Doggy Detective Work: The Mysterious Case of the Blocked Bladder

Getting to the bottom of a health problem requires investigation. In this case, we look at a dog whose bladder stone had an unexpected cause.

By: kat reckling
Urate stones are uncommon in most dogs. By: kat reckling

A veterinarian has much in common with a detective, in that we both rely on clues to find what (or who) is causing the problem.

This was never truer than for a Cairn terrier, Fergie, whose bladder stone had an unexpected cause.

Fergie was a regular visitor to the clinic, with grumbly tummy upsets, sore skin or ear infections — nothing dramatic, but annoying issues nonetheless. But one Monday morning that all changed unexpectedly.


Rock-Hard Bladder

Fergie had spent Sunday night trying to urinate, squatting and straining — but with no result.

On Monday morning, when I felt Fergie’s tummy, it was obvious this wasn’t a simple case of cystitis. Fergie had a large, hard bladder, which immediately rang warning bells that the urethra (the tube draining the bladder) might be blocked.

An X-ray confirmed these suspicions. Fergie had a large bladder stone plugging the exit to her bladder, like a cork in a bottle. This is a serious problem because the back pressure of urine up the ureters (the tubes connecting the bladder to the kidney) can cause kidney damage.

Emergency Surgery

I removed the troublesome bladder stone, to Fergie’s immediate relief. She made a quick and uneventful recovery — but this wasn’t the end of the story.

It is usual when any bladder stone is removed to send it away for analysis. This tells us which mineral the stone is made of and why the stone formed in the first place. It gives the clinician a way of trying to stop more stones forming in the future.

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Stone Surprise

However, when Fergie’s report came back, I got quite a surprise. The stone was made up of urate crystals. Urate stones are very rare — mainly associated with Dalmatians (who have a peculiar metabolism) and a condition called a porto-systemic shunt (PSS).


This finding was puzzling because Fergie was clearly not a Dalmatian and in the past hadn’t shown obvious signs of a PSS. In any case, the urate was too important a clue to overlook, so we decided to test Fergie for a shunt. The results came back positive.

What Is a PSS?

In short, a PSS is a blood vessel that shunts blood past the liver. This allows waste products that the liver should break down to circulate round the body.

In Fergie’s case, abnormally high blood urate levels caused the bladder stone to form. If the shunt was not corrected, Fergie would grow more stones — and need repeated bladder operations.

Correcting the Shunt

I referred the dog to a specialist. Fergie had a detailed scan of her abdomen, which showed that her shunt was operable (not all of them are).

Another operation later, and Fergie was back to normal and better than ever. In fact, a lot of her nagging health problems vanished overnight, which makes it entirely likely the shunt had been responsible after all.

This video shows the coiling procedure performed during surgery to correct the shunt:

What Causes a Porto-Systemic Shunt (PSS)?

One of the liver’s jobs is to detoxify the blood of the natural toxins that result from digestion.

However, in the womb, the puppy receives nutrition direct from the mother’s “clean” blood supply and the liver doesn’t need to do this job, so a blood vessel shunts the circulation past the embryonic liver.

When the puppy is born, this shunt closes down and blood is rerouted through the liver. In some cases, though, this fails to happen and the shunt remains open. Now the liver is required to detox blood from the gut, but this supply just sails right on by.

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9 Signs of a Shunt

If you are wondering if your pet has this problem, here are some of the more typical signs:

  1. Stunted growth compared to other litter mates
  2. Slow recovery from a general anesthetic (such as for desexing)
  3. Intermittent sickness and diarrhea
  4. A tendency to eat unusual things (pica)
  5. A poor appetite
  6. Drooling saliva
  7. Bizarre behavior after eating, such as seeming spaced out or in a trance
  8. Regular infections
  9. Bladder stones

Shunts are generally congenital, which means they are present at birth, so the signs are most common in young animals.

Of course, these symptoms are general, and your pet may just have an upset stomach. But if you are worried, speak with your vet — who will investigate and, just like a detective, get to the bottom of things.


This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Dec. 17, 2018.


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