A baby is born with an unusually large head. There are no other obvious abnormalities. Ultrasound of the head demonstrates hydrocephalus with marked enlargement of the lateral ventricles. Statistically, at which of the following sites has the obstruction MOST likely to have occurred?
Aqueduct of Sylvius Foramen of Luschka Foramen of Magendie Subarachnoid space near brainstem