Bladder stones are abnormal accumulations of minerals and other substances in the urinary bladder that congregate to form what we commonly refer to as "stones." Stones usually occur in the hollow organs of the body or in their passages, such as the urinary bladder, kidneys, gall bladder, ureters or urethra. These stones are generically called "calculi." When they are in the urinary tract, they are called "uroliths." For our articles, we will just call them stones, as they can be formed in the kidneys, bladder, gall bladder or elsewhere. Stones can occur in any part of the urinary tract, from the kidneys to the ureters to the urinary bladder and ultimately to the urethra. They become problematic when they obstruct the ureters (the passages between the two kidneys and the urinary bladder) or the urethra (the single passage from the urinary bladder to the outside world). When this happens, the stones block the normal outflow of urine – a condition that is extremely painful and can rapidly become life-threatening if not treated immediately. In dogs, urinary stones are most commonly formed in the bladder and then become stuck in the urethra.
Causes of Bladder Stones in Dogs
Canine urine contains a number of different minerals, or salts, that normally remain dissolved in fluid. When the urine becomes too concentrated, or "supersaturated," these dissolved salts can precipitate out of the fluid to form solids in the form of crystals. These crystals can damage the lining of the urinary tract, causing blood in the urine (hematuria), and can predispose affected dogs to developing bacterial urinary tract infections. Over time, the mineral crystals can aggregate with organic material (which can include bacteria) and coalesce to form calculi, or what commonly are called stones. When calculi form in any part of the urinary tract, they are referred to as uroliths. For the purpose of our articles, we are going to refer to calculi, and uroliths, as stones. The pH of urine contributes to stone formation. Some crystals form in urine that has a high pH (alkaline urine), while others form in acidic urine, which has a low pH. Urine pH can be affected by a number of things, including diet, hydration, the presence of bacteria/urinary tract infections, certain medications, conformation of urinary tract structures and genetics. Common types of urinary tract crystals and stones are struvite (magnesium ammonium phosphate), calcium oxalate, urate, calcium phosphate, silicate and cystine. The crystals can accumulate to form one stone, many stones, small stones or very large stones, and the surface of these stones can range from smooth to jagged.
Prevention of Bladder Stones
Any obstruction of the canine urinary tract is potentially fatal. A well-balanced, high-quality diet can promote urinary tract health. Annual veterinary check-ups, including routine blood work and urinalyses, can help veterinarians detect abnormal levels of crystals in the urine well before they become symptomatic or form stones. Once detected and removed, stones are best prevented (or at least managed) by dietary changes, including a protein-restricted diet. There are a number of good, commercially available diets to address problems with stone formation and other urinary tract problems. It is also important to keep dogs well-hydrated, because dehydration increases the concentration of canine urine and predisposes the dog to developing crystals and urinary stones.
Urinary tract infections predispose dogs to development of stones in their urinary tracts. The reverse is true as well, underscoring the importance of annual veterinary examinations accompanied by urinalyses and routine blood screening for our companion animals.
The symptoms of bladder stones in dogs depend largely on the type, number and location of the stones within the urinary tract structures. When stones form and cause a partial or complete blockage of urine outflow, clinical signs quickly develop and rapidly worsen.
Symptoms of Bladder Stones in Dogs
Many affected dogs show no outward signs of discomfort from urinary tract crystals or stones. The signs become obvious when the crystals damage the urinary tract lining, or when one or more stones block the ureters or urethra, causing acute and extreme pain and predisposing the dog to bladder rupture, which is a very serious condition. Signs that owners might notice of urinary tract stones include:
Blood in the dog's urine (hematuria). This is an early symptom, caused by physical disruption of the bladder lining
Increased frequency of urination or attempts at urination. When a physical blockage occurs, the symptoms worsen dramatically and rapidly, and the dog will urinate (or try to urinate) much more frequently than usual, although those attempts will not be very productive
Straining to urinate (this may look like straining to defecate), without much success
Incomplete voiding (urinary retention)
Agitation (affected dogs are extremely painful and typically become frantic, developing a pleading, helpless look)
Repeatedly turning and looking at the abdomen and hindquarters
Running to and from the normal "pottying" place
Inappropriate elimination (pottying in unusual or inappropriate areas – in the house, on the bed, etc.)
Lack of appetite (anorexia; inappetance)
Many of these signs mimic those of other conditions, such as urinary tract infections and bloat (gastric dilatation and volvulus). It is very important to get a dog displaying a number of these symptoms to a veterinarian as quickly as possible, as all of these conditions are very serious.
Dogs at Increased Risk
Stones in the urinary tract are more common in older animals and in males, although they have been reported in dogs of both genders and of all ages. Several breeds are overrepresented in the population of dogs that develop urinary stones, depending on their composition:
Struvite (magnesium ammonium phosphate): Miniature Schnauzer, Bichon Frise, Cocker Spaniel, Miniature Poodle. A very common canine stone, especially in females and dogs under one year of age. Commonly associated with urinary tract infections.
Calcium oxalate: Miniature Schnauzer, Miniature Poodle, Yorkshire Terrier, Bichon Frise, Lhasa Apso, Cairn Terrier, Shih Tzu. The most common canine stone. Obesity puts dogs at increased risk.
Urate: Dalmatian, English Bulldog, Yorkshire Terrier, Miniature Schnauzer. An uncommon canine stone.
Silicate: Miniature Schnauzer, German Shepherd, Golden Retriever, Labrador Retriever, Old English Sheepdog, Cocker Spaniel. A very uncommon canine stone.
Cystine: Dachshund, English Bulldog, Bassett Hound, Yorkshire Terrier, Irish Terrier, Rottweiler, Chihuahua, Tibetan Spaniel, Mastiff, Newfoundland. A very uncommon canine stone.
Fortunately, urinary tract stones (medically called uroliths) are not especially difficult to diagnose in domestic dogs. The key factor is getting affected dogs to a veterinarian as quickly as possible, to avoid bladder rupture or the other potentially life-threatening consequences of urinary tract blockage.
How Bladder Stones Are Diagnosed
Canine stones somewhere in the urinary tract are typically diagnosed based upon the dog's history as told by the owner, a complete physical examination, a urinalysis and abdominal radiographs (x-rays). Urine culture and sensitivity are useful where bacterial infection is suspected. Abdominal ultrasonography can also be helpful in arriving at a diagnosis. Another diagnostic tool available to veterinarians, especially in male dogs suspected of having a urinary blockage, is attempted passage of a urinary catheter through the urethra. In cases of partial or complete obstruction caused by a stone, there will be obvious resistance, which some authorities have described as having a "gritty" feeling. Advanced tests that can usually confirm the diagnosis also include retrograde positive contrast-enhanced urethrography, double-contrast-enhanced cystography and cycstoscopy (use of a scope to visualize and sample stones in the bladder). The attending veterinarian can discuss these specialized procedures in more detail and may refer the owner to an internal medicine specialist, if these advanced tests are unavailable in the local clinic.
In most cases, advanced diagnostic procedures are not done until the dog shows symptoms that suggest urinary tract blockage or a urinary tract infection. If your dog exhibits these signs, please take her to your veterinarian as soon as possible.
Bladder stones in dogs are usually asymptomatic until they move down the urinary tract and become lodged in the urethra. When this happens, the dog will quickly become painful and will attempt to urinate more frequently than normal and will show signs of straining when trying to potty, among other symptoms. Urinary tract obstruction is an extremely serious condition that can lead to rupture of the bladder, and ultimately to death. It is a true medical emergency. The goals of treating this condition are to remove the stones and the blockage, resolve any urinary tract infection and prevent additional stones from forming.
Depending upon their composition, stones in the urinary tract can be either dissolved with diet and medical management or removed surgically. The best treatment option is to detect and remove the stones before they cause a physical blockage. Once obstruction occurs, mechanical removal of stones is almost always necessary.
Sometimes, urinary stones can be removed with a nonsurgical procedure called urohydropropulsion. This is more commonly done in female dogs, based on their anatomical differences from males. During this procedure, the dog is sedated, a urinary catheter is inserted into the urethra, saline fluid is flushed through the catheter into the bladder, and then the bladder is squeezed to flush out the stones if possible. Alternatively, abdominal surgery is performed to remove the stones directly from the bladder. Abdominal radiographs will be taken before and after the procedure to determine whether all of the stones were successfully removed. Antibiotics may be appropriate if infection is suspected.
Some stones, particularly cystine stones, can actually be dissolved medically through a protein-restricted diet, administration of dietary supplements to reduce the acidity of the urine and maintenance of good hydration. Administration of a product known as 2-MPG can increase the solubility of cystine stones and prevent their recurrence. There can be side effects from this product; as always, discuss all treatment options thoroughly with your veterinarian.
When a dog has large stones or a large number of stones, it is unlikely that non-surgical options will be successful in removing those stones from the urinary tract. Similarly, in cases of complete blockage, there simply may not be time to try urohydropropulsion. In these cases, traditional surgery is required. The surgical procedure is called a "cystotomy," and it is performed under general anesthesia. The veterinary surgeon will make an incision through the skin and abdominal wall, and then will make a much smaller incision directly into the bladder. She will physically remove the stones and then close the bladder, abdominal tissues and skin with appropriate suture material and techniques. This procedure is normally very successful and is about as invasive as a spay procedure in female dogs.
Once the stones are removed from the bladder or from wherever else they were lodged, they will be sent to a laboratory to determine their actual composition. This information will help the attending veterinarian identify why the stones formed and how they might be prevented in the future. The recurrence of certain types of stones can be reduced by placing the dog on a special diet and ensuring that electrolytes and fluids are well-balanced.
The prognosis for dogs with urinary stones is good as long as the condition is detected and treated appropriately. Dogs with complete blockages obviously have a more guarded prognosis than do those only with crystals in their urine or with stones that remain in the bladder itself. However, in both cases, medical management and surgery are available that can be quite successful in resolving any crisis and regulating the condition for the duration of the dog's life. Recurrence of stones is common.