What is normal pressure hydrocephalus, the brain disorder affecting Billy Joel?

Singer Billy Joel said Friday he was recently diagnosed with normal pressure hydrocephalus and that it was affecting his hearing, vision and balance. What is the brain disorder and how can it be treated?
Source: What is normal pressure hydrocephalus, the brain disorder affecting Billy Joel? (https://www.cbc.ca/news/health/normal-pressure-hydrocephalus-1.7542276?cmp=rss)