Another term for aqueduct of Sylvius.This ventricle is continued cranially into the cerebral aqueduct of the midbrain....
The fourth ventricle communicates with the third ventricle via a narrow tube, the cerebral aqueduct, which runs up through the midbrain.
Transependymal flow (best appreciated on the proton density images) is also seen and consistent with obstruction of the cerebral aqueduct from compression of the midbrain by uncal herniation.