Uroliths are urinary tract stones that can be found in the kidney, ureters (the tube between kidneys and bladder), bladder, and urethra (tube between bladder and urinary system opening). The presence of these stones can cause many symptoms. Lower urinary tract stones (urocystolithiasis) is one of the conditions placed under the umbrella of the Feline Lower Urinary Tract Disease (FLUTD) complex.
A diagnosis of urocystolithiasis is made by performing a urinalysis (analyzing a urine sample). Imaging studies such as X-rays, and sometimes ultrasound of the abdomen are frequently carried out.
Usually the presence of urinary stones is obvious on an X-ray, and the number and location of the stones can be noted. Most stones are comprised of either magnesium ammonium phosphate (MAP, struvite) or calcium oxalate. Historically, struvite stones were the primary type of stone encountered. However, when commercial feline diets were developed which produced more acidic urine, the percentage of struvite stones started to decrease and calcium oxalate stones became more prevalent. These days, the frequency of both is dropping due to new diet formulations.
The type of stone will be taken into consideration when developing a treatment plan. Struvite stones in the bladder can sometimes be treated medically by special diets that are designed to dissolve the stones slowly over time (i.e. Hill’s Science Diet ® Prescription s/d). However, bladder irritation is caused by stones, and this continues while they are dissolving. There is also a small risk of stones traveling down into the urethra with the urine, and lodging there causing a blockage. Usually dietary management is attempted when the stones are fairly small. All other types of stones, and sometimes struvite ones must be removed surgically by a cystotomy (surgical incision into the bladder). Once the stones are removed, the cat is placed on a maintenance prescription diet to prevent recurrence of the urocystolithiasis.
Stones of the urinary tract are quite common and some important preventive factors that have been identified include feeding canned food that produces a moderate acidity, increasing water consumption, avoiding obesity, and reducing stress.