupture and hemorrhage. Therefore, regardless of the ischemic or hemorrhagic type, intracranial and extracranial arterial communication should be established immediately to relieve the pressure on the blood supply to the ciliovascular network.