The terms 'communicating' and 'non-communicating' describe whether a dye injected into the ventricular system reaches the lumbar subarachnoid space; their import is to describe whether there is communication between the ventricular system and the subarachnoid space of both the cerebral hemispheres and the spinal cord. With the use of lumbo-peritoneal shunts these have more relevance today than previously; [...]