Moyamoya isease is an extremely rare disorder in most parts of the world except in Japan, where the overall incidence is higher (0.35 per 100,000). The pathogenesis of Moyamoya disease is unknown. Moyamoya disease is characterized by progressive intracranial vascular stenoses of the circle of Willis, resulting in successive ischemic events. Hemorrhagic events can also occur. The condition leads to irreversible blockage of the carotid arteries to the brain as they enter into the skull. It is a disease that tends to affect children and adults in the third to fourth decades of life. In children it tends to cause strokes or seizures. In adults it tends to cause bleeding or strokes. The clinical features are cerebral ischaemia (strokes), recurrent transient ischaemic attacks (TIAs or "mini strokes"), sensorimotor paralysis (numbness in the extremities), convulsions and/or migraine-like headaches.