CSF circulates through the Foramen of Monro from the lateral to the third ventricle , down the Aqueduct of Sylvius to the fourth ventricle and into the subarchnoid space via the posterior Foramen of Magendie and the lateral Foramina of Luschka. Some of the CSF travels down the central canal of the spinal cord. In addition, CSF is absorbed via the spinal nerve root pockets into the lymphatic system. Note all results listed above are mid points of quoted ranges. All ventricles are uniformly dilated.
Tumours are also a frequent cause of obstruction.