The brain and spinal cord are surrounded by a clear liquid called cerebrospinal fluid (CSF), which serves to cushion these delicate structures, deliver nutrients, and remove waste products. The body continuously produces and reabsorbs CSF in a balanced cycle. However, sometimes this balance is disrupted, leading to an abnormal accumulation of CSF within the brain’s hollow cavities, known as ventricles. This condition, called hydrocephalus, causes the ventricles to enlarge and increases pressure inside the skull, potentially leading to various neurological issues if not managed. Medical interventions are often necessary to drain this excess fluid and relieve the pressure.
External Ventricular Drains
An External Ventricular Drain (EVD) is a temporary medical device used to drain excess cerebrospinal fluid (CSF) directly from the brain’s ventricles. It is employed in acute situations where there is a sudden buildup of fluid or blood within the brain, leading to increased intracranial pressure (ICP). The EVD system works by diverting CSF from the ventricles to an external collection bag.
The EVD system consists of a thin, flexible catheter, which is inserted through a small hole in the skull, usually into one of the brain’s lateral ventricles. This catheter connects to an external drainage system that includes tubing, a drip chamber, and a collection bag. Drainage is regulated by gravity; the height of the collection system relative to the patient’s head determines the amount of CSF that drains.
EVDs are for short-term management in emergency or critical care settings. They reduce pressure inside the brain caused by temporary blockages or abnormal CSF flow, or divert infected CSF while antibiotics are administered. EVDs also allow for continuous monitoring of intracranial pressure, providing real-time data to guide treatment. EVDs are temporary, typically remaining in place for several days to a week or longer.
Ventriculoperitoneal Shunts
A Ventriculoperitoneal (VP) shunt is a permanent, internal medical device designed to manage chronic hydrocephalus by diverting excess cerebrospinal fluid (CSF) from the brain. It remains inside the body, providing a long-term solution for fluid drainage. This device helps maintain stable intracranial pressure by rerouting CSF to another part of the body where it can be naturally absorbed.
The VP shunt system is composed of three main parts: a ventricular catheter, a valve, and a peritoneal catheter. The ventricular catheter is a thin, flexible tube that a neurosurgeon places into one of the brain’s ventricles to collect excess CSF. The valve, which is typically placed under the skin behind the ear or on the top of the head, regulates the flow of CSF and prevents backflow. Some valves are programmable, allowing doctors to adjust the drainage settings externally after implantation.
The peritoneal catheter is a longer tube connected to the valve. This catheter is tunneled under the skin, down the neck, and into the abdominal cavity, specifically the peritoneum. The peritoneum is a membrane lining the abdominal organs that can readily absorb the excess CSF into the bloodstream. Once connected, the VP shunt drains CSF, alleviating pressure on the brain and helping to ease hydrocephalus symptoms. This system allows patients to resume normal activities.
Primary Distinctions and Clinical Application
The fundamental difference between External Ventricular Drains (EVDs) and Ventriculoperitoneal (VP) shunts lies in their duration of use and drainage mechanism. An EVD drains CSF to a collection bag outside the body, requiring the patient to be largely immobile and under constant medical supervision. A VP shunt, in contrast, diverts CSF internally to the abdominal cavity, allowing patients to live a more normal and active life once recovered from the surgery.
Clinical scenarios dictate the choice between these two devices. EVDs are used for acute management of hydrocephalus, often in emergencies following conditions like traumatic brain injury or hemorrhage. They are also employed to treat infections by draining infected CSF or to serve as a temporary measure while a patient stabilizes before a permanent solution can be considered.
VP shunts are the preferred treatment for chronic hydrocephalus, including congenital hydrocephalus, normal pressure hydrocephalus, or cases where acute hydrocephalus resolves but a permanent drainage issue remains. This includes situations where an EVD has successfully managed an acute episode, but the patient cannot reabsorb CSF, necessitating conversion to a permanent shunt. The decision to use one over the other is based on the immediate medical need, the underlying cause of the hydrocephalus, and the long-term prognosis for CSF absorption.