Objects: Some cases of unilateral involvement have angiographic findings on the affected side which resemble those of definite cases of moyamoya disease (MMD). We analyzed these cases to determine whether the entity "unilateral MMD" actually exists and whether unilateral involvement represents only the early phase of the pathologic process found in definitive bilateral disease.
Methods: Between 1988 and 2000, seven cases of unilateral MMD were evaluated. The male-to-female ratio was 2:5, mean age was 5.1 years (7 months to 8 years), and mean follow-up duration was 64.7 months. The presenting symptoms of these cases were similar to those of definite MMD, and no familial occurrence was found. Two of the seven unilateral MMD cases showed progression to bilateral involvement. However, the remaining cases showed no evidence of contralateral progression during the follow-up period.
Conclusions: Most cases of unilateral MMD seem to be an unusual form of stenoocclusive process of the proximal intracranial arteries, distinguishing the condition from definite MMD. Surgical treatment on the symptomatic side and close observation for signs of bilateral involvement are necessary.