Assessment of ShuntCheck Performance Characteristics in Asymptomatic Patients With Normal Pressure Hydrocephalus

Inclusion Criteria: * Asymptomatic men or women 40 years old or older and have a ventriculoperitoneal shunt placed for normal pressure hydrocephalus and are visiting for routine care. * Capable of providing valid signed informed consent, or has a legal guardian, health care agent, or surrogate decision maker capable of providing valid, signed informed consent. Exclusion Criteria: * Presence of multiple shunts, or presence of more than one distal shunt catheter (regardless of function) crossing the clavicle ipsilateral to the shunt with suspected obstruction; * ShuntCheck test would interfere with standard patient care, or emergency shunt surgery that cannot be delayed is indicated; * Presence of an interfering open wound or edema over any portion of the ventriculoperitoneal shunt.