RESUMO
BACKGROUND: Bobble-head doll syndrome is a rare and surgically treatable movement disorder characterized by up-and-down (yes-yes) head bobbing occurring at a rate of 2-3 Hz. Side-to-side (no-no) head bobbing is less frequently described. Bobble-head doll syndrome is usually associated with dilation of the third ventricle, but is rarely associated with posterior fossa disease. PATIENT: We describe an infant with fetal hydrocephalus and an arachnoid cyst of the posterior fossa. Endoscopic fenestration of the arachnoid cyst was performed on postnatal day 12. A routine examination at 4 months indicated the infant showed "no-no" type head bobbing, but no other neurological disorder was observed. The third ventricle was dilated during the perioperative period, but not at 2-4 months. In contrast, cerebellar compression decreased gradually and persisted at 4 months. CONCLUSION: Although few patients with bobble-head doll syndrome do not have third ventricle dilation, these patients typically show cerebellar dysfunction. Our findings support the hypothesis that cerebellar dysfunction is present in bobble-head doll syndrome when third ventricle dilation is absent.