Urinary Calculi – Stones that really can hurt

Urinary Calculi –
Stones that really can hurt

By Dr. Ed Mapes
Stonebridge Animal Hospital
McKinney, Tx.

Stones that form in the urinary tract are called uroliths or calculi. They form when minerals present in the urine crystallize. Under the right conditions, the crystals coalesce to form the actual stones. This can occur in most breeds of dogs and cats, but some are particularly susceptible.
The stones usually develop in the kidneys or urinary bladder, and lead to serious situations if they become lodged within the ureters or urethra, where they obstruct urinary flow. (Figure1). This is the biggest danger posed by the presence of urinary stones – obstructed urine flow causes serious damage to the kidneys. Waste products normally excreted in urine accumulate in the bloodstream, causing damage to other cells and tissues in the body. This process can prove fatal within a matter of two or three days, and animals that cannot pass urine should be seen by a veterinarian immediately.

Figure 1: Accumulation of small stones in a dog’s urethra

Figure 1: Accumulation of small stones in a dog’s urethra

Figure 1 the accumulation of small stones in this dog’s urethra have obstructed urine flow and created an emergency situation. I removed the stones at surgery, but damage to the urethra called for creating a new orifice through which to pass urine.

It is rarely obvious that a patient has urinary stones; we usually see animals presented for complaints of urinating outside the litter pan, straining to urinate, producing only small amounts of urine at a time, or having blood-tinged urine. Sometimes the patients seem painful, especially in the abdomen, and lose their appetite or begin to vomit. We often make a presumptive diagnosis of urinary calculi by examining the patient – we can actually feel (palpate) the stones within the urinary bladder. X-rays (Figure 2) often confirm our suspicions, but special techniques – contrast or double contrast radiograms – are sometimes needed. We can also inject a dye solution into the blood stream and X-ray the urinary system as it passes into the urine.

Figure 2:  Radiograph confirmed suspicions – there are many stones in this dog’s bladder.

Figure 2: Radiograph confirmed suspicions – there are many stones in this dog’s bladder.

Stone formation can occur slowly, sometimes over a period of years, with the animal demonstrating very few symptoms of urinary disease even though the bladder is usually painful. The most common uroliths, known as struvite stones (Figure 3), are often seen in female dogs with bladder infections and alkaline urine. These patients usually show some of the symptoms mentioned earlier, but the signs can be subtle.

Figure 3: Struvite stones surgically removed from a dog’s bladder

Figure 3: Struvite stones surgically removed from a dog’s bladder

Struvite stones are comprised of magnesium, ammonium, and phosphate ions, and form when the bladder is infected with bacteria that breaks urea down into ammonia. Ammonia is toxic to the cells of the bladder wall and causes inflammation. Substances released in the inflammatory reaction causes the formation of crystals that eventually coalesce to form actual stones.
Bladder infections can be complicated by a congenital malformation of the urinary bladder known as the urachal diverticulum. This blind pouch that develops in the bladder wall becomes the focal point of infection, leading to repeated infections that can further stone development.
Other stones form independent of infection due to abnormalities in the animal’s metabolism of proteins or minerals within the urine. Calcium oxalate stones are a good example. These nasty little stones are usually sharp-edged, and contribute to pain in the bladder. They can be especially difficult to remove if they pass into the urethra, where the jagged edges adhere to the lining. They often occur in cats without bladder infections and more acid urine.

As these examples illustrate, urinary stones develop for a variety of reasons in different animals; there is no single preventative measure effective in all cases. In some cases, dietary changes can decrease the minerals responsible for stone formation, and actually –over a period of months – decrease the size of stones. The danger of obstruction exists though, throughout the trial period, and is a constant concern. I’ve had very little luck with this method. Another method of treatment is by disruption of the stones (lithotripsy) using laser beams or shock wave therapy. These methods, adapted from human medicine, are only available at specialty centers or universities, and can be attempted on larger canine patients with urethras big enough to accommodate the instruments.

In my experience, surgical removal of the stones is usually the most effective and immediate means of removing the stones, flushing the urethra to prevent obstruction, and often correcting a urachal diverticulum if present. Samples of the calculi are then sent to the laboratory for analysis, which guides us in making recommendations for future prevention. This can include changing to specially-formulated diets, preventing recurrence of infection, altering urine pH, or prescribing specific medications to manage metabolic abnormalities. I like the immediacy of removing the stones to prevent the possibility of urinary obstruction, which is a constant threat whenever attempting dissolution with diet changes. Surgery is also the only means of correcting a diverticulum.

Please don’t hesitate to have any animal with signs of a possible urinary problem seen by a veterinarian. There could be a reason for the pink urine or loss of house training, one that could spell real trouble if left uncorrected. Refer to a previous article, The wagging tail that saved Angel’s life, for a great example of what I mean.

Comments are closed.