This disease is a mostly congenital vascular malformation of the liver that was first described in 1949. The "shunt" is a connecting vessel that directs blood from the body's circulation past the liver directly into the main vein and thus unfiltered to the heart. The liver's inability to detoxify the blood leads to gradual internal poisoning of the animal.
In dogs and cats, liver shunts are congenital in the majority of cases. As the condition is more common in certain breeds of dog, a hereditary cause is suspected. However, there is no definitive proof of this yet.
To better understand how a shunt develops, let's take a look at the vascular connections and blood flow in healthy animals. During the embryonic phase, there is a connection between the portal vein and the main vein, as the liver does not yet have any function at this stage. The fetus (the embryo after the organs have formed) is supplied with filtered maternal blood via the umbilical vessels. Normally, this connecting vessel atrophies after birth and blood from the body is directed to the liver. If this vessel does not regress or if other vascular connections form, the blood from the body bypasses the liver, which is then undersupplied and can no longer perform its filtering function.
In terms of anatomical location, a distinction is made between extrahepatic (outside the liver) and intrahepatic (inside the liver) liver shunts. Extrahepatic shunts are more common in small dog breeds, while intrahepatic shunts are more common in large breeds. Overall, however, extrahepatic shunts occur twice as often as intrahepatic shunts.
Unfortunately, a portosystemic shunt can manifest itself in many different ways. In some animals, a small liver shunt is sometimes discovered only by chance, as they live for years without any noticeable symptoms. In others, however, clear signs of the disease can already appear in puppyhood. The symptoms can be divided into three groups according to their origin.
The lack of detoxification can lead to neurological symptoms such as depression, restlessness, ataxia (impaired coordination of movement), or blindness. These symptoms are more pronounced after eating and are referred to as hepatoencephalopathy (a disease of the brain caused by the liver). Meat-based foods in particular contain high levels of protein, which is broken down in the intestine, releasing large amounts of toxins into the blood that cannot be filtered out by the liver. Reducing the amount of meat in the diet therefore usually leads to an immediate improvement in symptoms in affected animals, which can be interpreted as an indication of a liver shunt.
Impaired liver function causes gastrointestinal symptoms such as vomiting, diarrhea, loss of appetite, and weight loss of varying intensity. Cats in particular experience increased salivation. Urinary tract symptoms may also occur. These include increased drinking, frequent urination, urinary tract infections, and urinary stones.
Animals affected by a shunt often show growth retardation and poor muscle development. As puppies, they are usually the smallest of the litter.
After a thorough clinical examination and a detailed preliminary report, your veterinarian will have initial indications of a liver shunt, but at this point can only make a tentative diagnosis. Blood tests are very important for further diagnosis, as changes in various parameters provide valuable information about a potential liver shunt. However, imaging techniques are essential in order to make a definitive diagnosis. Ultrasound and computed tomography are the preferred methods and are considered the "gold standard" in diagnostics.
The clinical symptoms can be significantly improved with a low-protein diet and special medication. However, medication alone cannot stop the progression of the disease and the associated damage to the liver.
The aim of surgery is to close the connecting vessel or shunt. In order not to overload the liver, which has become accustomed to a low blood flow, the closure must be carried out gradually, sometimes in two consecutive operations. The use of a special implant allows the shunt vessel to be closed slowly, so that in many cases a second operation is not necessary and fewer complications occur.
Another treatment option is embolization, which involves closing the vessel from the inside. This involves inserting a small wire coil into the shunt vessel via a catheter that is inserted into a vein in the leg using a guide wire. This coil is coated with special fibers that cause blood clotting, which slowly closes the vessel.
If the shunt vessel can be successfully closed during surgery, the chances of a complete recovery are good. After an average of two to four months, the underdeveloped liver has recovered and can once again perform its metabolic functions fully. The affected animals' food intake and physical development return to normal, and their life expectancy is once again the same as that of healthy animals.
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