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.

The management of normal pressure hydrocephalus (NPH) is challenging due to diagnostic uncertainties and high treatment risks. To date, there are no evidence-based treatment standards for this disorder. Our long-term goal is to improve the outcome of NPH improving our understanding of cerebrospinal fluid (CSF) hydrodynamics. The Specific Aims are to 1) determine the value of a high volume tap test, and 2) determine whether intracranial hemo/hydrodynamic variables, measured before a shunt operation, support the tuned-dynamic absorber model of intracranial pressure dynamics.

The study's Aim relates to modeling the complex hydro- and hemodynamics of intracranial physiology-pathology. We hypothesize that current hydrocephalus models are over-simplistic and that shunt-induced hydrodynamics are better modeled based on ICP waveform characteristics and the application of novel dynamic models. Much of the data for this Aim will be passively recorded during the routine care of the patient. In essence, we are only adding noninvasive MRI studies and TCD (transcranial Doppler) studies.

The experimental methodology is aimed at altering the intracranial compartment compliance by placing the patient in various positions so that these phase differences can be detected. The simplest way to alter intracranial compliance is to make postural changes. When a patient is in the Trendelenburg position, venous outflow out of the brain is hindered resulting in an increase in ICP and presumably a reduction in compliance. Conversely, raising the head of bed to 60 degrees will result in the opposite effect. The second mechanism of altering compliance (and ICP) will occur as a result of treating the hydrocephalus with a CSF shunt. Because we are able to study hydrocephalus patients prior to shunting as part of their diagnostic workup, we create a new state with the shunt that will allow us to further characterize the intracranial system.

Inclusion Criteria:

• Findings of gait/balance disturbance must be present, plus at least one other area of impairment in cognition, urinary symptoms or both
• Minimum duration of symptoms of at least three months, progression over time, and no other neurological, psychiatric or general medical conditions that are sufficient to explain the presenting symptoms
• MRI or CT performed after onset of symptoms must show evidence of ventricular enlargement (Evan's index > 0.3) not entirely attributable to cerebral atrophy or congenital enlargement
• Criteria for shunt placement: we place greatest emphasis on the results of the temporary CSF drainage trial. Patients who experience a temporary improvement in neurological function (gait, bladder control, and/or cognition) are offered a shunt operation. For patients in whom the CSF drainage results were equivocal, then other factors such as elevated baseline ICP and/or high Rout will also be considered for a shunt under these circumstances

Exclusion Criteria:

• Age < 40
• Fixed musculoskeletal deformities that will exclude gait improvement
• Advanced dementia
• Inability to obtain an MRI study
• General medical conditions in which operative risks are excessive
• Patients taking Warfarin (Coumadin) will be excluded

Hospitalized NPH and non-NPH patients