A kitten that stares at the wall 30 minutes after dinner, drools, and seems drunk is not being quirky. Portosystemic shunt (PSS) means blood from the gut skips the liver through a vessel 1 to 3 mm wide and arrives unfiltered at the brain, and the diagnosis rests on 2 tests that most clinics can run in 3 days. Cats hide this well for months, so the first clue is often a number on a blood panel rather than a symptom the owner noticed.
Three symptom groups, and the timing that separates them
1. Neurological. Hepatic encephalopathy shows up 30 to 120 minutes after a protein-heavy meal: staring, head pressing against a wall, circling, drooling, dilated pupils, and in worse cases a seizure. The tell is the timing, because a fasting cat for 12 hours usually looks normal again, and owners often describe a cat that is fine every morning.
2. Gastrointestinal. Vomiting 2 to 3 times a week, soft stool, appetite that swings from ravenous to nothing, and a body weight that plateaus. A 4-month-old that weighs what a 2-month-old should is the pattern, and the kitten is often the smallest of its litter by a visible margin.
3. Urinary. Ammonium urate stones form because the liver never converts ammonia to urea, and the crystals irritate the bladder. Watch for bloody urine, straining, and trips to the box every 20 minutes. Urine specific gravity often sits between 1.015 and 1.025 when it should be above 1.035, and a blocked male is an emergency on the same clock as any other obstruction: see the six signs of a blocked cat before you wait out the night.
A 4th group is easy to miss because it is not a symptom at all: poor anesthesia recovery, or a kitten that sleeps 20 hours a day and never plays.
Test 1: bile acids, fasting and 2 hours after a meal
This is the screening test that actually works in cats. Withhold food for 12 hours, draw the fasting sample, feed a normal meal, then draw again at 2 hours. Normal cats sit below 10 micromol/L fasting and below 15 micromol/L after eating. A shunt typically pushes the 2-hour value to 60 to 200 micromol/L, and the post-meal number is usually 2 to 4 times the fasting one. A single fasting sample misses a meaningful share of cases, which is why the pair is the standard.
Two traps: a cat fasted longer than 24 hours can read falsely low, and a cat that vomited the test meal has no post value at all. If the pair is borderline, repeat in 2 weeks rather than treat on one number.
Test 2: imaging that shows the vessel
Ultrasound finds a small liver, a large kidney, bladder stones, and a portal vein under 2.5 mm, and it can sometimes trace the shunt itself. CT angiography is the reference standard: it resolves to about 1 mm, and it separates an extrahepatic shunt, usually between the portal vein and the vena cava near the stomach, from an intrahepatic one inside the liver. That distinction decides the surgery, so most surgeons will not operate on ultrasound alone.
Supporting numbers that make the case stronger: blood ammonia 60 to 200 micromol/L against a normal under 50, BUN under 10 mg/dL, albumin under 2.5 g/dL, and red cells that are smaller than normal with an MCV under 40 fL.
Type decides the operation
An extrahepatic shunt with a vessel under 3 mm can often be closed in 1 session, with portal pressure watched and kept under 10 cmH2O. A wider vessel, or an intrahepatic one, needs gradual closure over 2 to 3 procedures using an ameroid constrictor or a cellophane band, spaced 4 to 8 weeks apart. Closing too fast causes portal hypertension, which shows up as vomiting, ascites, and a swollen gut within 24 hours.
| Type | Typical age at diagnosis | Vessel size | Closure plan | Cost (USD) |
|---|---|---|---|---|
| Extrahepatic, single | 3 to 12 months | 1 to 3 mm | 1 surgery, full ligation | 2,500 to 4,500 |
| Extrahepatic, wide | 6 to 24 months | 3 to 6 mm | 2 to 3 staged closures | 3,500 to 6,000 |
| Intrahepatic | 12 to 36 months | 4 to 8 mm | Coil embolization, 1 to 2 passes | 4,000 to 7,000 |
| Microvascular dysplasia | any age | no vessel seen | medical only, 4 to 6 small meals | 600 to 1,200 per year |
The 72 hours after ligation are the risky ones
Blood glucose can fall under 60 mg/dL within 24 hours, and seizures in the first 72 hours are the most common serious complication. Most cats stay 3 to 5 days, with glucose checked every 4 to 6 hours and ammonia once daily. Feeding restarts within 12 hours in small amounts, 4 to 6 times a day, because the liver now has to handle protein it never saw before.
Follow-up at 2, 4, 8 and 12 weeks
Bile acids are rechecked at 2 weeks, 4 weeks, 8 weeks, and 12 weeks; the values should fall toward normal each time, and a number that climbs again means the closure failed or a second vessel exists. Ultrasound or CT at 6 months confirms the shunt is gone. Neurological signs usually stop within 2 to 4 weeks, growth resumes within 8 to 12 weeks, and the cat moves onto a liver-support diet with moderate protein for at least 6 months.
If surgery is not possible
Medical management buys time, not a cure: lactulose to bind gut ammonia, an antibiotic to reduce ammonia-producing bacteria, a liver diet, and 4 to 6 small meals a day. Many cats managed this way stay comfortable for 6 to 18 months, and some for years, but the stones and the encephalopathy tend to return. Ask for a written plan with recheck dates, not a bag of pills.
If your cat also shows head tilt, nystagmus, or a drunken walk between meals, that is a separate vestibular pattern worth reading side by side: vestibular disease in cats explains how to tell the 2 apart in 10 minutes. For the money side, put the bile acid pair, the CT, and the surgery into one estimate with the cost calculator, because the gap between 2,500 and 7,000 USD is decided by which type the CT shows.
Terms mentioned in this article
Frequently asked
Are fasting bile acids enough to rule out a shunt?
No. A fasting sample alone misses a meaningful share of cats, because the liver can clear the fasting load while failing the meal challenge. The standard is a pair: 12 hours fasting, then 2 hours after a normal meal. A 2-hour value between 15 and 25 micromol/L is borderline and should be repeated in 2 weeks before any treatment decision.
At what age do shunt symptoms appear?
Most cats show something between 3 and 12 months, usually poor growth plus vomiting or a staring episode after a meal. Intrahepatic shunts are often found later, from 12 to 36 months, because the vessel is wider and the signs are milder. A cat of any age with unexplained small red cells and low BUN deserves the bile acid pair.
What happens if the shunt is never closed?
Medical management with lactulose, an ammonia-suppressing antibiotic, a liver diet, and 4 to 6 small meals keeps many cats comfortable for 6 to 18 months. Urate stones, bladder inflammation, and encephalopathy tend to come back, and each episode is harder to control. Surgery is the only option that removes the vessel itself.