Definition of Bladder Stones
Bladder stones, medically called uroliths or calculi, are accumulations of minerals and other material in the urinary bladder. Bladder stones can be large or small and can form in bunches or alone.
They can develop in any part of the urinary tract, which includes the kidneys, ureters, bladder and urethra, although most stones in cats seem to occur in the bladder. Bladder stones develop when a cat’s urine becomes over-saturated with microscopic mineral crystals.
Over time, these mineral crystals aggregate with organic material, such as bacteria, pus, mucus, whole blood and/or white blood cells, and coalesce to form hard, stone-like structures, which can be smooth or jagged.
The most common minerals that contribute to bladder stones in cats are struvite (magnesium phosphate) and calcium oxalate. Urate salts, calcium phosphate, silica and cysteine can also be involved.
Causes of Bladder Stones in Cats
The pH of a cat’s urine is one of the most important factors in whether bladder stones will form and, if so, what they will be made of. Urine pH is a measure of the degree to which a cat’s urine is acidic or alkaline.
Technically, pH values refer to the level or concentration of hydrogen ions in a particular solution or substance. For purposes of most cat owners, and in language that most people can understand, the main point is to know that “acidic” urine has a low pH, and “alkaline” urine has a high pH.
A urine pH of 6.8 to 7.0 is considered to be neutral. Struvite bladder stones in cats typically develop in alkaline urine (high pH) that also has a high concentration of magnesium, while calcium oxalate stones tend to form in acidic urine (low pH) with low levels of magnesium.
The pH of a cat’s urine can be affected by a number of things, including diet, hydration, bacterial urinary tract infections, certain medications, structural abnormalities in the urinary tract and/or genetics. Dietary intake of magnesium is especially important to the pH of feline urine.
Symptoms of Bladder Stones in Cats
Some cats with bladder stones show no outward signs of discomfort, although this is uncommon. When stones partially or completely block the exit from the bladder (the bladder sphincter), or plug up anywhere downstream, the cat’s symptoms typically develop quickly and rapidly get worse.
Stones can completely obstruct the cat’s urethra, which is the tube that takes urine from the bladder to the outside world. This is a true medical emergency and a potentially life-threatening condition if left untreated.
Bladder stones predispose affected cats to having recurrent and painful urinary tract infections. They are most common in older male cats, although they have been reported in cats of both genders and all ages and breeds.
The symptoms and signs of bladder stones are the same regardless of their mineral make-up. Owners may notice one or more of the following signs if their cat has bladder stones:
- Frequent and frantic attempts to urinate; may or may not be successful; usually produces little to no urine
- Straining and/or vocalizing while attempting to urinate
- Straining and/or vocalizing while attempting to defecate
- Entering and leaving the litter box more frequently than normal
- Fresh blood in the urine (red or pinkish tinge)
- Urinating in unusual or inappropriate places
- Licking the external genitalia excessively
Treating & Prognossis of Feline Bladder Stones
Any obstruction of a cat’s urinary tract can be fatal. A well-balanced, high quality diet can promote urinary tract health and help reduce the risk of bladder stones. Regular check-ups, including routine blood work (a complete blood count [CBC] and serum chemistry panel), and a urine evaluation (urinalysis), can help the cat’s veterinarian detect bladder stones before they become symptomatic.
Fortunately, these stones are easily diagnosed through radiographs (X-rays) and usually can be dissolved with dietary and medical management or removed surgically.
Treatment options depend on the size and number of stones and their mineral composition. Bladder stones that are smaller than the smallest diameter of the cat’s urethra may be treatable with a non-surgical procedure called “urohydropropulsion” or “catheter-assisted retrograde urethral flushing”.
During this procedure, the cat will be heavily sedated or put under general anesthesia. A sterile catheter will be inserted through its urethra, and a non-irritating solution such as saline will be flushed through the catheter into the urinary bladder.
Then, the veterinarian will manually express the bladder, to (hopefully) flush the stones out through the catheter. The veterinarian normally will take abdominal X-rays (radiographs) both before and after this procedure, so that she can assess whether all of the stones have been successfully removed.
When a cat has large or numerous bladder stones, surgery may be necessary. The surgical procedure is called a cystotomy. During a cystotomy, the cat will be placed under general anesthesia.
The veterinarian will make an incision through the abdominal wall and into the urinary bladder, and will physically scoop out the stones. She will then flush the bladder thoroughly with sterile saline and close up the incisions.
Cystotomies in cats usually are quite successful and have a low risk of post-operative complications. Once the stones are removed, they will be sent to a laboratory for detailed analysis of their composition.
The test results are very important to help the veterinarian come up with an appropriate plan to prevent the cat from developing stones in the future. The recurrence of some types of bladder stones can be prevented by placing the cat on a specialized diet.
For example, cats with struvite stones should be on a diet that is low in magnesium, while cats with calcium oxalate bladder stones should be fed a diet that is higher in magnesium. A veterinarian is the best one to advise owners about their cat’s dietary management.