A shunt is a small, flexible medical device designed to relieve pressure that builds up inside the brain. This device functions as a drainage system, redirecting excess fluid from the brain to another part of the body where it can be safely absorbed into the bloodstream. The shunt is a common treatment for hydrocephalus, which translates from Greek to “water on the brain”. The shunt provides a mechanical solution to a fluid imbalance, allowing the brain to function without the damaging effects of high pressure. This implantable system is a long-term solution that requires ongoing monitoring.
Understanding Hydrocephalus
Hydrocephalus is characterized by the abnormal accumulation of cerebrospinal fluid (CSF) in the brain’s ventricles, the fluid-filled cavities deep within the brain. The body constantly produces CSF, a clear, colorless fluid that cushions the brain and spinal cord, delivers nutrients, and removes waste. In a healthy person, CSF circulates through the ventricles before being reabsorbed into the bloodstream.
This natural cycle of production, circulation, and absorption is disrupted, leading to an imbalance. This disruption is most often caused by an obstruction that blocks the flow of CSF, or less commonly, by reduced absorption or overproduction. When the fluid builds up, the ventricles expand, putting harmful pressure on the surrounding brain tissue. This elevated intracranial pressure can lead to symptoms like headaches, vomiting, and vision problems, and can cause permanent brain damage if untreated. The condition can be present at birth or acquired later in life due to injury, infection, or tumors.
Anatomy and Function of a Hydrocephalus Shunt
The hydrocephalus shunt is a system made up of three primary components working together to manage fluid pressure. The first is the proximal catheter, a flexible tube placed inside one of the brain’s ventricles. This catheter serves as the inlet, drawing excess cerebrospinal fluid (CSF) away from the brain tissue.
The proximal catheter connects to the second component: the one-way valve mechanism. This specialized valve is typically placed beneath the skin, often behind the ear or on the top of the head. The valve regulates CSF flow and maintains a specific intracranial pressure, remaining closed until the fluid pressure exceeds a predetermined setting.
Once the pressure threshold is crossed, the valve opens, allowing the excess fluid to drain. When the pressure drops to a safe level, the valve closes, preventing overdrainage. The third component is the distal catheter, a long tube tunneled under the skin to a different area of the body, where the redirected CSF is naturally absorbed.
Common Shunt Systems and Surgical Placement
Shunt systems are classified by the destination where the CSF is diverted. The two most common types are the Ventriculoperitoneal (VP) and the Ventriculoatrial (VA) shunts. The VP shunt is the most frequently used, draining fluid from the brain’s ventricles to the peritoneal cavity, the space within the abdomen, which efficiently absorbs the excess CSF.
The VA shunt directs the CSF from the ventricles into a chamber of the heart, the atrium. A less common option is the Lumboperitoneal (LP) shunt, which drains fluid from the lower spine to the abdominal cavity. A neurosurgeon selects the appropriate system based on the patient’s age, the cause of hydrocephalus, and other medical factors.
Valves come in various designs, including fixed-pressure and adjustable (programmable) valves. Fixed-pressure valves regulate CSF flow based on a single setting established before surgery. Programmable valves allow a clinician to non-invasively change the pressure setting after implantation using a magnetic tool. This adjustability is beneficial because a patient’s pressure needs may change over time, allowing drainage to be fine-tuned without additional surgery. Surgical placement involves inserting the proximal catheter and valve through a small scalp incision, then tunneling the distal catheter under the skin to the chosen drainage site.
Long-Term Management and Warning Signs
The implanted shunt system requires continuous monitoring. The two main types of long-term complications are malfunction and infection, both of which can cause the symptoms of hydrocephalus to return. A shunt malfunction occurs when the system becomes blocked, broken, or displaced, or when the valve setting is incorrect, leading to under- or overdrainage. Blockage is often caused by tissue or protein buildup within the catheter and requires emergency medical attention.
Infection is another risk, most commonly occurring within the first few months after the initial surgery. Signs of a shunt infection can include fever, redness, and tenderness along the path of the shunt, or neck stiffness. Recognizing the warning signs of a malfunction is important, as symptoms often mirror the original signs of high intracranial pressure.
Common signs in older children and adults include:
- Severe headache.
- Nausea.
- Persistent vomiting.
- Excessive sleepiness.
- Changes in vision, such as double or blurred sight.
In infants, warning signs can include an unusually large or rapidly growing head, a bulging soft spot (fontanelle), or downward deviation of the eyes. Any suspicion of shunt failure or infection necessitates immediate contact with a medical professional.