Liver shunt in dogs: symptoms, tests and treatment

Overview

Normally, blood from the intestine, spleen and pancreas reaches the liver through the portal vein. The portal vein normally supplies around 70–80% of liver blood flow, so bypass substantially changes the organ's blood supply. The liver processes nutrients in this blood and makes harmful compounds harmless. With a shunt, some blood reaches the rest of the body without processing.

Bypassing also impairs liver growth because the liver misses growth-supporting factors normally delivered in portal blood. It may therefore remain smaller than usual and function less well. The condition causing neurological signs is called hepatic encephalopathy.

Around 10–20% of animals with a portosystemic vascular anomaly may have no clinical signs.

Causes

A congenital vessel can lie outside or inside the liver

A congenital shunt is an abnormal vascular connection present from birth. A connection outside the liver is extrahepatic, while one within liver tissue is intrahepatic. Most congenital extrahepatic shunts are single vessels, but several abnormal vessels can occur. Dogs with 2 or 3 congenital extrahepatic shunts have also been described. This differs from acquired bypass vessels opening because of high portal venous pressure.

Acquired connections result from resistance to blood flow

Chronic liver disease can raise portal vein pressure, causing blood to seek other routes. Acquired shunts are generally a network of vessels relieving high pressure. They are not closed like a correctable congenital connection, because closure can worsen the portal pressure problem.

Microvascular dysplasia affecting small liver vessels can also cause similar blood test changes without one large shunt vessel to close. An abnormal liver function test alone therefore does not establish correctable vascular anatomy.

Risk factors

Congenital extrahepatic shunts occur particularly in small and toy breeds. Examples include Maltese, Yorkshire Terriers and Poodles. Intrahepatic shunts are more common in large breeds, such as Irish Wolfhounds and Labrador Retrievers. Signs are often noticed before 1 year old. However, in a surgical series of 36 dogs, median age was 32.5 months, ranging from 5–99 months.

Acquired shunts can affect dogs of different ages and breeds. Risk relates to the disease causing portal hypertension. Congenital anomalies involve inherited susceptibility in some breeds. The precise shunt type is therefore investigated individually: breed does not determine diagnosis.

Typical symptoms

A puppy with a congenital shunt may remain smaller than littermates or grow poorly. Signs can be intermittent and more obvious after meals. You may notice the following:

• Slow growth, poor weight gain or weight loss.
• Vacant behaviour, behavioural changes or unusual tiredness.
• Unsteady walking, bumping into things or head pressing.
• Seizures or sudden visual disturbance.
• Vomiting, diarrhoea, poor appetite or constipation.
• Increased drinking and urination.
• Painful or difficult urination, or blood in urine.

Slower recovery from anaesthesia can also suggest a shunt. Ammonium urate stones may underlie urinary signs. Not every sign occurs in the same dog or at the same appointment.

Complications and consequences

Ammonia and other substances reaching the brain can cause severe encephalopathy. A urinary stone can block the urethra and prevent urination. Longstanding inadequate liver blood flow can impair growth and normal function.

Serious postoperative problems include portal hypertension, low blood glucose and seizures. A sudden portal pressure rise can stop intestinal movement and cause shock from bacterial toxins. Low blood glucose also occurs before intervention, particularly in young, very small toy-breed dogs. Seizures after shunt closure have been described in around 5–8% of dogs. They may develop during the first 7 days.

The outlook after surgical correction of a single extrahepatic shunt is generally good. Even with the rare multiple congenital vessel form, 12/14 treated dogs, or 86%, achieved a good or excellent clinical outcome. Median follow-up in this group was 1,253 days. This is follow-up duration rather than a life expectancy for all dogs with shunts.

Diagnosis at the vet

Blood tests provide clues and imaging shows vessels

Assessment reviews growth, meal-related signs, urination and any problems recovering from anaesthesia. Testing includes liver function measurements and urinalysis. Bile acids can be measured before a meal and 2 hours afterwards. High bile acids are consistent with a shunt but also occur in other liver diseases.

Ammonia, glucose, albumin and other blood results help assess functional consequences. Red blood cells may be smaller than usual, and mild anaemia can occur without a reduced red cell count. Urea and cholesterol may decrease. Urine may be more dilute than usual. Normal blood tests do not exclude a shunt in every case. Urine may contain ammonium urate crystals, and imaging looks for stones when needed. Not every urate stone appears on plain X-rays.

Precise anatomy is established before correction

Ultrasound may show plumper-than-usual kidneys alongside a small liver. An experienced examiner may identify the shunt vessel with Doppler ultrasound. However, intestinal gas and movement can obscure an extrahepatic vessel in particular. Contrast CT helps locate the vessel and plan intervention.

Images are also checked for other congenital abnormal vessels. Assuming there is only one vessel may leave some bypass circulation untreated. A liver biopsy can provide more information about small vessels and concurrent liver changes.

Treatment

Medical treatment reduces signs and prepares for intervention

Before surgery, nutrition and medication when needed stabilise your dog. The same measures matter if surgery is impossible or the vessels are acquired. Lactulose reduces ammonia absorbed from the intestine. Colonic bacteria break it into acids that convert ammonia into poorly absorbed ammonium. Diet adjusts protein quantity and source while ensuring adequate nutrition.

Severe protein restriction is not recommended for an asymptomatic shunt patient, particularly one already in poor condition. Dairy or plant protein may be selected for a dog with encephalopathy. Small, frequent meals can reduce meal-related brain signs. Weight, muscle condition and blood albumin are monitored to assess nutritional adequacy during treatment. Inadequate intake can increase muscle breakdown and worsen ammonia problems. Antibiotics and other medication are assessed individually. Your vet prescribes medicines and diet; do not start human treatment products at home.

Closure must be tolerated by the circulation

A correctable congenital shunt can be narrowed or fully closed if the portal circulation tolerates increased flow. Overly rapid complete closure can raise portal pressure dangerously. Portal pressure and abdominal organ responses are assessed during the procedure.

Gradual closure methods include a constricting ring or film placed around the vessel. Some intrahepatic shunts can be treated with coils introduced into the vessel. Surgery can be open or, in selected situations, laparoscopic. Strong evidence has not established one method as universally superior to every other.

Recovery and cessation of bypass flow are monitored separately

After surgery, pain relief and fluids according to the situation are needed. Medical and dietary treatment continues because liver cell regeneration and circulatory adaptation take time. Liver function tests are generally recommended 2–3 months after correction. If findings are abnormal, reassessment may take place at 5–6 months.

Normal ammonia or bile acids alone do not reliably prove vessel closure. Persistent signs or abnormal results may require further ultrasound or CT. A residual connection, reopened vessel or development of acquired shunts may underlie them.

Prevention

Puppy feeding or routine home care cannot eliminate a congenital vascular anomaly. Early investigation helps if growth falls behind or meals accompany behavioural and balance changes. Inherited breed susceptibility is considered in breeding and assessment of relatives' health information.

Preventing acquired shunts relates to treating underlying liver disease and managing portal pressure. An agreed diet and medication aim to reduce episodes in a diagnosed dog. Dehydration, constipation and infections are treated promptly because they can trigger encephalopathy.

Important for dog owners

Keep a diary of meals, episodes, growth and urination. Report a suspected or diagnosed shunt before every sedation or anaesthetic. Follow the prescribed diet, including treats, and give medication according to discharge instructions. Do not stop treatment simply because your dog seems lively after surgery.

At discharge, agree which signs are emergencies and when follow-up will take place. Record unusual sleepiness, staggering, vomiting and abdominal enlargement. Inability to urinate and seizures need prompt assessment.

Medication reduction is based on clinical condition and follow-up investigations. Some dogs need long-term treatment even after surgery. Ask the practice for a clear plan if neurological signs return or your dog refuses food.

Frequently asked questions

Can a dog manage with a liver shunt without surgery?

For some dogs, medical and dietary management is a long-term option if correction is impossible or not undertaken. However, narrowing a correctable congenital shunt is the preferred treatment option. Acquired bypass vessels are not closed in the same way: treatment addresses the underlying disease and signs.

Why are signs often worse after eating?

Blood from the intestine bypasses the liver through the shunt, leaving some harmful compounds unprocessed. This can cause hepatic encephalopathy brain signs. Signs may therefore be more apparent after a meal. Diet composition and medication are planned for your dog's condition.

Does a liver shunt show on routine blood tests?

Blood tests may provide suggestive clues, but results can also be entirely normal despite disease. Raised bile acids are not specific to a shunt. Imaging such as ultrasound and contrast CT establishes the abnormal vessel's location.

Are liver shunts inherited?

Congenital shunts involve inherited susceptibility in some breeds. Acquired shunts instead result from other liver disease and high portal pressure. The precise diagnosis therefore also matters when assessing relatives and breeding. Discuss the diagnosed anomaly with the breeder and your vet.

Can medicines stop once my dog looks healthy after surgery?

Medication reduction follows your vet's plan and follow-up investigations. Liver tissue must adapt to changed blood flow. Some dogs need long-term treatment even after correction. Normal ammonia or bile acids can also occur with a residual shunt.