Hi,
To my knowledge, hydrocephalus of any kind for any reason is handled by a shunt or (I know you don't want to hear it) tumor removal. Shunts can be different: lumbar-peritoneal (LP) or ventricular-peritoneal (VP). It is a short surgery, no big deal. I had post-surgical hydrocephalus when CSF was not draining properly, so they implanted a shunt to help CSF drain better and prevent its build-up in the brain which otherwise is called hydrocephalus.
Another way they can go is to surgically remove the tumor which is obstructing CSF drainage. I heard of both scenarios happen (shunt post radiation and surgery post radiation) but only your doctors can judge what is better.
The danger of untreated hydrocephalus is long-term brain damage and I mean the real one, with memory and other cognitive and movement issues. As CSF builds in the brain (hydrocepahlus exists or progresses), it compresses ALL brain, including cerebrum, which is usually not involved in AN and thus creates issues that AN usually does not cause.
Hydrocephalus can cause excruciating headaches and they usually motivate the patient (and the doctor) to seek treatment, however, if there are no headaches, it can go untreated with long-term consequences as the result. Regardless of your symptoms, if I were you, I would insist on treatment ASAP. After all, this is your head and your life.
Eve