Hydromyelia associated with a posterior fossa cyst.

There are rare reports of children with hydromyelia in association with arachnoid cysts at the foramen of Magendie, and these cases have uniformly been associated with hydrocephalus. We report a case of a 45-year-old woman with a posterior fossa cyst associated with hydromyelia and normal ventricles. This was successfully treated with a cystoperitoneal shunt. We believe this unusual condition is of interest in elucidating potential mechanisms of hydromyelia.