Aqueductal stenosis Aqueduct of Sylvius stenosis UMLS:C2936786 Aqueduct stenosis Narrowing of aqueduct of Sylvius HP:0002410 Stenosis of the cerebral aqueduct (also known as the mesencephalic duct, aqueductus mesencephali, or aqueduct of Sylvius), which connects the third cerebral ventricle in the diencephalon to the fourth ventricle, which is between the pons and cerebellum. Abnormal brain morphology