The Problem:
Hydrocephalus is the build up of cerebrospinal fluid (CSF) in the cranial cavity and ventricles. It occurs in 1 to 2 of every 1000 births, making hydrocephalus as prevalent as Down’s Syndrome. The build up of CSF leads to possibly fatal levels of intracranial pressure (ICP). To alleviate remedy hydrocephalus, neurosurgeons implant patients with a ventriculoperitoneal (VP) shunt system. The shunt system utilizes two catheters, each connected to one end of a pressure gated reservoir valve, to route CSF away from the head, and into the peritoneal cavity for re-absorption.
Ventriculoperitoneal shunts work very well at ameliorating the symptoms of hydrocephalus, however most shunts will fail at some point in their lifetime. Furthermore, 13.3 % of shunts fail within the first 30 days of implantation. When this near inevitable failure occurs, a surgery is required to fix or replace the shunt system. However shunt malfunction is not an easily predictable phenomenon. There are no clear cut symptoms of a failed shunt. Some patients and physicians report occasional flu like symptoms (e.g. headache, vomiting, dizziness, etc.), but these are not reliable.
The only reliable methodology for detecting shunt failure is to perform an invasive surgery. These surgeries not only expose patients to the risk of infection, hemorrhage, or other surgical complications, but are also quite costly. On average, a shunt surgery costs the patient around $35,000. Each of these factors leads to a palpable clinical need for a noninvasive methodology to detect a failed shunt system.
Current Solutions:
As previously mentioned, the only surefire way to detect shunt failure is an invasive surgery. Currently, only one noninvasive methodology exists – the ShuntCheck device by NeuroDx. ShuntCheck utilizes a thermodilution technique to detect flow in a shunt system. However, literature has shown that flow detection via ShuntCheck is not indicative of shunt function. This could be resultant from the inherent intermittent flow in shunt systems, or thermal dilution’s natural ability to diffuse regardless of the presence of flow.
Other techniques include the injection of a radioactive isotope for detection using an x-ray, and some instances of using Magnetic Resonance Imaging (MRI). However x-ray techniques introduce dangerous radioactive materials to the patient and can become expensive. Additionally, MRI is time consuming, costly, and requires the patient to sit still for a long period of time, which can become difficult for small children with a failing shunt.
Our Methodology:
We demonstrated that we can monitor the behavior of the shunt’s silicon membrane valve in order to diagnose if the shunt is functioning properly, or if there is a blockage in one of the catheters. Here is a short video of our experimental design composed of: a variable pressure pump (to mimic pulsatile CSF flow from the ventricles), catheters leading into and away from the shunt reservoir, a piece of SynDaver synthetic skin, and the ultrasound transducer and system:
And here is a video of what it looks like when we track the valve’s velocity over time. In this video, you see that the B-mode image on the left (a two dimensional image generated from the ultrasound data) shows the silicon membranve valve, and on the right is a real-time plot of the valve’s velocity. For the first 6 seconds, fluid is flowing normally through the valve. At approximately 6 seconds, we induce a blockage in the proximal (ventricular) catheter and note that the valve stops moving in the B-mode image, and the velocities are immediately quieted. Around 10 seconds, we release the blockage, and valve motion begins again.
Going Forward:
Even though the year is over, we’re not done with shunts! We are currently working on implementing our methodology in an easy to use, disposable device. Check the Prototype tab later to see what we make!
Don’t like our descriptions? Want to find out more? Here are some links!
Wikipedia: