Congenital odontoid aplasia and posterior circulation stroke in childhood.

Head trauma and vigorous physical activity were followed by delayed-onset posterior circulation stroke in a 5-year-old boy with odontoid aplasia and C1-C2 subluxation. Angiography demonstrated vertebral artery narrowing and occlusion of the left anterior-inferior cerebellar and posterior cerebral arteries. Odontoid aplasia and other atlantoaxial dislocations are treatable causes of posterior circulation insufficiency in childhood; these defects may be overlooked without appropriate radiographic study of the cervical spine using flexion-extension views.