Portosystemic Shunt in Dogs and Cats 🏥

By Dr Duncan Houston, DVM — Revised March 31, 2021

What is a Portosystemic Shunt?

A portosystemic shunt (PSS) is an abnormal vessel bypassing the liver—so blood from the stomach, intestines, pancreas, and spleen skips filtering and detox. Shunts are either congenital (born with) or acquired (developed later). Veterinary stats: ~80% congenital, 25–33% are inside the liver (intrahepatic), and ~0.18% of dogs are affected.

Fetal vs Postnatal Closure

In the fetus, blood bypasses the liver via the ductus venosus and normally closes within 3 days of birth. If it remains open, toxins accumulate—affecting growth and survival, especially in young pets.

Breed Predisposition & Risk

Purebreds have higher risk: Yorkshire, Maltese, Schnauzer, Poodle, Shih Tzu, Bichon, German Shepherd, Golden Retriever, Labrador, Doberman, Irish Setter, Australian Shepherd, and several Himalayan/Persian cat breeds. No sex bias.

Acquired Shunts

Acquired PSS occur secondary to liver disease (cirrhosis, hypertension, AV malformations). These also bypass the liver, causing toxin buildup.

Clinical Signs 🌡️

Toxin buildup leads to varied signs: stunted growth or weight changes, vomiting, diarrhea, lethargy, temporary blindness or seizures, altered behavior (zoning out, circling), poor coat, excessive drinking/urination. Signs depend on shunt location and toxin levels; often neurologic in nature.

Diagnosis 🔎

• Clinical evaluation: signs raise suspicion
• Blood tests: elevated pre- and post-meal bile acids
• Urinalysis
• Imaging: ultrasound, contrast portograms, nuclear scans
• Surgery: definitive diagnosis sometimes only during shunt repair

Treatment Overview

Canine/feline PSS managed via medical therapy or surgical correction.

Medical Management

Some pets do well with lifelong management: low-protein or highly digestible protein diets, antibiotics (to reduce ammonia-producing bacteria), lactulose (binds toxins), and avoidance of triggers (NSAIDs, sedatives, infection). Note: older pets often survive longer with medical care alone; younger animals less so.

Dietary Recommendations

Current guidance: small frequent meals with high-quality, moderate protein. Soy-based protein preferred in dogs; meat sources okay in cats. Vegetables are not recommended for feline liver function.

Surgical Repair

Surgery is a major option, especially for congenital shunts. Pre-op care includes stabilizing diet, antibiotics, and lactulose. Surgery success: ~85% overall, higher in dogs than cats. After uneventful surgery and improved bile acid levels, a normal diet may be resumed.

Post-Surgical Monitoring

• Continue medical care for weeks after surgery
• Recheck labs at 1 and 3 months—if bile acids still high, continue therapy
• Cats may need ongoing care; some benefit from a second surgery
• Persistently high bile acids in dogs with intrahepatic shunts aren’t always problematic if clinical signs resolved

Prognosis & Outcomes

Medical care only: ~33% do well; older, mildly affected pets do better. Dogs managed medically often euthanized within 10 months due to neurologic or hepatic deterioration. Surgical repair: ~85% success overall in dogs; cats have lower success—only ~33% long-term benefit.

Breeding Implications 🧬

Affected pets should never be bred—PSS runs in families and breeding stresses the system.

Key Takeaways 💡

• PSS allows toxin-filled blood to bypass liver cleanup
• Signs vary widely—focus on neurologic and GI changes
• Diagnosis through bile acid tests and imaging
• Options: lifelong medical management or surgery
• Surgical outcomes best in younger dogs; cats less responsive
• Supportive care essential post-operatively
• Genetic caution—don’t breed affected animals

Owner Support & Guidance

Early recognition and consistent veterinary involvement matter. Commit to follow-ups, regular liver monitoring, and steady diet plans for best outcomes.

References & Further Reading

Dr Duncan Houston encourages owners to connect with veterinary specialists, breed clubs, or liver-disease support groups as needed.

Content by Dr Duncan Houston, DVM 2025