Cerebral aqueduct
The cerebral aqueduct is roughly circular in transverse section, and measures 1-2 mm in diameter.[2] Rostrally, it is continuous with the third ventricle, commencing just inferior to the posterior commissure.[1] The superior and inferior colliculi that make up the corpora quadrigemina are situated posteriorly to it.[3] The cerebral aqueduct, as other parts of the ventricular system of the brain, develops from the central canal of the neural tube, and it originates from the portion of the neural tube that is present in the developing mesencephalon, hence the name "mesencephalic duct.Such narrowing can be congenital, arise via tumor compression (e.g. pinealoblastoma), or through cyclical gliosis secondary to an initial partial obstruction.