Shunts
Shunts are medical devices surgically implanted to alleviate fluid pressures in the body, commonly utilized in cases of blocked vessels. Two primary types of shunts include ventriculoperitoneal shunts, which drain excess cerebrospinal fluid from the brain in conditions like hydrocephalus, and portacaval shunts, which help manage elevated blood pressure in the portal veins associated with liver complications. Hydrocephalus can occur in infants or adults and is marked by symptoms such as an enlarged head, seizures, or severe headaches. The surgical process for both types typically involves anesthesia, incisions, and the careful placement of catheters to redirect fluid or blood flow. While shunts can be life-saving, they come with potential complications, including blockage, infection, and in the case of portacaval shunts, possibly worsening liver function. Early detection and intervention are crucial for improving long-term outcomes in patients with conditions requiring shunt placement. Alternative treatments, like medications and dietary changes, may also play a role in managing these conditions.
Shunts
Anatomy or system affected: Abdomen, brain, circulatory system, gastrointestinal system, head, liver, nervous system
Definition: Surgically inserted tubes that are used to bypass blocked vessels that normally allow fluid to move from one region of the body to another
Indications and Procedures
The surgical placement of shunts is performed to reduce fluid pressures when the vessel that normally carries the fluid is blocked. Among the many kinds of shunts, two major types are ventriculoperitoneal and portacaval. Ventriculoperitoneal shunts are used to remove excess fluid from the brain in hydrocephalus. Shunts used to decrease blood pressure in the portal veins are known as portacaval shunts.
Hydrocephalus is a condition characterized by an excessive amount of cerebrospinal fluid in the brain caused either by too much cerebrospinal fluid production or by the blockage of its flow. Hydrocephalus can occur at birth or be caused by head trauma, infection, or brain hemorrhage. If it occurs at birth, the main signs are an enlarged head that continues to grow more rapidly than normal. An infant’s skull bones have yet to fuse, and the fluid pressure causes them to expand. The infant may have seizures, vomiting, abnormal reflexes, and other neurological signs. If hydrocephalus occurs in an adult, when the skull bones cannot expand, the pressure on the brain causes headaches, mental deterioration, loss of consciousness, and, if not treated, death.
Physicians use computed tomography (CT) scanning or magnetic resonance imaging (MRI) to find the blockage. The patient is then prepared for surgery to have a shunt inserted to drain the accumulating fluid. After the individual is anesthetized, the head is prepared for the operation. An incision is made through the skin of the head, and a hole is drilled into the skull, a procedure called a craniotomy. A catheter that is part of the ventriculoperitoneal shunt is inserted into the ventricles of the brain and passed under the skin into the abdominal cavity, which is lined by the peritoneum. The peritoneum is a large membrane capable of absorbing the excess cerebrospinal fluid.
Portacaval shunts are used to reduce the blood pressure in the veins carrying blood from the digestive tract to the liver. Patients with abnormally elevated blood pressure in these veins have portal hypertension. This pressure reduces blood flow from the esophagus, stomach, and intestines, which leads to a pooling of blood and an engorgement of these vessels that may lead to their rupturing. Fluid leaking from the portal vein accumulates in the abdominal cavity, a condition known as ascites.
The most common cause of portal hypertension is cirrhosis of the liver, in which the liver is diseased and scar tissue forms. This scar tissue can block blood entering the liver from the portal vein and lead to portal hypertension. Occasionally, a thrombus (blood clot) will form in the portal vein and cause portal hypertension when the liver is not diseased. The patient may have ruptured vessels that bleed into the digestive tract, causing the feces to appear black. If the physician suspects portal hypertension, they will perform an ultrasound and arteriography to view the vessels.
A portacaval shunt operation may be necessary to reduce the pressure in the portal vein if other treatments have failed. In this surgical procedure, the patient is anesthetized and prepared for a major abdominal surgery called a laparotomy. An incision is made into the abdominal cavity, and the portal vein is exposed. The surgeon must then carefully place a catheter between the portal vein and another large abdominal vein, the inferior vena cava, which helps return blood to the heart from the lower body and the abdominal cavity. Another surgical option is for the surgeon to connect part of the portal vein to the inferior vena cava directly without the use of a catheter. The portacaval shunt diverts some of the blood that normally goes to the liver directly into the inferior vena cava, thus reducing the pressure within the portal vein.
Uses and Complications
The major problem associated with the ventriculoperitoneal shunt is the fact that it will need to be replaced as the infant grows. It is also possible for this tube to become blocked or infected. If the shunt remains in place for a long period of time, it may spontaneously penetrate an abdominal organ.
Portacaval shunt operations reduce the high blood pressure in the portal vein and help prevent bleeding. Unfortunately, they do not significantly improve liver function in most patients and may even cause further liver damage.
Perspective and Prospects
Early detection and treatment of increased intracranial pressure (pressure on the brain) in hydrocephalus and increased blood pressure in portal hypertension are important to the long-term health and survival of the patient.
Early treatment of hydrocephalus with shunt placement prevents further neurological damage and, if the increase in brain pressure is rapid, may even be necessary to prevent death. Drugs, such as acetazolamide that inhibit the formation of cerebrospinal fluid may, in certain cases, prevent the need for shunt operations. These agents will likely prove most effective in patients with mild disease.
Physicians may try to stop bleeding from ruptured vessels that is caused by portal hypertension by injecting a solution into the veins to seal them (sclerotherapy). Dietary restriction of salt (sodium) and diuretic drugs may be tried to reduce blood pressure, vessel engorgement, and ascites fluid accumulation.
Bibliography
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