What is Liver Fistula?
In rare cases, dogs may have an abnormal connection between the arteries and veins in the liver. This is called a hepatic arteriovenous (AV) malformation, or a liver fistula. The oxygen-rich, arterial blood flowing into the veins creates portal hypertension, high blood pressure in the veins connecting the liver with other abdominal organs. This can cause fluid accumulation (ascites) and other systemic problems. An acquired portosystemic shunt (APSS) usually develops, a situation where the blood bypasses the liver and thus misses the cleaning, toxin flushing, process that normally takes place there. Without normal toxin removal, the blood becomes more and more polluted as it circulates. Severe cases will lead to symptoms of acute liver failure. Liver fistulas are usually congenital and manifest during the first year of a dog’s life. Rarely, they develop as the result of surgical injury or direct trauma to the liver, and sometimes they can also be caused by cancerous tissue in the liver. Untreated, they can lead to death or extreme symptoms that require euthanasia. Most conditions can be treated with surgery or by inserting a glue embolism to correct the blood flow.
Barriers between the veins and arteries in the liver can sometimes be absent or defective. This can cause the blood to circulate abnormally and bypass the liver. In dogs, veterinarians call this a hepatic arteriovenous malformation, or liver fistula. It is usually a congenital, inherited condition. Some cases can be treated with surgery.
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Symptoms of Liver Fistula in Dogs
Repeated vomiting and weight loss or failure to gain weight are usually the first signs of AV. Take your dog to see a veterinarian if you notice any of the following symptoms.
- Poor appetite
- Weight loss
- Failure to thrive
- Ascites – accumulation of fluid in the abdomen (peritoneal cavity)
- Murmur above the liver
- Excessive thirst
- Frequent urination
- Bloody diarrhea
- Gastrointestinal bleeding
- Hepatic encephalopathy (disorientation, circling, aggression, seizures coma)
AV’s are usually defined based on their size and visibility on a diagnostic image.
- Single fistula-type anomaly (AVF) – this type is larger, but easier to diagnose and treat
- Multiple microvascular malformations (AVM) –very small AV’s found in different parts of the liver; they are much harder to locate than AVF’s
Causes of Liver Fistula in Dogs
Congenital – most conditions have their origin in embryonic development. No specific prevalence among breeds has been noted.
Acquired – occasionally a condition can be acquired later in life. Some of the most common causes for this are:
- Surgery or biopsy of the liver
- Direct injury to the liver
Diagnosis of Liver Fistula in Dogs
The veterinarian will physically examine your dog and analyze blood and urine samples. It’s likely that your dog will need to fast for bloodwork that includes a serum bile concentration test. This test can show the presence of vascular anomalies in the liver, although it won’t be able to definitively diagnose an AV. The veterinarian will also try to eliminate other potential causes. Some infections or parasitic disorders could cause similar symptoms, as well as other more common vascular anomalies in the liver such as a portosystemic vascular anomaly (PSVA). Ascites, or fluid in the peritoneal cavity is one of the most specific symptoms of AV.
Diagnostic imaging is the best way to locate and definitively diagnose an AV. An abdominal ultrasound can identify most conditions and is the best non-invasive method. Portal venography is better for identifying multiple smaller AV’s. This usually requires surgery, but it is the best method for obtaining a complete picture of the liver. Contrast dyes are often injected to enhance the image. Biopsies of the liver are taken during surgery. These tests will not be safe for dogs with symptoms of acute liver failure.
The veterinarian will need your dog’s complete medical history as well a detailed description of the symptoms. Any prior surgeries or possible injuries to the liver will be important, especially in older dogs.
Treatment of Liver Fistula in Dogs
There are two main treatments for AV’s in dogs. Surgery, either a lobectomy or litigation of the nutrient artery, can sometimes correct the vascular abnormality. This is usually effective in treating a singular AVF, but if there are multiple small anomalies, they can be harder to correct with surgery. Studies have found that dogs who have surgery are more likely to experience recurrence and continued symptoms after the surgery.
The other treatment is interventional radiology which is the insertion of a glue embolism to redirect the blood in a normal circulation pattern. This has a slightly higher success rate than surgery since it is easier to correct a number of small AVM’s with this technique. It will still only be effective if all the problems are discovered and treated.
Either treatment plan will need to be evaluated by a veterinarian. Some conditions may not be treatable due to the number and location of the AV’s. Depending on the severity of the symptoms, it’s possible the veterinarian will recommend euthanasia. Some milder problems may be treatable with medication to help support the liver function and reduce symptoms. A high carbohydrate diet is often recommended to put less stress on the liver.
Recovery of Liver Fistula in Dogs
Recovery will depend on the veterinarian’s diagnoses and the treatment that is prescribed. If the condition is corrected, your dog may make a complete recovery. Some dogs with minor symptoms may require long-term medication or permanent diet changes to manage the condition. If this is recommended, it’s best to stick closely to the plan since liver failure can be a serious problem. Regular testing will be needed for the veterinarian to monitor your dog, and check for signs of recurrence.