Portosystemic Shunts (Liver Shunts) in Dogs & Cats
Portosystemic shunts (PSS) are abnormal blood vessels that bypass the liver, allowing toxins normally filtered by the liver to circulate throughout the body. These toxins — particularly ammonia — affect the brain, kidneys, and other organs. Shunts can be congenital (present from birth) or acquired secondary to liver disease.
At Sage Veterinary Imaging, CT angiography is our primary tool for diagnosing portosystemic shunts. This specialized study maps the entire portal vascular system in 3D, identifying the exact shunt location, size, and anatomy — information that surgeons need to plan the most effective corrective procedure.
SVI offers advanced ct services at our centers in Round Rock, Texas; Spring, Texas; and Sandy, Utah.
Portosystemic Shunts at a Glance
What Are Portosystemic Shunts?
In a normal pet, blood from the intestines flows through the portal vein to the liver, where toxins are filtered and nutrients are processed. In a portosystemic shunt, one or more abnormal vessels divert blood around the liver directly into the systemic circulation (typically the caudal vena cava or azygos vein).
Congenital shunts are present from birth and are usually single vessels. They are classified as extrahepatic (outside the liver, most common in small breeds) or intrahepatic (within the liver, more common in large breeds). These shunts result in a small, underdeveloped liver (hepatic atrophy) because the liver never receives its full blood supply.
Acquired shunts develop secondary to chronic liver disease and portal hypertension. Unlike congenital shunts, acquired shunts are typically multiple tortuous vessels that develop as collateral pathways when blood flow through the liver is obstructed. The treatment approach differs significantly from congenital shunts, making accurate differentiation essential.
Signs & Symptoms of Portosystemic Shunts
Shunt signs result from the accumulation of toxins (especially ammonia) that the liver would normally filter. Signs may be intermittent and often worsen after high-protein meals.
🚨 When to Seek Emergency Evaluation
Acute hepatic encephalopathy — characterized by sudden disorientation, head pressing, circling, blindness, or seizures — requires emergency veterinary care. These episodes can be triggered by high-protein meals, dehydration, or gastrointestinal bleeding, and require immediate medical management to reduce circulating toxins.
How CT Angiography Diagnoses Shunts
CT angiography (CTA) is the gold-standard imaging study for portosystemic shunt diagnosis. It provides a complete 3D map of the portal vascular system, showing the exact shunt anatomy that surgeons need for operative planning.
What CT Angiography Reveals
Shunt identification and classification — CTA identifies the exact shunt vessel, distinguishing extrahepatic from intrahepatic congenital shunts and differentiating single congenital shunts from multiple acquired shunts.
3D vascular mapping — Multiplanar reconstructions and 3D renderings show the shunt’s origin, course, and insertion point, allowing the surgeon to plan the approach and optimal constrictor placement.
Liver size assessment — CT accurately measures liver volume, which correlates with the liver’s capacity to handle increased blood flow after surgical shunt attenuation. Severely small livers may require staged correction.
Portal vein evaluation — CTA shows the portal vein size and branching pattern, which affects surgical prognosis. Adequate portal vasculature predicts better outcomes after shunt correction.
Additional anomalies — CT identifies concurrent conditions including urinary calculi (common with shunts), hepatic nodules, and other vascular malformations that affect management.
CT vs. Other Imaging for Liver Shunts
CT Angiography
Gold standard. 3D vascular map shows complete shunt anatomy, liver volume, and portal system. Essential for surgical planning.
Ultrasound
Can detect shunts in experienced hands. Useful screening tool. Limited by body size, gas, and operator dependence. Cannot reliably provide the surgical detail CT offers.
MRI
Can visualize shunts but takes much longer, requires prolonged anesthesia, and provides less spatial resolution for vessel detail than CT angiography.
Which Breeds Are Most at Risk?
Breeds at Higher Risk
Yorkshire Terriers have the highest prevalence of congenital extrahepatic shunts. Other commonly affected small breeds include Maltese, Pugs, Miniature Schnauzers, Shih Tzus, and Havanese. Intrahepatic shunts are more common in large breeds, particularly Irish Wolfhounds, Golden Retrievers, and Labrador Retrievers. Himalayan and Persian cats are predisposed among felines.
What to Expect During CT Angiography
CT angiography for shunt evaluation takes approximately 15–20 minutes under general anesthesia. A precisely timed intravenous contrast injection highlights the portal vasculature, and the entire abdomen is scanned in seconds. The timing of the contrast injection is critical to capture the portal venous phase.
Results are interpreted by a board-certified veterinary radiologist the same day. 3D reconstructions of the vascular anatomy are generated and shared with the referring veterinarian and surgeon. If surgery is planned, the imaging data helps the surgeon identify the exact shunt location and plan the best approach for constrictor or banding placement.
Why Choose Sage for Shunt Diagnosis
Schedule CT Angiography
If your pet has signs of a liver shunt or abnormal bloodwork suggesting hepatic dysfunction, CT angiography provides the definitive diagnosis and surgical roadmap.
Liver Shunt Imaging FAQ
Get Answers for Your Pet
A definitive shunt diagnosis and surgical plan start with CT angiography. Our team provides the detailed imaging your pet’s surgeon needs for the best possible outcome.