Neurosurgeons at Primary Children's Medical Center, University of Utah, Salt Lake City, evaluated factors that are associated with rupture of arachnoid cysts (intracystic hemorrhage, subdural hematoma, or adjacent subdural hygroma) in children with previously asymptomatic arachnoid cysts. Two unruptured nonhemorrhagic controls were matched to each case. A total of 309 patients with treated and untreated arachnoid cysts were identified between 2005 and 2010, an institutional prevalence of 1.9%. After exclusion of surgical cases, 232 remained in the study. Risk factors evaluated included arachnoid cyst size, recent head trauma, and altitude at residence. Fourteen cases (6%) presented with either rupture or hemorrhage. Larger cyst size and diameter was significantly associated with cyst rupture/hemorrhage (p<0.001). Recent history of trauma was also associated with outcome (p<0.01). Altitude was not a risk factor. Children with rupture/hemorrhage were more likely to present with headache or signs or symptoms of raised intracranial pressure, including midline shift. None suffered neurological sequelae. 
COMMENT. Cyst size and recent head trauma are risk factors for cyst rupture.