Difficulties in diagnosing congenital posterior fossa fluid collections after shunting procedures.

The differential diagnosis of retrocerebellar fluid collections in infants is important because of the prognostic implications. Usually the diagnoses are easy; however, shunting of the lateral ventricles or of the fluid collections may alter the appearance of the lesions, precluding accurate diagnosis. Under such circumstances a careful study of all the sequential radiologic studies is necessary.