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Bladder Stones

Randy Walker DVM

About Bladder Stones...

Bladder stones occur in both dogs and cats and are composed of various minerals. Types of bladder stones include struvite stones (also called magnesium-ammonium-phosphate stones, MAP stones, or triple phosphate stones), calcium oxalate stones and urate stones among others. (See the normal Urinary Bladder).

How Do Bladder Stones Form?

Bladder stones begin when crystals in the urine condense. These crystals can arise from a shift in the metabolism of the individual or secondary to a bacterial infection or both.

Which Stones Are Most Common?

In dogs and cats, struvite stones account for about 90% of the stones seen. The remaining 10% are mainly calcium oxalate stones. Urate stones and the others make up the rest of stones seen.

How Do Urinary Stones Compare Between Animals And Humans?

In humans about 90% of the urinary stones occur in the kidneys (kidney stones) while about 10% occur in the bladder (bladder stones). In animals these proportions are reversed with 90% of the urinary stones occurring in the bladder and 10% in the kidneys.

How Are Bladder Stones Diagnosed?

Bladder stones and crystals are diagnosed by several means. Often (but not always) the crystals that make up bladder stones will be detected on the routine urinalysis. Often (but not always) bladder stones can be palpated (meaning to feel diagnostically with the fingers) in the bladder. Radiographs are essential to properly diagnose bladder stones since it is very important to make sure that no stones are located in the kidneys and ureters as well as the bladder. Also, one type of bladder stone (the urate stone) does not show up well on conventional radiographs so a special technique (called contrast radiography) is used for these radiographs when these stones are suspected. It is also important that all stones retrieved from the body be sent to the laboratory for a complete analysis.

Why Is It Important That The Stones Be Analyzed?

This is because we have a different therapy for each type of stone and this therapy needs to be followed precisely in order to achieve a successful outcome. Although we can sometimes get an idea of the type of stone from its general appearance, many stones are composed of two or more types of minerals and the treatment for these must be tailored to the individual case.

How Are Bladder Stones Treated?

Bladder stones are treated by two main methods: (1) surgical removal and (2) medical and dietary therapy.

Briefly, How Are Bladder Stones Treated By Surgical Removal?

First the patient is placed under a light general gas anesthesia. Then an incision is made through the abdomen and the bladder is located. Next, an incision is made through the bladder wall and the bladder stones are removed and saved for analysis. Then the incision in the bladder wall is repaired followed by closure of the body wall itself. When the patient is awake and mobile they are free to go home. When stones are removed surgically, antibiotics are used both before and after surgery along with a low mineral/low pH diet to help dissolve the crystals that are present.

Briefly, How Are Bladder Stones Treated By Medical & Dietary Therapy?

It should be noted that medical and dietary therapy works only for struvite stones and not for other types of stones. When struvite stones are treated this way the patient is placed on a special dog food (usually Hill's Canine s/d) which is low in the types of minerals which produce stones (magnesium and phosphorous) and which also gives an acid pH to the urine. Struvite stones will dissolve in a low pH (acidic) urine. Also, antibiotics are begun and continued until the stones are completely dissolved (sometimes over 6 weeks) because bacteria get trapped within the stone as it is formed and these bacteria are released as the stone dissolves. Radiographs are taken periodically to monitor the progress, as the stones decrease in size.

Which Type Of Therapy Do You Prefer For Elimination Of Stones?

I personally prefer surgical removal of bladder stones for several reasons. The main reason is because this allows us to perform a complete analysis of the stones. This is very important in formulating a plan to prevent the stones from reoccurring. Medical and dietary therapy (also known as dissolution therapy) is effective only for struvite stones and will not work for other types of stones. Also it should be noted that sometimes a patient can aquire one type of stone (such as calcium oxalate stones) and then get a bacterial infection of the bladder secondarily and this leads to struvite formation. In this case the struvite will be laid down over the calcium oxalate resulting in stones and these will look like struvite stones and struvite crystals will be present in the urine. If a patient with this type of stone (calcium oxalate surrounded by layers of struvite) is placed on medical and dietary therapy the stones will dissolve until only the core of calcium oxalate remains and then the stone will stop dissolving. In these cases the remaining stones will need to be surgically removed anyway. Also if the patient has the type of metabolism that makes calcium oxalate stones, then medical and dietary therapy for dissolving struvite stones could make the problem worse. These are some of the reasons why surgical therapy is preferred for most cases of bladder stones.

How Are Bladder Stones Prevented?

In vast majority of cases recurrence of stones can be prevented by placing the patient on a special diet which is low in the types of minerals that produce their particular type of stones (such as a diet low in magnesium and phosphorus to prevent struvite stones) and also a diet which promotes the type of urine pH that prevents formation of the particular types of crystals that this patient's body forms (an acid pH for struvite crystals or a basic pH for calcium oxalate crystals).

What Is The Prognosis For Future Stone Prevention After The Stones Have Been Eliminated?

When the proper special diet (such as Hill's s/d & c/d for struvite stones and Hill's u/d for calcium oxalate stones) is strictly adhered to we estimate that stones will not return in over 90% of cases. If the special diet is not strictly adhered to, the chances are over 80% that the stones will return.

What Happens If The Stones Return After Having Been Eliminated?

If the stones return then we are back to square one and again have to make the decision as to treat them and carry out that treatment. We certainly have had to remove stones twice when the special diet was not adhered to.

- Randy Walker DVM
Sun Lakes Animal Clinic
May 14,2004