Affects: Cats, Dogs
Bladder stones or uroliths are a common occurrence in animals, especially in domestic animals such as dogs and cats. Occurrence in other species, including tortoises, has been reported as well. The stones form in the urinary bladder in varying size and numbers secondary to infection, dietary influences, and genetics. Stones can form in any part of the urinary tract in dogs and cats, but unlike in humans, stones of the kidney are less common and do not often cause significant disease, although they can contribute to pyelonephritis and chronic kidney disease. Types of stones include struvite, calcium oxalate, urate, cystine, calcium phosphate, and silicate. Struvite and calcium oxalate stones are by far the most common. Bladder stones are not the same as bladder crystals but if the crystals coalesce unchecked in the bladder they can become stones.
Signs And Symptoms: Bladder stones may cause blood in the urine (hematuria) but sometimes there may be no signs at all. Painful urination or straining to urinate are other signs. Urinary tract infections are commonly associated with bladder stones. Smaller stones may become lodged in the urethra, especially in male animals, causing urinary tract obstruction and the inability to urinate. This condition causes acute kidney failure, hyperkalemia, sepsis, and death within a few days.
Diagnosis: When symptoms indicate bladder stones, the first step is usually to take an x-ray. Most types of stones will appear readily in an x-ray, urate and occasionally cystine stones being the most common exceptions. Stones smaller than three millimeters may not be visible. Ultrasonography is also useful for identifying bladder stones. Crystals identified in a urinalysis may help identify the stones, but analysis of the stones is necessary for identification of the complete chemical composition.
Treatment: Reasons for treatment of bladder stones include recurring symptoms and risk of urinary tract obstruction. Some stones, including struvite and urate stones, can be dissolved using dietary modifications and/or medications. Calcium oxalate stones are insoluble and must be surgically removed. Small stones in female dogs may possibly be removed by urohydropropulsion, a nonsurgical procedure. Urohydropropulsion is performed under sedation by filling the bladder with saline through a catheter, holding the dog vertically, and squeezing the bladder to expel the stones through the urethra. Bladder stones can be removed surgically by a cystotomy, which is a small incision into the bladder to scoop out the stones. Stones lodged in the urethra can often be flushed into the bladder and removed, but sometimes a urethrotomy is necessary. In male dogs with recurrent urinary tract obstruction a scrotal urethrostomy creates a permanent opening in the urethra proximal to the area where most stones lodge, behind the os penis. In male cats, stones lodge where the urethra narrows in the penis. Recurrent cases can be treated surgically with a perineal urethrostomy, which removes the penis and creates a new opening for the urethra.
To prevent recurrence of stones, special diets can be used for each type of stone. Increasing water consumption by the animal dilutes the urine, which prevents oversaturation of the urine with crystals.