Monday, June 8, 2015

Bladder stones and stone removal surgery (cystotomy), a cat-owner's guide to what to expect

Two stones in the bladder of a cat

What is a bladder stone?

A bladder stone is a rock-like accumulation of minerals that forms in the bladder. Some stones stay small and others can become quite large. Sometimes, a cat may have a few stones of varying sizes, or a large number of stones that appear to be like gravel. Sometimes, a cat may have urinary crystals or a bladder infection that precedes the formation of the stone. Other times, a bladder stone may be a "silent problem" and be diagnosed incidentally when the cat is being examined for other issues.

Bladder stones are also called "urinary calculi" or "uroliths", and the condition of having bladder stones is called "urolithiasis". In addition to forming stones in the bladder, a cat may form stones in the kidneys or the ureters (the tubes that connect the kidneys to the bladder). If a stone passes out of the bladder and becomes lodged in the urethra (the tube that connects the bladder to the outside of the cat), the urine flow may become obstructed and develop into a life-threatening emergency.

Bladder stones usually take weeks or months to form.

There are a number of types of stones that can form in the bladder of cats, but the two most common types are struvite stones (also known as magnesium-ammonium-phosphate stones, or "triple phosphate stones") and calcium oxalate stones.  According to the Minnesota Urolith Center, in 2006, 50% of the stones found in cats were struvite and 39% were calcium oxalate. The remaining 11% were a variety of other stones.

What causes bladder stones in cats?

Stones come in many colors, shapes and sizes!
 No single cause of bladder stones has been identified in cats. Stone formation appears to be related to a variety of factors, including environment, inter-cat relations, diet, eating habits, age, breed, water intake, genetics, litterbox husbandry, and current medications.

When the urine has a lot of "stuff" in it (body waste products, proteins, salts, etc.), that "stuff" settles out of solution and begins to bond together. Even a normal urine sample begins to form crystals when it is allowed to sit for long periods. As the water portion of the urine evaporates, more and more of the "stuff" is left behind, and the urine becomes more concentrated, this is called supersaturation, and is considered to be the leading factor in bladder stone and crystal formation (ThePrecipitation-Crystallization theory). This can happen for a variety of reasons:

  • insufficient water intake
  • infrequent visits to the litter to empty the bladder
  • increased intake or body production of the components that make up urinary stones and crystals (such as magnesium, ammonia, phosphate, calcium...)

Of cats that have had calcium oxalate stones, there is a possible breed pre-disposition among Burmese, Himalayan and Persian cats.  Neutered males of all breeds are at 1.5 times higher risk for calcium oxalate stone formation than females.

Breeds at higher risk for feline struvite urolithiasis as reported by the Minnesota Urolith Center include the Foreign Shorthair, Ragdoll, Chartreux, Oriental Shorthair, Domestic Shorthair and Himalayan. The Rex, Burmese, Abyssinian, Russian Blue, Birman, Siamese and mixed-breed cats had a significantly lower risk of developing struvite uroliths. At the California laboratory, Himalayan and Persian cats had a higher risk for struvite stones compared with their expected breed frequency.

In dogs and humans, struvite stone formation is usually associated with a urinary tract infection, however in cats, 80-95% of cat with struvite stones have sterile urine (no bacterial growth).

Urine pH appears to have a significant effect on stone formation. Oxalate stones form in neutral to acid urine (pH of 7 or less), struvites form in neutral to alkaline urine (pH of 7 or more).

Cats that form struvite stones tend to be younger cats.
Cats that form oxalate stones tend to be middle-aged to older cats.

About one-third of cats with calcium oxalate bladder stones have elevated blood calcium (hypercalcemia).  Calcium oxalate formation may be related to hyperparathyroidism or idiopathic hypercalcemia.

What are the symptoms of bladder stones?

               Changes in litterbox behavior including:
  • straining to urinate
  • urinating small amounts
  • vocalizing while urinating
  • inability to produce urine
  • frequenting the litterbox (with or without producing urine)
  • eliminating outside the litterbox
  • change in posture in the litterbox

Other signs:
  • blood in the urine
  • licking at the lower abdomen frequently (with or without hair loss)
  • licking genitals frequently
  • painful abdomen
Many of these signs are general signs of any urinary disease or condition. About 25% of cats with signs of urinary tract disease have stones, so it is good practice to check any cat that presents with urinary complaints, to avoid missing a stone and leave the cat at risk for obstruction.

How are bladder stones diagnosed?

         Radiography or ultrasound studies are the most effective way to diagnose a bladder stone. In
Ultrasound image: One large stone in a cat bladder
some cases, we identify bladder stones when taking an x-ray for an entirely different reason. Some
stones are more likely to be seen on an x-ray than others. Calcium oxalate stones are much more visible on x-ray than struvite stones (about 80% of cases involving oxalate stones can be seen on x-ray). Struvite visibility is dependent on how much calcium phosphate is contained in the stone. Urate stones are poorly visible on x-ray, and urohemoliths (stones that form from blood) are not visible on x-ray or ultrasound at all. In some cases, a special dye may be passed into the bladder through a catheter in order to try to visualize radiolucent stones (stones that do not show up on x-ray). This technique is called double-contrast cystography.

How are bladder stones treated?

Dietary change

Special crystal and stone-dissolving diets, and crystal/stone prevention diets can be fed to attempt to dissolve the stones, however, once formed stones made of calcium oxalate will not dissolve. If this course of treatment is chosen, the cat must not eat any other food but the dissolving diet, or it will slow the dissolution of the stone. It may take several months to dissolve struvite stones. Typically, if a stone-dissolving diet is being fed, x-rays should be taken every 3-4 weeks to ensure that the stone is getting smaller. If the stone does not appear to be dissolving, then surgical removal would be the next step. It is not advisable to feed a diet that simply restricts magnesium or phosphorous intake, as magnesium is an inhibitor of Calcium Oxalate stone formation, and decreased phosphorous may cause the body to absorb more calcium, placing the cat at higher risk for calcium oxalate stones.Urine pH appears to be a more important factor in stone formation than mineral content of food.

Dietary supplements or other medications

 If dietary change is not effective, oral supplements may be given to assist in changing the urine pH enough to prevent the formation of the offending stones. These supplements include thiazide diuretics, Vitamin B-6,  potassium citrate for oxalate stones and methionine and ammonium chloride for struvite stones.

Surgery (cystotomy)

Under general anesthesia, an incision is made into the abdomen and then into the bladder to remove the stones. The bladder is flushed with sterile saline to ensure the removal of all stones and debris. The abdomen is closed and a post-surgical x-ray or ultrasound is performed (depending on how the stones were diagnosed) to ensure that all stones have been removed. The stones are then sent to a reference laboratory for analysis. Bladder stones of similar makeup can look different, so it is important to identify the stones to determine the correct treatment. Recovery is usually 24 hours, but some cats may be uncomfortable post-surgery and have blood in the urine or may continue to strain in the litterbox until the bladder is healed.

Retrieval of the stones through manual expression  

The veterinarian gently compresses the bladder while the cat is under anesthesia, and the stream of urine carries the stones with it. This can only be done if the stones are small - <5mm in females and <1mm in males. This is called "urohydropropulsion". If this is performed on a cat with larger stones, the stones can become lodged in the urethra and cause an obstruction. At that point, steps must be taken to un-obstruct the cat, and then surgical removal of the stones should be performed so that the cat does not re-obstruct while trying to urinate.

Cystoscopy retrieval

If the urethra is large enough in a female cat, the stones can be "fished up" in a special instrument and crushed to allow them to be expressed. This procedure is generally only performed at university veterinary hospitals as it requires special expertise. 

Encourage water intake

 Offer fresh water in multiple locations in the home. Water fountains may be more attractive than a plain dish. Additionally, feeding only canned food (no dry kibble) will add moisture to the diet, as canned foods contain 70-80% moisture. Increased water content dilutes the urine, preventing the urine from becoming supersaturated. Cats with idiopathic urinary tract disease that ate a high-mosture-containing diet (wet food) had a recurrence rate that was 1/2 that of cats eating a dry food diet.


This procedure involves shock waves generated either within the bladder or outside of the body to break up the stones. This requires special equipment and expertise, so is not generally available. This treatment is only available for female cats as it involves the use of a cystoscope which is too large to place in a male cat's urethra. This procedure is offered at the following universities: The University of California Veterinary School in Davis, The University of Minnesota Veterinary School , Minnesota Urolith Center, the Veterinary School at Purdue University, the Cummings School of Veterinary Medicine at Tufts. It is also performed at the veterinary school in Montreal and Guelph, the Animal Medical Center (AMC) in New York, and the University of Tennessee. Cost for this type of procedure is $1500-7000.


If stones are present along with a urinary tract infection, antibiotics should be given to treat the infection. Sometimes, a stone can be a source of infection, if bacteria are embedded within, so an infection that is not responsive to an appropriate antibiotic (determined by performing a culture and sensitivity test) may require that the stone be removed before completing antibiotic treatment.

What is the prognosis for my cat after treatment?
Three reports from Minnesota Urolith Center: It has been a busy month for bladder stones!

Many cats that develop stones will be at a high risk for recurrent issues, even with preventive care. This is why is is important to follow-up with your veterinarian on a regular schedule.

>20% recurrence of struvite stones
25-48% recurrence of calcium oxalate stones

What if I choose not to treat my cat for bladder stones?

Chronic inappropriate urination, urinary obstruction which results in an emergency situation that could become fatal. Signs of a urinary blockage include - poor appetite, vomiting, nausea, firm, painful and distended abdomen, and other signs similar to the presence of urinary stones.

How can I prevent bladder stones?

  • If your cat has elevated calcium levels, followup should be done to identify whether it is idiopathic hypercalcemia or hyperparathyroid disease, and treatment should be performed.
  • Feed canned food daily (3-6oz)  - Canned food is 80% water and will increase a cat's hydration level, encouraging urine output, encouraging more freuqent trips to the litterbox, preventing urine from remaining in the bladder for long periods of time.
  • Encourage water consumption -this results in more dilute urine which prevents crystals and stones from forming. We aim for a urine concentration below 1.030.
  • Offer a sufficient number of litterboxes for your cat population and clean them at least once daily (Read more about litterboxes) - Even if a cat is not urinating outside the litterbox, if the cat is not fully satisfied with the box, he may choose to urinate less frequently. This allows urine to sit in the bladder for longer, allowing more time for minerals to settle out of the urine and bond together into crystals and stones.
  • Your vet will likely recommend periodic rechecks - urinalysis, x-ray or ultrasound, depending on how the stones were diagnosed. It is highly recommended to abide by these recommendations, so that you can take steps to treat your cat before it becomes necessary for surgical stone removal (cystotomy).
  • If your cat is prone to calcium oxalate stones, medications such as prednisolone, lasix, dexamethasone, and Vitamin C should be used with caution.

Are bladder stones a sign of a larger problem?

In some cases, yes.

Hyperthyroid disease and diabetes place cats at higher risk for urinary tract infections which, in turn, can be associated with stone formation. If your cat is in a risk category for these diseases and develops a stone, your vet may recommend blood testing to rule out other diseases.

Cats with high levels of calcium may have no known cause ("idiopathic hypercalcemia"), or may have an underlying disorder such as hyperparathyroidism, Cushing's disease or certain types of cancer.

Cats that form urate stones may have a congenital portal-systemic shunt.

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