This is an example of a normal cat urinalysis. The pH is acidic, there are no white blood cells (WBC's), red blood cells (RBC's), crystals, or bacteria.

This cat had blood in the urine and a urinary tract infection. There were no calculi in the bladder. Unfortunately there was a malignant cancer in the bladder called a transitional cell carcinoma. Surgery was performed to removed the cancerous portion of the bladder, and so far this cat is doing fine. What we originally thought was a urinary tract infection, with possible cystic calculi, turned out to be a more serious problem. This ultrasound finding and subsequent successful treatment emphasizes the importance of thorough diagnostics.

The following QuickTime video shows a bladder tumor called a transitional cell carcinoma (TCC), that has also spread to the liver unfortunately. Double click on it and in a few seconds it will play. In the beginning, it shows our patient laying on his back in a nice calm and quiet area. We find that if we keep things calm, and the lighting subdued, that these pets do just fine. During the actual ultrasound you will see the tumor in the center of the circular bladder.

Composition

There are many different types of bladder stones. Some of the most common ones include:

Struvite

This urolith is diagnosed in almost half the cases of bladder stones. It is also called MAP (Magnesium-ammonium-Phosphate), or triple phosphate. It is the predominant stone type in female dogs of all breeds except Dalmatians.

Several factors predispose dogs to getting struvite uroliths:

• Excess struvite crystals in the urine that set the stage for the formation of the urolith. Some breeds, notably Miniature Schnauzers, have a genetic predisposition to forming excess amounts of these crystals in the urine.

• Urinary Tract Infection (UTI)- some bacteria produce a byproduct called urease. Urease will increase the pH of the urine and promote ammonium in the urine.

• The formation of an alkaline (pH greater that 7.0) urine from the diet or urease producing bacteria will cause the struvite crystals to precipitate out of solution and begin the formation of a urolith.

• Urine that stays in the bladder longer than usual gives the struvite crystals further opportunity to precipitate out of solution and form a urolith.

  Struvite uroliths come in many different shapes and sizes, are radiodense, and form in an alkaline urine. Miniature Schnauzers are the most commonly affected breed.

Calcium Oxalate

This is the second most prevalent type of urolith after struvite, making up around 30-50% of the uroliths we diagnose, especially in male dogs of all species except Dalmatians. They come in two versions; the monohydrate and the dihydrate. Sometimes the two are found together, sometimes they are found with other uroliths like calcium phosphate, Strive, or ammonia urate.

Feline

These tend to occur in neutered middle aged cats, especially Burmese, Himalayan, and Persian breeds. One of the predisposing conditions might be an increased calcium level in the bloodstream. These uroliths tend to form in an acidic urine.

Canine

This is a problem most commonly in older male dogs. It is suspected that there is a correlation with hormone changes that occur as a pet ages. Several breeds are prone:

• Schnauzer
• Lhasa apso
• Yorkshire terrier
• Bichon Frise
• Shih Tzu
• Miniature poodle

Several predisposing factors work together to increase the chance of this urolith forming:

Urate and ammonium Urate

This is a common urolith found in Dalmatians around middle age, with males affected much more often than females. This is because they metabolize protein differently in the liver, with the end result being uric acid buildup in the urine. In addition to their high prevalence in Dalmatians, they are found in Bulldogs and Yorkshire terriers.

There does not seem to be a connection with a urinary tract infection, and they tend to form in an acidic urine.

Urate stones are radiolucent. If they get large or covered with other minerals they might become radiopaque. Urate calculi tend to be small and occur as several stones. These stones usually form in the bladder, and when passed through the urethra, can become lodged.

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Ammonium urate uroliths are sometimes formed in pets with PSS (liver disease) due to improper metabolism of ammonia to urea. This will cause excess uric acid levels in the bloodstream. The kidneys filter out this excess uric acid in the production of urine, thus increasing the level of uric acid in the bladder. The excess ammonia that is in the bloodstream from the liver problem also builds up in the urine in the bladder. These two compounds combine to form the ammonium urate bladder stone.

Dogs with ammonium urate bladder stones might have ammonium urate crystals in their urine and a low specific gravity (dilute urine). These stones might not be seen on a radiograph because they are radiolucent. This same radiograph might also show a small liver, an indication of PSS. This small liver is due to the diverted blood flow to the liver. Dogs with PSS will commonly have abnormalities in the blood sample to give us further clues.

Compound Uroliths

Most bladder stones are caused predominantly by one type of mineral. The more common ones have been described above. In a small percent of cases, the bladder stone is caused by a combination of minerals in similar quantities. These stones are called mixed uroliths. Some bladder stones consist of a core mineral surrounded by a lesser amount of a different mineral in a different layer. These are called compound uroliths. Why some minerals form mixed uroliths and others form compound uroliths is not understood.

Compound uroliths form when the factors that predispose to one type of stone formation have now changed to factors that favor a different type of stone formation. If a struvite stone is treated with antibiotics and urinary acidifiers the problem tends to resolve. The change in urine pH might promote excess calcium in the urine, resulting in a shell of calcium oxalate formation around the core struvite stone. The opposite can occur also- a struvite stone can form over a calcium oxalate stone.

In general, these stones are removed surgically and an effort is made to medically prevent the mineral that is at the core of the stone.

Miscellaneous Uroliths

There are other uroliths that occur, although they are relatively uncommon. They include cystine, silica, calcium phosphate, and miscellaneous minerals.

Medical Treatment

Struvite

Struvite bladder stones can literally be treated medically with a food called Hills S/D. The mechanism involves creating a urine that is undersaturated with the crystals that caused the struvite urolith to form in the first place. This undersaturation literally cause the urolith to dissolve in the urine, and then get urinated out.

S/D has several modifications in its ingredients to set up this undersaturated urine. Its reduced in protein, so there is less ammonia buildup in the bladder from bacteria. Magnesium and phosphorous are restricted also. With less contents of the minerals that form the struvite urolith (magnesium, ammonia, and phosphorous- MAP) the urolith starts dissolving.

S/D also has an increased amount of salt (sodium chloride). This promotes drinking and urination and literally helps flush the struvite crystals out of the bladder. It also changes the pH to a more acidic state, which further makes the struvite stone dissolve.

S/D must be the only food fed for it to work. We can monitor whether or not an owner is doing this by looking at the pH of the urine along with the specific gravity of the urine. also, the BUN (blood urea nitrogen) of a pet on S/D should be lower than normal.

We have clues from other diagnostic tests to help decide if a urolith found in the urinary bladder on a radiograph is truly struvite. The urinalysis gives us an idea of the composition of the urolith by looking at the crystals in the sediment. The pH of the urine will be alkaline. Also, the presence of bacteria on a culture in a breed that is prone to struvite uroliths is also a strong indication.

If bacteria are found on a urine culture (rare in cats) then antibiotics must be used simultaneously while a pet is on S/D. It must be the correct antibiotic, so the importance of the urine culture is obvious. Both S/D and antibiotics are used for one month after the stone is no longer visible on a radiograph. If the urolith is still present after 2 months of S/D and antibiotics, then surgery should be performed. Most pets need to be fed S/D for 4-6 months for complete resolution.

S/D is restricted in protein, so it is not a complete diet for long term use in dogs. While on S/D your pet's blood should be monitored to ensure there are no side effects of the restricted protein. Feline S/D is not protein restricted, so it can be used for the rest of your cat's life.

Calcium Oxalate

The only treatment for these uroliths is surgical removal.

Urate

If there is no PSS these uroliths can sometimes be handled medically also. A food called Hills U/D should be used. It is low in purines and has restricted protein. a medication called allopurinol is given which helps minimize the amount of uric acid produced in the urine. Potassium citrate is also used to make the urine less acidic, although this might occur with the use of U/D alone. Adding salt to the diet or mixing water with the food will also promote urination of the urate crystals. Recurrence is common, so this diet needs to be used for the life of your pet, especially in Dalmatians. We will talk more about this later in the prevention section.

Surgical Treatment

The surgical removal of a stone in the urinary bladder is called a cystotomy. It involves making an incision into the abdomen, exteriorizing the urinary bladder, removing the stone(s), and resuturing the bladder. The following surgeries demonstrate the removal of two different types of bladder stones.

This next section contains graphic pictures of actual surgical procedures performed at the hospital. If you don't want to see them, click here to pass up these pictures and learn about prevention.

An incision is made into the pets abdomen and the bladder is brought out through the opening. After the bladder is exteriorized two" stay sutures" are placed. The stay sutures hold the bladder in place outside the abdomen while the surgery proceeds. They are much gentler than holding the bladder with instruments that might damage this delicate tissue. This bladder is particularly thick, due to the large size of the stone and the chronic nature of the problem. This urolith is the one you saw in the radiograph previously.

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The lining of the urinary bladder is examined, and cultures and biopsies are taken if necessary. It is also carefully examined for other stones that might not have shown up on the radiograph.

The bladder is gently flushed if necessary, and a urinary catheter is sometimes placed. This catheter will prevent the bladder from over distending and rupturing in the first day postoperatively.

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Some dogs have multiple small stones as opposed to one large one. How many stones do you see in this urinary bladder?

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The small size of these stones allow a much smaller bladder incision. The time it takes to suture this bladder is significantly less than the large stone above, and it will heal faster. There is a tradeoff though- much more time is spent in removing these numerous small stones.

Stones this small tend to locate at the junction of the bladder and urethra. Not all of them can be removed by reaching in with a hemostat and removing them. a urinary catheter needs to be placed and the stones are flushed up so they can be grabbed with the hemostat.

Here are the culprits-did you find all 17 on the x-ray?

Seven sutures were put in this urinary bladder to seal it. They will slowly dissolve over the course of several months. At this point in the surgery we will place the bladder back into the abdomen, suture the abdominal muscles back together, and give pain medication.

The bladder is not the only location for stones to occur. This dog has 2 in its urethra at the tips of the black arrows.

A close-up view give better visualization. This is an example of stones that are lodged at the ischial arch, described previously in the symptoms section.

We passed a urinary catheter under anesthesia and started flushing the stones towards the bladder. Once they are in the bladder they can be removed via cystotomy. In this view you can see how the stones have moved slightly from the flushing. It took 8 more flushings to move them all the way into the bladder.

This is a picture of the bladder during the actual flushing. The bladder has an incision in it because this dog also had a calculi in its bladder, which has already been removed. It takes significant force to move the stones from the urethra back into the bladder. You can see the saline solution flowing out of the bladder towards the left (arrow).

These are the three stones that were removed- one was in the bladder and two were in the urethra.

This is the stone analysis of the above uroliths verifying that they are calcium oxalate stones.

The center of the stone was cultured. The culture yielded an organism called nonhemolytic coagulase negative Staph. This bacteria is sensitive (S) to 5 of the antibiotics on the list.

There is another common area for stones to lodge in the urethra of male dogs. Towards the end of the urethra male dogs have a boney structure that surrounds the urethra. This structure is called the os penis. In this area the urethra cannot expand to let a stone pass, hence stones commonly lodge here.

The white line outlines the urethra as it passes from the bladder, goes over the ischial arch and through the os penis. The arrow points to the beginning of the os penis, the area where a stone would lodge.

There are several sequelae to these stones in the urethra. If the urinary bladder has been distended long enough the urinary bladder loses its ability to contract and urinate properly. Nerve damage in the spinal cord can also cause this. The end result is an animal where the urine builds up in the bladder until the point it passively overflows. These animals are predisposed to chronic infections, not to mention the pain and discomfort of a distended urinary bladder.

This radiograph shows a dog with a seriously distended urinary bladder (UB). Its the large white area in the middle of the radiograph. The dark area to the left and slightly overlapping the front of the urinary bladder is the stomach (S) filled with food.

We use the laser in some surgeries because it dramatically minimizes bleeding. The following movie shows a laser incision in a bladder, removal of many large calculi, removal of small calculi, flushing the bladder to remove all of the small calculi, and the initial suturing of the bladder. Double click on it to play.

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