In medicine, the shunt has two related definitions. In either case, it is a passageway that is not normally present in the body, which allows fluid communication between two areas. This can either be a congenital condition that represents an initial abnormality of the body and creates medical dysfunction, or it can be what is called a created or acquired condition that serves to compensate for some type of medical problem. There are numerous examples of both shunts.
Congenital shunts may occur in many different body areas. Some of the best known are related to congenital heart defects, and are essentially holes that exist between two parts of the heart that are ordinarily closed off from each other. Holes in the ventricular and atrial septum can be problematic because they result in blood shunting between the right and left ventricles or atria, which can either increase pressure in the chambers or send unoxygenated blood back to the body.
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Not all shunts are abnormal. People are born with several small holes in the heart or above it that close in the first few days or months of life. These communications only become abnormal if they stay open too long and begin to interfere with function.
There are other congenial shunt examples like the portosystemic shunt (PSS). Most often found in certain dog breeds, it involves failure of a normal congenital shunt, the ductus venosus, to close. When this occurs, it can bypass the way fluids are sent to the liver, which can cause conditions like failure to thrive and toxin build-up.
In other circumstances, shunting is desirable to create some connection that didn’t formerly exist or to help with fluid drainage. An acquired or created shunt may treat many different types of conditions. One common type of shunt is used to drain fluid that is accumulating in areas like the brain. If people have recurrent hydrocephalus, surgeons may use a shunt to help drain off excess cerebral spinal fluid so that swelling is reduced and impact on the brain is lessened. The shunt is usually connected to another tissue area that will easily withstand and absorb the fluid.
Just as congenital shunting is common in cardiac defects, many heart defects are repaired or palliated with surgical shunting. Nowhere is this more common than in treatments for single ventricle conditions like hypoplastic right or left heart or tricuspid atresia. Surgeons use a series of palliative procedures with shunts to normalize heart function.
The Glenn surgical procedure connects the superior vena cava to the small pulmonary veins, and the Fontan connects the inferior vena cava to the superior vena cava. This creates an environment where returning blood from the body bypasses the heart and passively flows into the lungs, reducing heart workload. For certain heart defects, cardiothoracic surgeons may also create holes between the ventricles or atria to cause shunting if one side of the heart is somehow impaired.