Although we often call the condition 'bladder stones' its real name is urolithiasis and it refers to finding stones (or calculi) anywhere in the entire urinary tract. The urinary calculi can be found in the kidneys, ureters (tiny tubes that carry urine from the kidneys to the bladder), bladder, or urethra (the tube from the bladder to the outside of the animal). However, in the dog, they are found within the bladder itself over 85% of the time.
Dogs with bladder stones may have blood in their urine and may urinate frequently, passing only small quantities each time. Often, they will strain while urinating, holding their body in the same posture for much longer than normal. However, many affected animals show no signs at all. In less obvious cases, the diagnosis is made or confirmed with abdominal x-rays. If a stone is caught in the ureters or urethra, it can easily obstruct urine flow completely, which leads to a painful death. In these situations, only emergency surgery can save the animal.
Types of bladder stones:
There are several different types of bladder stones, depending on their chemical make-up. The more common struvite stones are composed of magnesium ammonium phosphate. Others are made of calcium oxalate, calcium apatite, cystine, or ammonium urate.
How bladder stones are formed:
All bladder stones, whether they are struvite or any other type, are formed by minerals, which first precipitate out in the urine as individual microscopic crystals. Over time, these crystals unite and small grains of sand are formed. Once these first grains are present, additional precipitation forms on their surface and the tiny specks are gradually built into stones that sometimes reach 3" to 4" in diameter. If this happened only rarely, no harm would be done as they would be flushed out of the body with the urine. In certain animals, however, large quantities of minerals are rapidly formed and clinical urolithiasis develops.
What causes bladder stones?
The process is really quite simple, but what causes it to occur only in certain dogs, cats, or humans? As we understand it today, the factors that bring it about are genetic predisposition, bacterial infections, diet, and urine pH. Any one of these could be solely responsible, but it is usually a combination of any or all of them.