Liver shunt

A liver shunt – medically known as a portosystemic shunt – is a vascular malformation, either congenital or acquired, where blood simply bypasses the liver. Unfiltered. Directly into the body. Normally, blood from the digestive tract first passes through the liver, which detoxifies it, before entering the systemic circulation. In the case of a liver shunt, this step is skipped.

The liver does far more than just detoxification in the body: it stores nutrients and produces proteins for countless bodily functions. If blood bypasses it, toxins build up – resulting in metabolic disorders and neurological symptoms.

Types of Liver Shunts

In dogs, there are basically two main forms:

1. Congenital liver shunt: The most common form, usually in young dogs. From birth, there is an abnormal connection between the portal vein and the systemic circulation. Depending on the location of the shunt, a further distinction is made:
   Intrahepatic shunt: The shunt is located within the liver. Larger breeds are more frequently affected – such as Golden Retrievers or Irish Wolfhounds.
   Extrahepatic shunt: Here the shunt is located outside the liver. Small breeds are more often affected: Yorkshire Terriers, Maltese or Miniature Schnauzers, for example.
2. Acquired liver shunt: This develops as a result of an existing liver disease, such as cirrhosis. If the liver is severely damaged, the body creates bypass routes – a mechanism that exacerbates rather than solves the problem. Affected are mainly adult dogs.

Causes of a Liver Shunt

In the case of congenital liver shunts, the exact cause has not been fully clarified to this day. Genetic factors obviously play a role, as certain breeds are significantly more susceptible than others. In acquired shunts, the connection is clearer: the malformation occurs because a pre-damaged liver can no longer process blood effectively.

Symptoms of a Liver Shunt

What often confuses owners: the symptoms are non-specific and vary depending on the severity and how much blood actually bypasses the liver. First signs often appear in young dogs – from a few weeks to about one year of age. In acquired shunts, however, they can also occur significantly later.

Typical signs at a glance:

1. Behavioural changes: Lethargy, disorientation, sudden weakness – so-called lethargic episodes in which the dog appears dazed. Notably, the signs often worsen after eating because the body is exposed to more toxins following digestion.
2. Neurological symptoms: Some dogs develop hepatic encephalopathy, a brain dysfunction caused by toxins in the blood. Trembling, seizures, head pressing (the dog presses its head against walls or furniture), disorientation, uncontrolled movements – the spectrum is broad.
3. Poor growth and developmental delays: Dogs with a liver shunt struggle with growth and weight gain. They often appear smaller and more delicate than their peers – which is sometimes mistakenly dismissed as a breed characteristic.
4. Gastrointestinal problems: Diarrhoea, vomiting, reduced appetite. Some dogs also show intolerances to certain foods.
5. Excessive drinking and urination: Many affected dogs drink more water than usual and consequently urinate more frequently.
6. Bladder stones or urinary crystals: Dogs with a liver shunt often develop urinary tract problems – bladder stones or crystals in the urine – because elevated toxin levels put strain on the kidneys.
7. Seizures: In severe cases, seizures may occur, triggered by the accumulation of toxins in the brain.

Diagnosing a Liver Shunt

If a liver shunt is suspected, the vet carries out several tests. The findings complement each other – a single value alone rarely suffices for a definitive diagnosis.

1. Blood tests: Blood analyses often show elevated liver enzyme levels and low urea concentration. Ammonia levels are frequently raised, indicating insufficient detoxification.
2. Bile acid test: The bile acid level is measured before and after a meal. Elevated values indicate that the liver cannot adequately detoxify the blood.
3. Imaging techniques: Ultrasound and CT scans help visualise the structure of the liver and blood flow. This allows the shunt to be located and clarifies whether it is intrahepatic or extrahepatic.
4. Liver biopsy: In certain cases, a biopsy is performed to determine the exact cause of the liver shunt.

Treating a Liver Shunt

Treatment depends on whether it is a congenital or acquired shunt and how pronounced the symptoms are. In principle, two approaches are available:

Medical Treatment

• Dietary adjustment: Dogs with a liver shunt are often placed on a protein-reduced diet to reduce the formation of ammonia and other toxins in the blood. This relieves the liver and helps control the symptoms.
• Medications: Lactulose and antibiotics reduce the formation and absorption of toxins in the gut. Lactulose binds ammonia in the intestine and excretes it via faeces; antibiotics control the bacteria that produce this ammonia in the first place.
• Medications for seizure prevention: If seizures occur, anticonvulsants are prescribed to reduce their frequency and severity.

Surgical Treatment

In the case of a congenital liver shunt, surgery is often the most effective approach. The surgeon attempts to correct the abnormal blood flow by closing the shunt. Special rings are frequently used to gradually narrow the shunt – this gives the liver time to adapt to the altered flow conditions.

• Surgical success: The success rate for extrahepatic shunts is high. For intrahepatic shunts, the procedure is significantly more complex; prospects depend on the individual case and the dog’s general health.

Prognosis for Liver Shunt

The prognosis varies considerably. If a congenital shunt is operated on – ideally early – many dogs can lead a largely normal, healthy life. If surgery does not take place, the course depends on the severity of the symptoms and how well the dog responds to medical therapy.

For acquired liver shunts, the prognosis is usually poorer because serious underlying conditions such as cirrhosis are involved. The focus then shifts from cure to alleviating symptoms and maintaining quality of life.