I. Overview
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| 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.
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
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.
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| 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
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