The main purpose of this study is to compare two types of treatment of hydrocephalus: placement of a ventriculoperitoneal (VP) shunt versus an endoscopic third ventriculostomy (ETV). A second goal of this study will be to understand how the two different types of procedures, VP shunt versus ETV, affect brain blood flow and pressures. Understanding these changes is important because the investigators hope is to someday be able to predict who will better respond to one procedure or another.