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Dog: Urolithiasis

General information

Other common/scientific names: bladder stones, urinary tract stones, urinary calculi, cystic calculi, urethral stones, urethral calculi, kidney stones

Urolithiasis is defined as calculi or stones in the urinary tract. The urinary tract consists of the kidneys, ureters (tubes that carry urine from the kidney to the bladder), the urinary bladder and the urethra that carries urine outside the body. Urinary stones can be found in any of these structures. However, when we speak of urolithiasis in dogs, we are usually referring to stones in the bladder and/or urethra.

The formation of bladder stones is very much like the formation of a pearl inside an oyster. The stone forms because of an irritant or very small particle acting as a nidus where minerals are deposited on its surface, layer by layer. As the stone enlarges, it causes irritation to the lining of the bladder which can result in bleeding and thickening of the bladder wall. The chance of developing chronic urinary tract infection is increased with bladder stones.

These urinary tract stones are made up of different mineral compositions. The three most common types of stones seen in dogs are struvite stones, oxalate stones and urate stones. Stones of mixed composition can also occur.

The most immediate concern for a dog with urolithiasis is that the urinary opening becomes obstructed by the stones and the dog is unable to urinate. This tends to be more of problem with male dogs since their urethras are longer and narrower. Dogs which are unable to urinate because of an obstruction will build high levels of toxins in the blood and experience uremic poisoning which can be life threatening.

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Abb. GGTEIIJA: Schematic illustration of the canine male urinary and reproductive organs.
The male urethra, which carries urine from the bladder through the penis to the outside, is very long and narrow.

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Abb. GGTELAHP: Schematic illustration of the canine female urinary and reproductive organs.
The female urethra, which carries urine from the bladder to the vaginal opening, is very short.

Causes

There are several causes of bladder stones in dogs. These include:

  • Chronic urinary tract infections (bladder infections)
  • Breed predisposition such as Bichon Frise, Dalmatian, Yorkshire Terrier, Shih Tzu, Miniature Schnauzer
  • Metabolic disease such as Cushing’s disease
  • Hypercalcemia (high blood levels of calcium)
  • Liver disease
  • Diets high in oxalates such as leafy green vegetables or nuts
  • Diet high in minerals
  • Diets which cause acidic urine

Cardinal symptom

  • Straining to urinate
  • Hematuria (bloody urine)

Symptoms

Clinical signs include straining to urinate, hematuria, painful urination, inability to urinate, and increased frequency of urination. In cases of urinary obstruction, loss of appetite, abdominal pain, vomiting and depression can be seen.

Diagnosis

A presumptive diagnosis can be made from the history and physical examination. Some stones in the bladder can be palpated (felt) on physical examination. If bladder stones are suspected, radiographs should be obtained. Most stones are visible on radiographs. Ultrasonography can also be used to examine the bladder for bladder stones and chronic thickening.

A urinalysis is a diagnostic test performed to analyze the urine. This test consists of two parts: the first examines different properties of the urine such as pH, specific gravity (concentration), amount of protein, blood, glucose, ketones and other biochemicals. This is performed by using a special reagent strip dipped in the urine. The second part of the urinalysis involves examining the sample under the microscope for abnormal cells, bacteria and crystals. A urinalysis is used to identify urinary tract stones and aid with proper treatment. A complete blood count (CBC) and serum biochemistry and electrolyte panel may be necessary in cases of urinary tract obstruction to determine the health of the kidneys.

If bladder stones are surgically removed or if they are passed in the urine and recovered, it is important that they are analyzed to determine the mineral content. Knowing the composition of the stones will aid in determining a cause, treatment and prevention.

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Abb. GGNIF898: Bladder stones.
This is a radiograph of a dog with bladder stones of different sizes.

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Abb. GSSKW0F1: Bladder stone.
This is an image of a bladder stone as seen with ultrasonography.

Treatment

If stones are diagnosed in the urinary tract and the dog is not obstructed, treatment will depend on the patient, the type of stones suspected, the location of the stones and the size of the stones.

The three methods of treating urinary stones are:

Dissolving by feeding a specially formulated, prescription diet: Some stones will dissolve when the dog is fed a special diet. While this treatment is non-invasive, it can take 3-4 months to dissolve stones. Antibiotics should also be given during this time to prevent urinary tract infection. With this treatment, the dog is still at risk for developing a urinary obstruction.

Flushing the bladder with a urinary catheter ( voiding urohydropropulsion ): If stones are small enough to pass, a urinary catheter can be passed into the bladder and the bladder filled with a sterile solution. The bladder can be agitated so the stones float freely then pressure applied to the bladder to force the stones out. This procedure is best performed under sedation and can still result in some stones being left in the bladder or urethra. Any stones retrieved from this procedure should be analyzed for composition.

Surgical removal ( cystotomy , urethrotomy ): Surgical removal of bladder and urethral stones is the most direct method of treatment and provides immediate relief from pain and irritation. However, surgical removal is invasive and some dogs may not be good candidates for surgery. Stones removed from surgery should be analyzed for composition.

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Abb. GGNIUU49: Bladder Stones.
This is a photograph of surgically removed bladder stones. Bladder stones can be different sizes and shapes depending on the composition.

If a dog is obstructed from a urethral stone, this is a medical emergency and the obstruction must be removed. A urinary catheter can be passed in hopes of pushing the stone back into the bladder to allow urine to be voided. The catheter may be left in place until surgical removal can be performed. In the case of an obstruction, intravenous fluids, antibiotics, antispasmodics and pain medication may be needed to stabilize the dog before surgery.

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Abb. GGNIXXJQ: Urinary Catheters.
This is photograph of a urinary catheter used to treat urinary tract obstructions.

Prognosis

Dogs with urinary tract stones which are not obstructed have a good prognosis for recovery. Surgical removal is usually successful with minimal complications. However, dogs which are obstructed may have permanent kidney damage and life-threatening complications. Also, certain types of stones have a higher incidence of recurrence. Preventing these recurrences can be difficult and frustrating. Dogs may need repeat surgeries which can be costly and result in scarring to the urinary tract.

Prevention

Depending on the type of bladder stone recovered from the dog, a specially formulated prescription diet, dietary restrictions or antibiotics may be necessary to prevent recurrence.

Male dogs which continue to form bladder stones and become obstructed may benefit from a surgical procedure called a urethrostomy where a permanent urinary opening is created in the urethra in the scrotum area.

Update version: 4/24/2014, © Copyright by www.enpevet.de
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