Liver Shunts Page 2
DIAGNOSIS
Although signalment and clinical signs may strongly suggest the presence of a portosystemic shunt, a series of investigative steps must be taken to:
The latter two criteria are important when considering whether the shunt is amenable to surgical correction and the likely outcome of such surgery.
Blood chemistry and hematology panels usually show characteristic patterns of mild abnormalities that as a group suggest the presence of a portosystemic shunt. These include mildly elevated liver enzymes, low blood urea nitrogen and total plasma protein concentrations, hypogly- cemia (low blood sugar) and low serum cholesterol. Mild, nonregenerative anemia and microcytosis (undersized red blood cells) may also be present in all cases. Blood ammonia concentrations may also be increased, but samples must be rapidly analyzed soon after collection to detect such an increase. Urinalysis may reveal a low specific gravity and the presence of ammonium blurate crystals. Serum bile acid concentrations taken either after an overnight fast or 2 hours after a meal are usually confirmatory.
The next step is to identify whether the shunt is intrahepatic, extrahepatic, or microvascular. This generally requires specialized imaging techniques, and it is likely that dogs may need to be referred to appropriate specialists. Survey radiographs of the type normally taken in veterinary practices simply indicate the presence of a small liver
Ultrasonography is a useful, noninvasive tool for the detection of portosystemic shunts. Intrahepatic shunts are easily visualized: the liver usually appears small in size, there is reduced visibility of intrahepatic portal vessels, and an anomalous blood vessel may be obvious
In dogs with extrahepatic shunts the first two features are usually present, but the detection of the anomalous vessel is not so easy. Application of Doppler ultrasound, an advanced technique, may help in such cases, especially where there is a small extrahepatic shunt.
Contrast radiography, whereby a marker dye is injected into a vein draining the intestine and radiographs are taken immediately, allows ready visualization of the portal vein and shunting. This procedure is usually performed in combination with surgical correction (so that the dog has to be anesthetized only once) and is often referred to as operative mesenteric portography. A loop of small intestine is exteriorized (brought outside of the body) and a tube is placed in a jejunal vein. A water-soluble radiopaque dye is injected via the tube, and lateral and ventrodorsal radiographs are then taken. Where there is a shunt, the abnormal vessel is outlined as blood is diverted into the systemic circulation without appearing in the liver
Portal or transcolonic scintigraphy is an advanced technique whereby the uptake of radiochemicals from the intestinal tract is monitored. A radiochemical, usually technetium 99m pertechnetate, is administered via the rectum and first accumulates in the liver in normal animals. In dogs with portosystemic shunts the distribution of activity is altered as the radiochemical bypasses the liver and reaches the heart first. Although this does not identify the location of the shunt, it does provide an extremely accurate estimate of the degree of shunting, allowing the clinician to predict the likely success of management options and to follow up the success of surgical management.
Liver biopsy is indicated when there is no obvious shunt or if multiple extrahepatic shunts are identified (as seen in acquired portosystemic shunting). This may reveal hepatocyte atrophy, with small or absent portal vessels, and will allow histopathologic confirmation of micro- vascular disease.
MANAGEMENT
There are two broad management options: surgical ligation of shunts or medical management of the effects of shunting. The decision as to which is most appropriate needs to be made on a case-by-case basis depending on the type and location of the shunt, the age of the animal, and the severity of clinical signs. There may also be significant financial considerations on the part of the owner. Surgery wherever feasible, is generally believed to be the treatment of choice as it suggests the promise of normal liver function. Improvements in dietary and medical manage- ment of hepatic encephalopathy, however, mean that conservative treatments offer a reasonable prognosis for dogs that are not suitable for surgery
SURGICAL MANAGEMENT
Ligation of shunt vessels is an advanced surgical technique requiring a suitably experienced surgeon, careful selection and monitoring of general anesthesia, measurement of blood pressure in the portal vein and systemic circulation, and appropriate critical care support facilities. Such requirements usually necessitate referral to specialist centers, and this is especially true with intrahepatic shunts.
Single extrahepatic shunts are usually identified as tortuous, abnormal vessels. These are ligated close to the vena cava. A potential fatal complication is portal hypertension, which occurs when intrahepatic vessels are unable to cope with the additional volume of blood that is diverted to the liver after closure of the shunt vessel. Guarding against this requires careful monitoring of portal and systemic blood pressures and inspection of the intestines and pancreas for signs of cyanosis. Failure to alleviate the hypertension and pain, bloody diarrhea, and shock leading to death in 2 to 24 hours after surgery.
A 60% to 80% degree of ligation can usually be achieved without complications and is associated with an increase in the amount of portal blood that enters the liver and with improvements in the patient's clinical status. In some cases, the ligation procedure may be repeated on one or more later dates to progressively attain complete ligation. This un- fortunately necessitates additional costs and, with successive surgeries, increases the risk of perioperative, complications. On the other hand, repeat surgery may not be necessary as some partially ligated shunts appear to spontaneously occlude. The prognosis for dogs with partial ligation is guarded because approximately 50% show recurrence of clinical signs at an average of 3 to 4 years after surgery. Ligation of intrahepatic shunts is technically more difficult and is associated with higher risks of fatal complications. Such cases may be best managed conservatively.
MEDICAL AND DIETARY MANAGEMENT
With better understanding of the pathophysiology of hepatic encephalopathy, it has become possible to prescribe specific therapies that provide a reasonable prognosis for those dogs with portosystemic shunts that are not corrected surgically. The primary objective of medical management is to eliminate the clinical signs associated with hepatic encephalopathy. Other goals include minimizing lower urinary tract disease and reducing the metabolic load on the liver. The chief components of medical management strategies are dietary modifications and oral antibiotics.
Medical management is indicated for all dogs with acquired shunts and all dogs with microvascular shunts. It should also be used for a period in those dogs that are about to undergo surgical ligation. This will allow the veterinarian and owner to establish the extent to which the condition can be managed medically, in case it is not possible to completely ligate the shunt at surgery. medical management is also indicated in those dogs whose owners are unable to afford the cost of referral to a specialist surgical facility or whose owners are unwilling to accept the significant risk of perioperative mortality. All dogs undergoing surgical ligation should continue to receive medical therapy for 2 to 4 weeks post- operatively. Finally, some degree of medical therapy may be required in dogs with partially ligated shunts.
Dietary manipulations for the control of hepatic encephalopathy are designed to limit neurotoxin production, which occurs principally in the large intestine, and to reduce the subsequent absorption of these toxins into the portal vein .The major toxins are all derived from nitrogenous materials (protein and urea) and are synthesized by bacteria found within the large intestine. The production of these toxins is reduced by limiting the amount of protein fed and ensuring that the dietary protein is high quality and very digestible. These steps reduce the amount of protein that reaches the large intestine; further reductions can be attained by feeding smaller meals more frequently to maximize the digestive capacity of the small intestine.
Specific diets with restricted protein contents are available from veterinarians. These are ideal because they provide a balanced protein-calorie intake, which is important for the stable control of hepatic encephalopathy. Including dietary fiber in the daily ration assists in acidifying the colonic environment and limiting toxin production and also acts as a mild laxative to increase the elimination of toxic factors in feces. Lactulose, a soluble fiber, is often used as a supplement for this purpose and can be readily purchased from pharmacists. Supplementation with zinc salts also im-proves the detoxification of ammonia and the control of hepatic encephalopathy. A veterinary diet specifically designed and tested for the management of liver disease and portosystemic shunts is available in Europe; it is unique in combining a restricted protein content with increased zinc and added dietary fiber.
Antibiotics are used in most cases to reduce the bacteria within the large intestine that are responsible for the production of neurotoxins. Orally administered neomycin is commonly used for this purpose and is often used in combination with lactulose in both the short and long-term medical management of portosystemic shunts.
SUMMARY
Portosystemic shunts are serious conditions in dogs and require significant efforts to diagnose and treat. Specialized surgical techniques, in association with advances in medical and dietary management, allow the condition to be effectively managed and provide a reasonable quality of life.
My own little pup Harley has a liver problem, possibly a shunt as the bile acid tests and blood tests all point in that direction, however, when we took her to Edinburgh Veternary Hospital the Scan showed up just a small dark liver, with no apparant external shunt visible, they now wish to do the liver Biopsy , then if its found to be an internal shunt, operate .
She is doing well on the antibiotics and is leading a normal life with special diets ect, so at this point in time im not going to go ahead with the biospy as it carrys a huge risk, perhaps she has just a small liver, I hope so but the blood and bile acids seem to point to otherwise
Harley was fit and healthy , when I bought her, this just happened a month or so after having her
the cost of keeping a dog with these problems must also be considered, the operation costs £4000, My vets bills so far are around the £1000 mark, and that just for tests and specialists visits to hospital
WHAT IS A LIVER SHUNT. AN EASY GUIDE..............
A Liver Shunt is a condition in which a portion of the blood in the body by-passes the liver and goes directly to the heart. Toxins especially ammonia build up in the blood stream and the dog has seizures due to increased ammonia levels. The liver is usually smaller than normal and will have decreased liver function. Secondary liver infection can occur but this plays a minimal role in the liver shunt syndrome. It is the bypassing of the blood thru the liver that is the major problem.
The symptoms of liver shunt can start to appear at almost any age. Dogs with a liver shunt are usually very thin dogs who pick at food. They not only have a poor appetite but they can become lethargic, dizzy, and stagger. They may try to climb out of their pen, climb higher on you and cry and throw their head far back after eating, and they may go into convulsions. Plesse note these sympons mimic hypoglycemia, and a lot of dogs have been lost through not being tested for a shunt, breeders may think they are weak puppies or brain damaged, but they can survive if diagnosed quickly enough.
for more info click http://www.lbah.com http://henceforths.com/liver_shunt.htm
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