Follow-up study of patients with "unilateral" moyamoya disease.

Sixty-four patients with "unilateral" occlusive disease of the circle of Willis were studied to evaluate progression to bilateral disease. Seventeen patients developed bilateral lesions during a period of 1-7 years after the diagnosis of unilateral lesion. Most of these patients had ischemic attack as the initial episode and had repeated attacks before admission. Young children, mostly less than 10 years of age, tended to develop bilateral lesions within 1-2 years, but adults tended to have only a unilateral lesion. Children or young adults with unilateral occlusive lesion of the terminal portion of the internal carotid artery are likely to develop bilateral disease within 1-5 years.