A ventricular shunt is a tube that is surgically placed in one of the fluid-filled chambers inside the brain (ventricles). The fluid around the brain and the spinal column is called cerebrospinal fluid (CSF). When infection or disease causes an excess of CSF in the ventricles, the shunt is placed to drain it and thereby relieve excess pressure.
A ventricular shunt relieves hydrocephalus, a condition in which there is an increased volume of CSF within the ventricles. In hydrocephalus, pressure from the CSF usually increases. It may be caused by a tumor of the brain or of the membranes covering the brain (meninges), infection of or bleeding into the CSF, or inborn malformations of the brain. Symptoms of hydrocephalus may include headache, personality disturbances and loss of intellectual abilities (dementia), problems in walking, irritability, vomiting, abnormal eye movements, or a low level of consciousness.
Normal pressure hydrocephalus (a condition in which the volume of CSF increases without an increase in pressure) is associated with progressive dementia, problems walking, and loss of bladder control (urinary incontinence). Even though CSF is not thought to be under increased pressure in this condition, it may also be treated by ventricular shunting.
The congenital form of hydrocephalus is believed to occur at an incidence of approximately one to four out of every 1,000 births. The incidence of acquired hydrocephalus is not exactly known. The peak ages for the development of hydrocephalus are in infancy, between four and eight years, and in early adulthood. Normal pressure hydrocephalus generally occurs in patients over the age of 60.
The ventricular shunt tube is placed to drain fluid from the ventricular system in the brain to the cavity of the abdomen or to the large vein in the neck (jugular vein). Therefore, surgical procedures must be done both in the brain and at the drainage site. The tubing contains valves to ensure that fluid can only flow out of the brain and not back into it. The valve can be set at a desired pressure to allow CSF to escape whenever the pressure level is exceeded.
A small reservoir may be attached to the tubing and placed under the scalp. This reservoir allows samples of CSF to be removed with a syringe to check the pressure. Fluid from the reservoir can also be examined for bacteria, cancer cells, blood, or protein, depending on the cause of hydrocephalus. The reservoir may also be used to inject antibiotics for CSF infection or chemotherapy medication for meningeal tumors.
The diagnosis of hydrocephalus should be confirmed by diagnostic imaging techniques, such as computed tomography scan (CT scan) or magnetic resonance imaging (MRI), before the shunting procedure is performed. These techniques will also show any associated brain abnormalities. CSF should be examined if infection or tumor of the meninges is suspected. Patients with dementia or mental retardation should undergo neuropsychological testing to establish a baseline psychological profile before the shunting procedure.
As with any surgical procedure, the surgeon must know about any medications or health problems that may increase the patient's risk. Because infections are both common and serious, antibiotics are often given before and after surgery.
To avoid infections at the shunt site, the area should be kept clean. CSF should be checked periodically by the doctor to be sure there is no infection or bleeding into the shunt. CSF pressure should be checked to be sure the shunt is operating properly. The eyes should be examined regularly because shunt failure may damage the nerve to the eyes (optic nerve). If not treated promptly, damage to the optic nerve causes irreversible loss of vision.
Serious and long-term complications of ventricular shunting are bleeding under the outermost covering of the brain (subdural hematoma), infection, stroke, and shunt failure. When a shunt drains to the abdomen (ventriculoperitoneal shunt), fluid may accumulate in the abdomen or abdominal organs may be injured. If CSF pressure is lowered too much, patients may have severe headaches, often with nausea and vomiting, whenever they sit up or stand.
After shunting, the ventricles get smaller within three or four days. This shrinkage occurs even when hydrocephalus has been present for a year or more. Clinically detectable signs of improvement occur within a few weeks. The cause of hydrocephalus, duration of hydrocephalus before shunting, and associated brain abnormalities affect the outcome.
Of patients with normal pressure hydrocephalus who are treated with shunting, 25–80% experience long-term improvement. Normal pressure hydrocephalus is more likely to improve when it is caused by infection of or bleeding into the CSF than when it occurs without an underlying cause.
Complications of shunting occur in 30% of cases, but only 5% are serious. Infections occur in 5–10% of patients, and as many as 80% of shunts develop a mechanical problem at some point and need to be replaced.
In some cases of hydrocephalus, certain drugs may be administered to temporarily decrease the amount of CSF until surgery can be performed. In patients with hydrocephalus caused by a tumor, removal of the tumor often cures the buildup of CSF. Approximately 25% of patients respond to therapies other than shunt placement.
Patients with normal pressure hydrocephalus may experience a temporary improvement in walking and mental abilities upon the temporary drainage of a moderate amount of CSF. This improvement may be an indication that shunting will improve their condition.
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Laurie Barclay, MD Stephanie Dionne Sherk
Ventricular shunting is performed in a hospital operating room by a neurosurgeon, a surgeon who specializes in the treatment of diseases of the brain, spinal cord, and nerves.