This study evaluates the performance of a thermal anisotropy measurement device for non-invasively assessing CSF shunt flow. Patients with an existing implanted shunt and symptoms of shunt malfunction who require shunt revision surgery will be evaluated with the study device to assess flow in CSF shunts as confirmed by surgical outcomes at 7 days. If successful, this study will show that the study device accurately distinguishes between functioning (flowing) and non-functioning (non-flowing) shunts.

Inclusion Criteria:

1. Existing ventriculoperitoneal CSF shunt on which the subject is dependent
2. At least one symptom of shunt malfunction as determined by the investigator, such as but not limited to seizure, fever, headache, vision problems, dizziness, disorientation, confusion, vomiting, lethargy, irritability, difficulty waking or staying awake, swelling along shunt tract, enlargement of head, loss of balance, gait disturbance, and loss of sensory or motor function
3. Exhibit shunt malfunction symptom(s) requiring surgical shunt revision per standard of care assessment without use of device data
4. Region of intact skin overlying an unambiguously identifiable chronically indwelling ventricular shunt which crosses the clavicle and is appropriate in size for application of the study device
5. Available for follow-up for up to seven days
6. Signed informed consent by subject or a parent, legal guardian, health care agent, or surrogate decision maker (according to local statutes, and collectively referred to as "surrogates" in this protocol)

Exclusion Criteria:

1. Presence of more than one distal shunt catheter in the study device measurement region
2. Presence of an interfering open wound or edema in the study device measurement area
3. Subject-reported history of adverse skin reactions to adhesives
4. Investigator judges that the subject is likely to be lost to follow-up due to unavailability or clinical outcome being unobtainable
5. Participation in the study will interfere with, or be detrimental to, administration of optimal health-care to the subject
6. Previous participation in a Rhaeos clinical study in which FlowSense device measurement data were acquired
7. Participation in any other investigational procedural, pharmaceutical, and/or device study that may influence the collection of valid data under this study

Pediatric and adult shunt-dependent hydrocephalus patients with an existing ventriculoperitoneal (VP) shunt who are experiencing shunt malfunction symptoms and require shunt revision surgery per standard of care shunt evaluation without use of the study device data will be enrolled in this study.