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