A shunt is a medical device designed to manage hydrocephalus, a condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within the brain’s ventricles. This excess fluid increases pressure inside the skull, which can damage brain tissue. The shunt system works by diverting the excess CSF away from the brain to another part of the body, such as the abdominal cavity, where it is safely absorbed into the bloodstream. A shunt malfunction, or shunt failure, occurs when this system stops working effectively, failing to drain or properly regulate the flow of CSF. This leads to a recurrence of the symptoms the shunt was meant to prevent.
What Shunts Do and How They Fail
A typical ventriculoperitoneal (VP) shunt consists of three main components: a catheter placed in the brain’s ventricle, a valve mechanism, and a distal catheter that drains the fluid into the abdominal space. The valve is a pressure-regulating component that ensures the CSF drains at an appropriate rate, preventing both excessive and insufficient fluid removal. This system is surgically implanted entirely beneath the skin and is often needed for the patient’s lifetime.
Failure of this device is generally categorized into two mechanical issues: obstruction or mechanical breakdown. Obstruction involves a blockage that prevents the CSF from flowing through the system, causing pressure to build up again in the brain. Mechanical breakdown refers to the physical failure of the components, such as a disconnection or fracture of the tubing.
The Primary Causes of Failure
Obstruction is the most common reason for shunt failure. Blockages can occur at the proximal end, where the catheter sits in the ventricle, often due to brain tissue, cellular debris, or the choroid plexus growing into the catheter opening. Distal obstruction is also common and happens at the drainage site, such as the peritoneal cavity, where the catheter can become clogged by tissue or debris.
Infection represents another significant cause of malfunction, particularly within the first few months after implantation. These infections are typically bacterial, often caused by the patient’s own skin flora, which can colonize the shunt material. An infection causes inflammation that can lead to internal blockages and requires prompt treatment. This usually involves the temporary removal of the entire shunt system and a course of antibiotics.
Mechanical integrity can be compromised through disconnection, fracture, or migration of the tubing or valve. Fractures can occur due to wear and tear or physical stress, sometimes near bony structures. In growing children, the catheter may become too short relative to the child’s height, leading to displacement or kinking that disrupts the fluid path.
Shunt valves can also malfunction, leading to problems with the rate of drainage rather than a complete blockage. Over-draining occurs when the valve allows CSF to exit the ventricles too quickly. This can cause the brain to pull away from the skull, potentially leading to the tearing of blood vessels and forming a subdural hematoma. Conversely, under-draining means the valve is removing fluid too slowly, allowing the high pressure to return and the original symptoms of hydrocephalus to recur.
Recognizing the Signs of Trouble
The symptoms of a shunt malfunction are a direct result of the returning increase in intracranial pressure (ICP). These signs often mirror the original symptoms of hydrocephalus, but the clinical presentation varies significantly based on age due to differences in skull structure.
In infants and very young children whose skull bones have not yet fused, the most noticeable signs relate to the expansion of the head. Parents may observe a rapid increase in head circumference or a bulging and tense fontanelle. Other common symptoms include persistent vomiting, excessive sleepiness (lethargy), increased irritability or fussiness, and “sun-setting eyes,” where the eyes deviate downward.
For older children and adults, whose skulls are fully fused, the increase in ICP manifests as severe, persistent headaches. These headaches are often worse upon waking because CSF naturally builds up while lying down. Nausea and vomiting without an apparent gastrointestinal cause are frequent complaints.
Behavioral and neurological changes are also indicators of malfunction in older patients. These include:
- Confusion
- Difficulty concentrating
- A decline in academic or job performance
- Changes in personality or mood
- Vision problems, such as blurred or double vision
Any of these symptoms require immediate medical assessment.
Diagnosis and Required Medical Action
When a shunt malfunction is suspected based on clinical symptoms, medical professionals begin with a thorough physical and neurological assessment. This initial check evaluates the patient’s state of consciousness, eye movements, and general responsiveness, which helps gauge the severity of the ICP increase. The next step is to confirm the diagnosis using imaging studies.
A computed tomography (CT) scan or magnetic resonance imaging (MRI) is used to visualize the brain’s ventricles. By comparing the current image to previous scans, doctors look for an increase in ventricular size, which indicates fluid accumulation and confirms a blockage. A shunt series, a set of X-rays taken of the entire shunt tract, is also performed to check for mechanical issues like tubing disconnection, fracture, or displacement.
If a malfunction is confirmed, surgical revision is almost always required. Depending on the location and cause of the failure, the neurosurgeon will replace the affected part of the system—the proximal catheter, the valve, or the distal catheter—or, in some cases, the entire shunt. If the malfunction is caused by an infection, the entire shunt is typically removed temporarily, an external drain is placed, and the patient is treated with antibiotics before a new, sterile shunt is implanted.