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November 22, 2009

Urolithiasis (bladder stones)

Meet "Miss Scarlet the Grange Dog". She came to visit us a few weeks ago with the complaint of not feeling well and having to urinate all the time. The only problem we could find on physical exam was a small amount of malodorous vaginal discharge. Since she had never been spayed, we had to consider that she might have pyometra (infection in the uterus). Surgery to remove her uterus and ovaries was scheduled, and antibiotics and pain medicines were started. When Miss Scarlet was anesthetized we were able to palpate her abdomen a little better. While she was awake, she kept her stomach muscles so tight that we could not effectively palpate. A very hard structure was felt in the caudal abdomen (towards her tail end) -- in the area of the bladder. Since there should not be any hard objects in this area, it was likely that she had, along with the infected uterus, a stone in her bladder. The medical term for this is urolithiasis.

Surgery consisted of opening the abdomen, cutting into the bladder and removing a large "rock", flushing the bladder and urethra, and then suturing the bladder closed. Next, the uterus and ovaries were removed because of her pyometra. All went well and Miss Scarlet was returned to her owner a new "lighter" dog.

This is a picture of the freshly removed stone.

This picture shows some objects for size reference. Scarlet is a 10# mixed breed terrier. As you can imagine from the size of the stone, there wasn't much room left in the bladder for urine. This reason, combined with the irritating nature of the stone, would make it so that Miss Scarlett felt like she had to urinate all the time. Add to this the irritation and discomfort from the uterus and you can understand why she didn't feel 100%.

Here are some examples of stones we have removed from other patients. Sometimes there is just one, sometimes there are hundreds -- like small gravel. These stones are very hard. Often the stones are passed out the urethra before they get large enough to cause trouble. If they are not passed they can irritate the lining of the bladder, cause bloody urine, and make the dog feel like it has to urinate often. The stone can also temporarily (or permanently) block the passage of urine, and when this happens, it is a medical emergency. Surgery must be performed immediately to remove the stone or stones so that the dog can urinate.

Crystal formation is enhanced in urine that is alkaline (has a basic pH), and is inhibited in urine that has more acidic pH. Diet is a big contributing factor to the pH of the urine. Meat based diets tend to make more acidic urine, and plant based diets make more alkaline urine. Bacteria, which like to grow in an alkaline pH, make by-products that also contribute to crystal formation. Bladder stones in dogs are sometimes found following cases of infection in the bladder (cystitis). The inflammation and bacterial by-products form debris in the bladder which provide a starting place (or nidus) for the crystals to begin forming. Once the crystals start, they can form onto each other and build and build until they make stones. So you can see that urine pH and bacterial infection go hand in hand with urolithiasis.

Not all stones are caused from inflammation, some dogs such as Dalmatians, produce bladder stones because they cannot metabolize certain substances well. In the case of some Dalmatians, they cannot metabolize uric acid and so they make uric acid stones. This type of stone formation can be possibly corrected or prevented with special diets. Other dogs, such as Schnauzers just seem predisposed to form stones for some unknown reason.

Bladder stones can look very impressive on a radiograph as shown above. This radiograph is not from Miss Scarlett, but of a dog that had the largest stone in the above stone comparison.
Can you see the more dense central portion of the stone? This could be a different type of stone within the larger stone. It is not unusual to have multiple types of stone within the bladder at the same time. It sure looks uncomfortable to me!