Definition & Overview
A ventriculoperitoneal shunt (VP shunt) is a device that is primarily used in the treatment of hydrocephalus, a medical condition characterised by the excessive buildup of cerebrospinal fluid (CSF) in the brain. A VP shunt is designed to drain the fluid from the brain to another part of the body, such as the peritoneal cavity (abdominal area).
VP shunts are highly effective. However, they can malfunction or become blocked. One way to fix such problems is puncturing the shunt tubing or reservoir, a procedure referred to as VP shunt tap. This involves obtaining CSF from the shunt tubing or reservoir for further analysis to determine the cause of a malfunctioning VP shunt.
There are two basic types of VP shunts: fixed and programmable. Fixed shunts are usually used in infants and newborns. With this shunt, the amount of fluid drained through the device remains constant. Meanwhile, programmable shunts, as the name suggests, can be programmed to drain different amounts of fluid at certain times or when required.
VP shunts are complicated mechanical devices and are typically consist of three major components:
- Inflow catheter, which is placed near the area of blockage in the brain’s ventricle (the part of the brain where CSF accumulates)
- Valve, which controls the flow of fluid through the device
- Outflow catheter, a tube that connects to the peritoneal cavity
Some shunts also contain a reservoir where CSF is collected. Should there be any concerns on the performance of the shunt, a CSF sample is obtained from the reservoir for testing. Should doctors also need to introduce medications, they can do so by injecting the medication into the reservoir or chamber.
Who Should Undergo & Expected Results
As mentioned earlier, VP shunts are used in patients with hydrocephalus.
Hydrocephalus is a condition wherein CSF fluid builds up in the brain instead of being reabsorbed by the body. The brain naturally produces almost half a litre of CSF daily. The fluid helps carry important minerals throughout the brain and helps protect the organ and the spinal column from injuries.
People with hydrocephalus are unable to excrete CSF due to a blockage, or their brains are overproducing the fluid. When this happens, the skull enlarges due to excessive amounts of CSF, especially in infants.
It is important to understand that there is no cure for hydrocephalus. People with the condition will usually have it for the rest of their lives. In some cases, the cause of the blockage can be removed surgically to allow the normal flow of CSF, but for most people, this is not a possibility. A VP shunt can help people suffering from hydrocephalus live a normal life. However, they will also be living the rest of their lives with the shunt in their brains. Since shunts are mechanical devices that rely on the proper flow of fluids, they are prone to malfunctions caused mainly by blockages. When this occurs, surgeons will have to perform a VP shunt tap to determine the exact cause.
How is the Procedure Performed?
A VP shunt tap is a relatively simple and quick procedure. In most cases, it is performed following a consultation with a neurosurgeon. However, if the patient displays symptoms that indicate an emergency, the procedure may be performed right away without prior consultation.
Before the procedure, the patient, parents, or guardians are informed of the process, what to expect, and why it is being performed. After obtaining consent, the doctor will review previous imaging information to identify the exact location of the reservoir, chamber, or tubing.
After locating the reservoir, the doctor will clean the area with an antiseptic. In most cases, hair covering the area will simply be parted. The area will only be shaved if absolutely necessary.
The doctor will then insert a needle and guide it to the reservoir. CSF will flow through the needle into a tube and container where it is collected. Around 5ml of CSF is collected for each tube. Once a sufficient amount of CSF has been collected, the needle is removed and slight pressure is applied to the entry site to close the small puncture wound.
The collected CSF will then be forwarded to a laboratory where it is analysed. The lab will analyse the cell count, glucose level, culture, gram stain, and protein level of the obtained sample.
Possible Risks and Complications
A VP shunt tap is a relatively simple procedure, but it still has associated risks and possibility of complications.
It is important that the doctor performing the tap is familiar with the type of shunt that the patient has to avoid puncturing the wrong tube or missing the reservoir. If this happens, not only would the tap create more problems, but an intracranial haemorrhage can also occur.
Complications of shunt tap include bleeding, infection, and CSF leak from the entry site. Ventricle collapse is also possible and this can further block the shunt.
Pinto FC, Saad F, Oliveira MF, Pereira RM, Miranda FL, Tornai JB, et al. Role of endoscopic third ventriculostomy and ventriculoperitoneal shunt in idiopathic normal pressure hydrocephalus: preliminary results of a randomized clinical trial. Neurosurgery. 2013 May. 72 (5):845-53; discussion 853-4.
Spiegelman L, Asija R, Da Silva SL, Krieger MD, McComb JG. What is the risk of infecting a cerebrospinal fluid-diverting shunt with percutaneous tapping?. J Neurosurg Pediatr. 2014 Oct. 14 (4):336-9.