What is a shunt patency study?
The shunt system is generally composed of a valve that regulates flow of cerebrospinal fluid (CSF), a proximal catheter that drains it from the brain or spinal column to the valve and a distal catheter that drains the CSF from the valve into the abdominal cavity or heart generally. The shunt patency is a study to determine if cerebrospinal fluid (CSF) is actually flowing through the shunt system (valves and proximal and distal catheters). By injecting a small volume (about 0.3 ml) of a radiotracer into the shunt reservoir, the flow of CSF through the catheters and valve can be measured.
How does it differ from a shunt X-ray?
While a shunt X-Ray can tell the settings of the shunt (if programmable) and if there is a physical break in the catheters, it cannot tell if cerebrospinal fluid (CSF) is actually flowing through the shunt system
Why is the test performed?
Your physicians may request this test if, based on your clinical assessment, they suspect that your shunt is no longer working as expected.
What precautions are necessary before a shunt study?
Always let your physicians know if for some reason you are not felling well on the day of the study or suspect you may have an infection. Also inform your physicians about any blood thinners you may be taking. If you have a ventriculo-atrial shunt (shunt that drains into the heart) you may need a single dose of an antibiotic just before the shunt patency study is performed.
How is the test performed?
The patient is positioned lying down under the camera system. The hair around the shunt reservoir is clipped or shaved. The area is cleaned with a sterile solution of Povidone iodine and alcohol. The reservoir is punctured with a tiny needle. A small amount of the patient’s own CSF is aspirated into a syringe. A small amount (0.3ml) of radiotracer is injected through the needle and flushed with the patient’s own CSF. Pictures are taken every minute for 20 minutes to track the flow of the radiotracer through the shunt system. If no flow is observed the patient is asked to sit up and walk around for 5-10 minutes before more pictures are taken. Rarely, delayed pictures after 1-2 hours may be necessary.
How the test will feel?
There will only be slight discomfort when the needle punctures the shunt reservoir. A very small sized needle (25G) is used. You will need to lie down for about 30 minutes in total. You are required to hold the head still when pictures are taken every minute for 20 minutes so it is important to find a comfortable position to lie in before the test starts.
What if it is not successful?
Occasionally, there may be difficulty accessing the shunt reservoir or aspirating CSF from it. In that case alternative tests will need to be done under the guidance of your physician.
What are the risks associated with a shunt patency?
There is a small risk of bleeding, shunt infection and meningitis (<1%). Please let your physician’s know if for any reason you are not feeling well or may have an infection. Also inform them, before the procedure is scheduled, about any blood thinners you may be taking.
What results can one expect from the shunt patency and when?
Analysis of all the pictures and calculations of flow can take up to 24 hours so your physician’s will generally call you with the results the day after the test. The study results cannot be used by themselves to suggest normal or abnormal function. Results from this study have to be interpreted in combination with results from other studies (MRI, CT, lumbar puncture, etc.) and your clinical assessment.