Portosystemic (Liver) Shunt

The signs of PSS are caused by hepatic encephalopathy — the neurological effects of toxins (especially ammonia) that the liver fails to clear. They often worsen after eating, because digestion produces a surge of ammonia from protein breakdown.

• Stunted growth — affected animals are often the smallest in the litter
• Disorientation, aimless wandering, or appearing "spacey"
• Staring into space or pressing the head against a wall
• Seizures, which may occur several hours after a meal
• Circling, incoordination, or stumbling
• Excessive drooling (ptyalism)
• Behavioral changes — unusual aggression, depression, or sudden personality shifts
• Increased thirst and urination
• Vomiting, diarrhea, or poor appetite
• Ammonium biurate crystals in the urine, leading to recurrent urinary tract symptoms or bladder stones in young animals

Neurological signs that wax and wane — especially in a small, slow-growing puppy or kitten — are a classic red flag for a liver shunt.

Portosystemic shunts are broadly divided into two types based on cause and anatomy:

• Congenital extrahepatic shunts: a single aberrant vessel outside the liver, most common in small and toy breeds — Yorkshire Terriers, Maltese, Shih Tzus, Miniature Schnauzers, and Pugs among dogs; Persians and Himalayans among cats. The vessel is a remnant of fetal circulation that failed to close after birth.
• Congenital intrahepatic shunts: the shunting vessel passes through the liver tissue itself; more common in large and giant breeds such as Irish Wolfhounds, Golden Retrievers, and Labrador Retrievers. These represent persistence of the ductus venosus, a fetal vessel.
• Acquired (multiple) shunts: develop secondary to chronic liver disease and portal hypertension in adult animals; these are multiple small vessels rather than a single large one, and surgical correction is not possible — medical management is the approach.
• Genetics: certain breed lines have a higher incidence, suggesting a heritable component, particularly in Yorkshire Terriers

Diagnosing a portosystemic shunt requires a combination of bloodwork, specialized functional tests, and imaging. The full picture is usually assembled in one or two visits.

• Bile acid stimulation test: the most important screening test — bile acids are measured before and two hours after a small meal; an exaggerated post-prandial (after-meal) rise strongly suggests hepatic (liver) insufficiency from a shunt
• Blood ammonia level: elevated ammonia, especially in a young animal with neurological signs, raises immediate suspicion
• Complete blood count and chemistry panel: may show low BUN (blood urea nitrogen), low albumin, abnormal liver enzymes, or microcytosis (small red blood cells — a hallmark of liver shunts)
• Urinalysis and urine sediment: ammonium biurate crystals in a young animal are highly suggestive
• Abdominal ultrasound: an experienced sonographer can often identify the shunting vessel directly and assess liver size; our on-site ultrasound capability means no wait for outside imaging
• CT angiography: computed tomography with contrast maps the shunt vessel precisely and is essential surgical planning — our in-house CT scanner makes this possible without referral

A single congenital extrahepatic shunt is best treated surgically — and outcomes are excellent in well-selected patients. Intrahepatic shunts can also be corrected surgically but carry higher technical complexity. Medical management controls symptoms but does not correct the underlying problem.

• Medical management (pre-surgery and for non-surgical candidates): a low-protein, high-quality diet reduces the ammonia load; lactulose (an osmotic laxative) traps ammonia in the colon and speeds its elimination; antibiotics reduce ammonia-producing intestinal bacteria
• Surgical correction — ameroid constrictor or cellophane banding: devices placed around the shunting vessel slowly cause it to close over four to eight weeks, allowing portal blood to gradually redirect through the liver without a sudden change in pressure. See Portosystemic Shunt Ligation
• Post-operative monitoring: bile acid tests and clinical assessment at scheduled intervals confirm successful closure; some animals require ongoing medication during the gradual closure period
• Bladder stone management: ammonium biurate stones in the bladder are addressed separately — dietary dissolution or surgical removal via cystotomy — once the shunt is corrected

The prognosis after successful single-shunt closure is very good. Many young dogs and cats treated early grow to lead entirely normal lives. Even older animals with chronic shunts often benefit significantly from correction.

If you have a small-breed puppy or kitten that is significantly smaller than littermates, has episodic neurological signs, drools excessively, or has been found to have unusual lab values, a liver shunt workup is warranted. The bile acid test is a simple screening step that can be done at a wellness visit. The sooner a congenital shunt is identified and corrected, the better the outcome — young animals with minimal liver damage before surgery have the strongest recoveries. Book an appointment so we can begin the workup without delay.