Complications and malfunctions of shunt systems

Sadly, much of my inspiration for blogs on hydrocephalus come about because of a bad situation that occurs either to me or one of my friends with hydrocephalus. This is one of those occasions. Early Monday morning, one of my friends passed away after tubing from his shunt broke and came into contact with his brain stem. You might wonder how such a thing could happen. So named because of its stem-like appearance, the brain stem is where the base of the brain attaches to the spinal cord. (WebMD, 2016) it's main job is to control the flow of messages between the brain and the rest of the body; it is also controls basic body functions such as breathing, heart rate, and blood pressure.

What can go wrong?

Hydrocephalus is treated by surgically implanting a shunt into the patient's brain, however, complications can develop or the shunt can malfunction. Interestingly, in pediatric patients, there is a fifty percent (50%) shunt failure rate after only two (2) years. The exact cause for this is unclear.

Shunt malfunction

A partial or complete blockage of the shunt system is know as a shunt malfunction. (Hydrocephalus Association, 2014) When this occurs, cerebrospinal fluid builds up and causes symptoms similar to those seen with untreated hydrocephalus.

The blockage is caused by a build-up of blood cells, tissue, or bacteria and occur anywhere system. Both the proximal catheter (which is implanted in the brain) as well as the distal catheter (which can be implanted either in the ventricle of the heart, the peritoneal cavity of the abdomen, or, rarely, in the spine) can be blocked. These blockages originate in either the choroid plexus or the ventricles of the brain. Generally speaking, in adult hydrocephalus patient's, blockages occur with greater frequency in the distal catheter.

Generally, a shunt system is durable, however, components of the system (pictured below) can become disengaged or fractured as the result of normal wear -- particularly in children due to their growth spurts. Also, although rare, a valve can fail due to a mechanical malfunction.

Shunt infection

A shunt infection usually occurs as a result of the person's own bacterial organisms and isn't caused by be exposed to someone who is sick. The most common bacterium to cause an infection is Staphlococcus epidermis. which is normally present on a person's skin as well as in the hair follicles and in the sweat glands. This type of infection is typically seen one (1) to three (3) months after shunt implant surgery, but can occur up to six (6) months later. In persons with a ventriculoperitoneal (VP) shunt is a shunt infection that occurs secondarily to an abdominal infection. Lastly, in persons treated with a ventriculoatrial shunt (which empties into the right ventricle of the heart) a generalized infection can occur.

Other shunt complications

Over drainage causes the ventricles to decrease in size and become slit-like (see: What is slit ventricle syndrome (SVS)?) due to the brain and meninges pulling away from the skull. SVS is most common in young adults who have been shunted since early childhood. A telltale symptom of SVS is severe intermittent headache that improves when the person is laying down.

Under drainage does the exact opposite and causes the ventricles to swell. When this occurs, the shunt might not be able to relieve the hydrocephalus symptoms. In order to restore a balanced flow of CSF, it might be necessary to implant a new shunt with a more accurate pressure valve. If the person has a shunt with programmable valves, the balance of flow can be restored by resetting the opening pressure.

 Subdural hematoma (pictured at left) occurs when a broken blood vessel in the meninges becomes trapped between the skull and the brain. It is seen most commonly in adults with Normal pressure hydrocephalus (NPH) and requires surgical intervention to correct it.

Multiloculated hydrocephalus is located (isolated) CSF compartment in the ventricular system that is enlarged and not in communication with the normal ventricle. It can be the result of trauma at birth, neonatal intraventricular hemorrhage, Ventriculitis, over drainage, or other conditions. This complication might be difficult to identify because it is typically seen in infants and children who might be neurologically compromised. Treatment involves surgery to implant ventricular catheters, Craniotomy and fenestration (opening) of the intraventricular loculations. (John Hopkins Medical, N.D.)

Seizures can sometimes occur in people (both adults and children) with hydrocephalus. Medical research has shown there is NO CORRELATION (emphasis added) between the site a shunt implant (or the number of revisions a person has) and a increased risk of developing seizures. The one possible exception to this involves children who have significant cognitive delays or motor disabilities are at higher risk (italic emphasis added) are more likely to experience seizures compared to children without similar delays or disabilities. Research has also shown that seizures aren't likely to occur at the time a shunt malfunctions, and the more likely explanation for the occurrence of a seizure disorder is related to an associated malformation of the cerebral cortex.

Abdominal complications can also occur in patient's with hydrocephalus who are treated with a shunt. This is due to the fact the distal catheter of a ventriculoperitoneal (VP) shunt is placed in  the peritoneal cavity of the abdomen. Although complications associated with a VP shunt aren't less in frequency (when compared to a ventriculoatrial [VA] shunt), they tend to be less severe and have a lower mortality rate. These complications can include: peritoneal pseudocysts, loss of the distal catheter, bowel perforations, and hernias.

When shunts go bad: complications experienced with shunt systems

X-ray images of a 20-month old hydrocephalus patient
experiencing shunt malfunction. As a result, the child
experienced sutural diastasis.

Hydrocephalus can be treated with a shunt system, however, this treatment often results in complications. Research has shown that an estimated fifty percent (50%) of shunts in pediatric patients fail within two (2) years often requiring repeated neurosurgery. The most commonly seen of these complications are: infection and malfunction (emphasis added).

I. Common complications

Shunt malfunction

A shunt malfunction involves either a partial or complete blockage (of the tubing) causing the shunt to function intermittently or not at all. As a result of the blockage cerebrospinal fluid (CF) accumulates and, as illustrated in the image at right, can result in diastasis where a fracture line traverses one (or more) sutures of the skull resulting in a widening of the suture.

The blockage can result from blood cells, tissue, or bacteria and occur in any part of the shunt. Both the ventricular catheter (the portion of the system placed in the brain) and the distal catheter (the portion of the system that drains CSF to other part of the body) can become blocked by tissue from the choroid plexus (which produces CSF) or ventricles. In adults, the blockage occurs most commonly in the distal portion of the shunt system.

Shunts - by their very nature - are very durable, but their components can become disengaged or fractured as a result of wear or as a child grows. In rare cases valve failure can occur due to a mechanical malfunction.

Shunt infection

Typically a shunt infection occurs because of the person's own bacteria and isn't acquired from someone else who is ill. The most common infection to occur in a shunt system is Staphylococcus Epidermidis which is know for attacking indwelling medical devices such as a shunt. which is normally found both on the surface of a person's skin as well as in the sweat glands. Normally a shunt infection occurs with a one (1) to three (3) month window following shunt implant surgery, but has been known to occur up to six (6) months following the surgery. Research has shown that patients receiving a ventriculoperitoneal (VP) shunt are statistically at the highest risk for developing a shunt infection secondary to abdominal infection.

II. Less common complications

Over drainage

CT scan shows hydroceplaus
patient with SVS.

This complication causes ventricles to decrease in size causing slit-like ventricles due to the brain and its meninges pulling away from the skull. Known as slit-ventricle syndrome or SVS for short (pictured at right) , it is most commonly seen in young adults (ages 20 - 39) who were shunted as a child. One symptom that is unique to SVS is the severe intermittent headache that can be relieved by lying down. In order to confirm a diagnosis of SVS, imaging must be completed that shows the smaller size ventricles.

Under drainage

Results in the exact opposite problem as over drainage and that is an increase in the size of ventricles as well as the inability to relieve the symptoms associated with the hydrocephalus. In some cases, to restore a balanced flow of CSF, it might be necessary to implant a new shunt with a more accurate pressure valve. In patient's with a programmable shunt, it is possible to restore a balanced flow by simply re-setting the opening pressure.

Subdural hematoma

Control unit of a programmable shunt.

This is generally seen in older adults (ages 60 - 80) and is caused when blood from a broken vessel in the meninges becomes trapped between the skull and the brain. Surgical intervention is required to correct this complication.

Multiloculated hydrocephalus

This condition occurs when a located (isolated) compartment in the ventricular system becomes enlarged and not in communication with the normal ventricle. There a numerous documented causes including: neonatal intraventricular hemorrhage, trauma that occurs at birth, ventriculitis (inflammation of the ventricles), or shunt-related infection. Typically it can be difficult to identify due to the fact that it is most often seen in infants and children who might be neurologically compromised.

 
For additional information: Complications of shunt systems

Shunting as a means to manage hydrocephalus

I. Overview

Subarachnoid spaces in the brain

I. Overview

Over the years, the management of hydrocephalus has challenged neurologist, engineers, and medical device manufacturer alike due to the unique nature of cerebrospinal fluid (CSF) dynamics in each person. Known as a "CSF diversion device", a shunt has become the primary therapy used in hydrocephalus management for over sixty (60) years. The shunt, which is surgically implanted within a ventricle in the patient's brain (or in the subarachnoid spaces around the brain), works by diverting the CSF to another part of the body where it is absorbed. This creation of an alternate pathway typically restores the physiological balance between CSF production, flow, and absorption when one or more of these functions has been impaired. Once it has been inserted, valves within the shunt's pathway act like on/off switches, opening when the differential pressure, that is, the pressure difference across the valve, exceeds the valve's opening pressure.

Blog author Walter Little with his
grandparents, James and Sara Sanders,
and Officer Dorsey Goss (1973)

II. What are the complications of shunting?

As I alluded to above, a shunt provides an alternate pathway through which CSF can bypass obstruction(s) in the fluid compartments (ventricles) of the brain. Such a bypass relieves the excess fluid backup the causes hydrocephalus. When both the CSF production and absorption are in balance, the hydrocephalus is considered to be "compensated". In contrast, when production exceeds aborption, complications such as elevated pressure or overdrainage occur and can mimic a malfunctioning shunt.

More detailed information can be found on the Hydrocephalus Association website, but here is a brief overview of some of the most common complications:

Malfunction

As is the case with any piece of equipment, a shunt might break. Additional they are subject to becoming disconnected, migrating (moving), or, most commonly, becoming blocked. (It should be noted that the disconnection and migration are particularly prevalent in children with a shunt due to the child's growth.)

Infection

Shunts can become colonized with bacteria or - in rare instances - fungi which typically occurs at the time the shunt is implanted. In an effort to combat this, some manufacturers have began to add anti-microbial coating to their shunts which appears to be reducing the rate of post-surgical infection.

Material degradation

Originally, barium sulfate (BaSO4) was mixed with silicone to allow the shunt catheter to be visible on an x-ray. These would eventually dissolve making the tubing surface rough. When tissue in-growth occurred to the tubing, it would bind at that location resulting in deterioration and/or breakage. Over time the design of shunt tubing has changed and a clear silicone elastomer now covers the surface of the tubing greatly decreasing the likelihood of degradation.

 Shunt revision(s)

I put an "s" on revision because the average person with hydrocephalus undergoes 2.66 shunt revisions over the course of their lifetime. These can be required at any time to correct one (or more) of the complications outlined above or to compensate for growth in the case of children and young adults. If a blockage is suspected, it must be confirmed by a neurosurgeon who evaluates the implanted system to determine whether the problem is the result of a complete or partial blockage, if a disconnection has occurred, or whether the current system just can't no longer meet the needs of the individual.

Additional information:

Shunt system fact sheet