Hydrocephalus is a neurological condition where an excessive amount of cerebrospinal fluid (CSF) accumulates within the brain’s ventricles. This fluid buildup causes the ventricles to swell, which increases the pressure inside the skull and can compress delicate brain tissue. To manage this dangerous intracranial pressure, neurosurgeons employ methods to divert the extra CSF, with the External Ventricular Drain (EVD) and the Ventriculoperitoneal (VP) Shunt being the two primary surgical interventions. These devices represent distinct approaches to fluid management, one offering immediate, temporary relief and monitoring, and the other providing a long-term, permanent solution.
The EVD: Acute Relief and Monitoring
The External Ventricular Drain (EVD) is a temporary system designed for acute management of elevated intracranial pressure (ICP). It involves placing a thin, soft catheter directly into one of the brain’s ventricles and connecting it to a closed, sterile drainage and collection system outside the body. This system uses gravity to control the flow, with the height of the external collection chamber relative to the patient’s head determining the pressure at which CSF will drain.
The EVD serves a dual purpose: it provides immediate therapeutic drainage of CSF to relieve high pressure, and it acts as a real-time monitor. A transducer connected to the system continuously measures the ICP. This ability to drain fluid and simultaneously monitor pressure is invaluable in unstable patients, such as those with acute hemorrhage, traumatic brain injury, or while treating a CSF infection.
Because the system has a direct opening to the outside environment, it carries an inherent risk of infection, specifically ventriculitis, making it a short-term intervention. The patient’s mobility is severely limited, as the external drain must be meticulously maintained at a specific height and requires strict bedside nursing care.
The VP Shunt: Long-Term CSF Diversion
The Ventriculoperitoneal (VP) Shunt is a device intended for the permanent, long-term management of chronic hydrocephalus. Unlike the EVD, the VP shunt is an entirely internal system consisting of three main parts: a proximal catheter, a valve mechanism, and a distal catheter. The proximal catheter is placed into a brain ventricle, and the entire system is implanted beneath the skin, eliminating any external connection.
The shunt’s valve is its regulating mechanism, controlling the flow of CSF to maintain pressure within a healthy range. This one-way valve opens to drain fluid when the intracranial pressure exceeds the set limit and closes to prevent overdrainage. Many modern shunts use a programmable valve, which allows the surgeon to non-invasively adjust the pressure settings after implantation using an external magnet.
The distal catheter is tunneled under the skin, typically terminating in the peritoneal cavity. The peritoneum is chosen because it has a large surface area and can effectively absorb the diverted CSF back into the bloodstream. This internal design allows the patient to resume normal daily activities.
Clinical Choice and Ongoing Patient Management
The decision between using an EVD and a VP Shunt is based on the patient’s clinical stability, the cause of the hydrocephalus, and the expected duration of treatment. The EVD is reserved for acute, unstable situations or when the CSF is infected, as the presence of bacteria makes implanting permanent hardware too risky. The EVD is typically managed in an intensive care unit (ICU) setting.
The VP Shunt is the definitive treatment for chronic, stable hydrocephalus, where the obstruction or absorption issue is not expected to resolve on its own. While the VP Shunt has a lower initial infection rate than the EVD, its main long-term challenge is mechanical failure, which necessitates surgical revision.
VP shunts can fail due to obstruction from tissue or protein, kinking of the catheter, or valve malfunction, leading to a return of hydrocephalus symptoms. Pediatric patients face a high lifetime revision risk. The internal nature of the VP shunt allows for patient mobility and discharge from the hospital, but it requires periodic long-term monitoring for signs of underdrainage or overdrainage. Overdrainage can cause the ventricles to collapse and may lead to headaches or hemorrhage, while underdrainage results in a recurrence of symptoms as pressure rises.