I know that 1 in 500 children are born w/hydrocephalus, but what's the statistics for acquired hydro? percentage of people with vp shunts?

Acquired hydrocephal: Hydrocephalus at birth is usually secondary to an intracranial hemorrhage at birth or before birth. The most common form later is secondary to stenosis (narrowing) of one of the outflow channels for cerebrospinal fluid we make approximately 500cc per day and need to reabsorb 500cc per day. If you have a shunt and the shunt continues to function properly you should not get hydrocephalus.

Unknown: Hydrocephalus has many causes. Most are in the chilhood age groups and are congenital. The age peak for adults is in the 70's and 80's. Tumors, trauma, and brain hemorrhage also cause hydro in adults and there are no known registries that can give you a number. You could search codman and johnson and johnson websites for hydro valve manufacturers. They may have numbers of valves sold.