Stones in the urinary tract are common in dogs and cats. Even though dogs and cats do get kidney stones, it is bladder stones that causes more problems. The medical terms for bladder stones are urolithiasis or cystic calculi. We will use stone, calculi, and urolith synonymously in this page.
Stones can also occur in the kidneys, where they are called nephroliths. This page will limit its discussion to stones in the bladder.
We added a short QuickTime video to the ultrasound section of this page. Towards the end of the page we have another video on a surgery where we remove bladder stones with the laser. Make sure you have QuickTime from apple on your machine.
There are several factor, usually working in combination, that lead to urolith formation:
Urine that is saturated with excess amount of certain minerals is prone to form bladder stones. These minerals commonly include magnesium, phosphorous, calcium, and ammonia. Most stones consist of an organic matrix of protein surrounded by crystalline minerals.
Diet can have a major impact here, and is one of the primary methods we use to treat and prevent uroliths.
pH is an indicator of acidity by measuring the hydrogen ion concentration. A pH of 7 is neutral. Below 7 is acidic, above 7 is alkaline. As a general rule, dog and cats tend to have an acidic urine normally. Some uroliths have a propensity to form in acidic urine while others tend to form in alkaline urine. Urine pH needs to be measure immediately upon voiding from the bladder for it to be accurate.
Some uroliths form due to the presence of bacteria in the urine, so control of these bacteria is important. Bacteria are diagnosed by culturing the urine or the inside of a stone after surgical removal. Normal urine is sterile, so any bacteria cultured from the urine is abnormal. When bacteria are cultured a pet has a urinary tract infection (UTI) and needs antibiotics. Common bacteria in UTI’s include E. coli, Staph. spp., and Proteus.
If any bacteria are cultured in the urine our laboratory will test numerous antibiotics to determine which are the best ones to eliminate the bacteria. This is called sensitivity testing.
Liver shunts are an abnormality of blood flow to the liver. Blood that would normally flow through the liver now bypasses the liver. One of the many consequences of this disease, called Portosystemic shunts (PSS), is the formation of ammonium urate bladder stones.
Medications can predispose pets to forming bladder stones. Sometimes they do this by increasing the calcium level in the urine. Medications that increase or decrease the pH of the urine can also set the stage for stone formation. Some medications can actually cause formation of stones when used for long periods of time. The following list includes some of these medications:
Predisposing causes of bladder stones include pets that are not drinking enough or are not allowed to urinate frequently. Bacteria and stone forming chemicals stagnate in the urinary bladder and increase the chance of a stone forming. Mechanical flushing of the bladder, in the form of normal and frequent urination, will prevent this. Always make sure your pet has access to fresh water, changed several times per day, and the ability to urinate frequently. As a matter of fact, if you feed dry food you should be giving more than one cup of water per cup of dry food. An easy way to get around this important requirement for water is not to feed dry food at all. Your pet’s urine should be clear, with no odor or color, and your pet should urinate every few hours. Sometimes these common sense suggestions are so obvious that we tend to forget about their importance.
Typical symptoms include:
- Straining to urinate (stranguria)
- Blood in the urine (hematuria)
- Urinating small amounts frequently (pollakiuria)
There might also be excess urination (polyuria), pain in the rear quarters, reluctance to jump or play, or even lethargy and a poor appetite. Some pets can have bladder stones without any apparent symptoms at all!
The bladder stones can pass out of the bladder and lodge in the urethra, especially in male dogs due to the smaller diameter of their urethra. In some cases they can block the flow of urine, which is a medical emergency. This will cause problems with the kidneys, leading to the buildup of toxic waste products. Common areas for these urethral obstructions are the ischial arch near the pelvis and further down the urethra at the os penis. Both of these areas have small diameter urethras that do not expand to allow passage of a stone. You will learn more about this later.
A urinalysis is crucial in making a correct diagnosis. The pH of the urine, and the presence of bacteria or crystals all provide valuable information.
Abnormalities that can be found in the urine in a pet with a urolith include:
- Increased white blood cells
- Increased protein
- Low or high pH
The presence of crystals (crystalluria) is a sign that a urolith is possible, and usually warrants further investigation.
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.
Bacteria are implicated in many cases of urolithiasis.htm. Culturing the urine will let us know what bacteria, if any, are involved, and which antibiotic(s) will be effective. In addition to serving as a nidus for urolithiasis, these bacteria can ascend from the bladder into the kidneys, causing a pyelonephritis.
This is a culture & sensitivity report we received from our lab. We sent them a sample of urine and asked them to let us know if there are bacteria in the normally sterile urine. The organism they cultured is E. coli, a common bacteria in both animals and humanoids. This bacteria is pathogenic in the bladder, and is causing a urinary tract infection. The lab tests numerous antibiotics and determines which antibiotic(s) E. coli is sensitive to. As you can see from this culture, E. coli is resistant (R) to numerous antibiotics.
After we have determined that bacteria are part of the problem our lab provides us with information on how effective antibiotics will be at the level of the bladder.
One of the best methods to make a diagnosis of uroliths is radiography. Many stones are radiopaque, which means they show up vividly on an x-ray. Radiopaque stones include struvite and calcium oxalate. Some stones are radioulucent, and depending on size and number, do not show up on a regular x-ray. These stones are diagnosed by injecting air, dye, or a combination of both, into the bladder to outline any suspected stone. Ultrasound is a great way to detect these stones. Radiolucent stones include ammonium urate.
This is the side view of a dog with a very large radiopaque stone in its urinary bladder
This is a picture of the stone that was in the x-ray above
Other stones aren’t always this smooth. Even though this stone is small, the roughened edges were probably painful in this dogs bladder.
This dog has stones in the bladder and in the urethra as marked by the two arrows on the right. The arrow on the left is showing an enlarged liver lobe.
Click on the photo to enlarge it.
Did you notice the stones in the kidney also?
Radiographic appearance right after surgery to remove the stones in the urinary bladder
Ultrasound is a very precise method to diagnose stones in the urinary bladder. It is particularly helpful for radiolucent stones and anatomical defects of the bladder wall. In this picture U BLAD is the urinary bladder filled with urine (the dark area), and CALC are bladder stones (calculi).
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. 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.
There are many different types of bladder stones. Some of the most common ones include:
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.
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, struvite, or ammonia urate.
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.
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:
Several predisposing factors work together to increase the chance of this urolith forming:
- Increased calcium in the bloodstream (hypercalcemia)
- Increased calcium in the urine (hypercalciuria) with no hypercalcemia
- Concurrent Cushing’s disease
- Use of cortisone
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.
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.
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.
There are other uroliths that occur, although they are relatively uncommon. They include cystine, silica, calcium phosphate, and miscellaneous minerals.
Struvite bladder stones can be 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.
The only treatment for these uroliths is surgical removal.
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.
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.
An incision is made in the bladder just big enough to gently squeeze this large stone through. We want to make this incision as small as possible to minimize anesthetic time, decrease discomfort postoperatively, and prevent a healing bladder from rupturing when it gets distended with urine.
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.
It is critical that the bladder is sutured back together properly. This is especially important with an incision this large and with a bladder that has had a large stone irritating it for a long period of time. The sutures need to be placed strong enough to hold the bladder together, yet gentle enough to allow the irritated bladder to heal.
Some dogs have multiple small stones as opposed to one large one. How many stones do you see in this urinary bladder?
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 it 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 and they dribble. 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.
Medical dissolution or surgical removal of the bladder stone is the first step in the process. The next, and just as important step, is the prevention of the stone’s recurrence. Some of these stones will require a diet change only, while others might require long term medication. Some breeds are predisposed to forming stones in spite of what we do to prevent them. Our doctors will set up a specific protocol for your pet based on the breed and type of stone removed.
Long term follow up is important. Your pet will have to return periodically to recheck a urinalysis, culture the urine for bacteria, and x-ray the bladder. Many stones recur because owners forget the importance of long term prevention.
At all times make sure your pet has access to fresh water and the ability to go to the bathroom. This treatment alone will go a long way to prevent recurrence. Giving your pet food that has more moisture will increase the flow of water through the urinary system and minimize crystal formation in the bladder. As a general rule, we do not recommend adding salt (sodium chloride) to the food to get your pet to drink more water because it might promote calcium formation in the urine, thus setting the stage for a stone to form. Your doctor will let you know if this applies in your case.
Pets that have struvite urolithiasis, whether treated surgically or medically, have a chance of recurrence if not monitored carefully. If the urine is alkaline on a urinalysis it should be cultured to check for bacteria. Antibiotics are indicated if the culture is positive. If the pH stays alkaline in spite of antibiotic therapy, then Hills C/D should be used. It will help maintain an acidic urine, and has some mild restrictions in protein and minerals. As a general rule, we recommend C/D for all pets that have had struvite crystals. It can be used on a long term basis, and is helpful in preventing FLUTD in cats. S/D can also be used long term in cats.
Recurrence rates with this urolith are high, so a long term plan and commitment to sticking with it are important.
Baseline data consisting or radiographs, urinalysis, urine culture, and blood panel needs to be obtained. Particular attention is paid to the blood calcium level.
A diet with reduced quantities of protein, calcium, and sodium, that also does not make an acidic urine, is the ideal diet to feed. Too much of a reduction in these nutrients can be detrimental, so no supplements should be added. The primary diet in the cat that accomplishes this ideal is Hills Prescription Diet K/D. In dogs, K/D, W/D, and U/D are used. The use of U/D might preclude the use of potassium citrate as long as there are not calcium oxalate crystals in the urine and the pH is alkaline. There is a C/D that treats calcium oxalate uroliths in cats.
Certain foods that are high in oxalates or calcium, or foods that increase calcium levels, must be avoided. They include high protein foods, spinach, rhubarb, parsley, milk products, and table salt.
When we diagnose a calcium oxalate stone we will check the calcium level in the bloodstream to make sure it is not abnormally high. This normal calcium level was from the dog above that had the surgery to remove the calcium oxalate stones from its bladder and urethra.
Vitamin C and D, along with drugs that make the urine more acidic, should not be added to the diet. Cortisone also should be used cautiously because it increases the calcium level in the urine.
Potassium citrate will inhibit calcium oxalate crystal formation and keep the pH of the urine in the ideal range. We will use this if U/D does not keep the urine alkaline.
After surgery your pet should return in 2 weeks for a urinalysis. If there are calcium oxalate crystals in the urine we will add potassium citrate as per above. If there are no crystals we will not need to do a recheck for 3 months. At this 3 month recheck of the urine we will also re-radiograph the bladder and check a blood panel noting the calcium level.
Two weeks after surgery this is the urine sample of the dog with the above stones. This is what we want to see- no crystals, no bacteria, and an alkaline pH.
If calcium oxalate crystals persist in the urine 2 weeks after adding potassium citrate, we will add Vitamin B6 to the diet. If the B6 does not eliminate the crystals, we will use a drug called hydrochlorothiazide. Use of this drug requires close monitoring of the potassium level and the calcium level in the bloodstream.
A urinalysis should be performed every 3-6 months to look for crystals in the urine and monitor the pH. A urine culture should also be performed at this time to decide if antibiotics are needed.
Ammonium Urate and Urate
Medical care for Dalmatians after surgery includes:
1. Increasing water consumption so the specific gravity of the urine is near 1.018. adding water to dry food, feeding more canned food, and adding encapsulated light salt (KCl) all will help.
2. Feeding a diet low in purines. Diets low in purines include the Hills Prescription Diets K/D or U/D dry and U/D canned.
3. Increasing the pH of the urine to 7.0-7.5. The above diets might accomplish this pH. If not, adding oral potassium citrate to the diet will help.
4. Controlling urinary tract infections, if any, by performing urine culture and sensitivity tests every 3-6 months, and using antibiotics on a long term basis if needed.
5. Adding allopurinol to the diet to prevent the conversion of purine to uric acid.
This therapy needs to be followed diligently for the life of your Dalmatian.
Medical care for cats and non-Dalmatian dogs after surgery is similar. Most of these uroliths are caused by a PSS, thus surgery to correct the liver problem will help prevent the recurrence of these stones in the bladder. In some PSS’s the liver problem cannot be completely resolved, adding to the risk of formation of these bladder stones in the future. Long term therapy is similar to Dalmatians:
1. Increasing water consumption so the specific gravity of the urine is near 1.018 for dogs and 1.025 for cats. adding water to dry food, feeding more canned food, and adding encapsulated light salt (KCl) all will help.
2. Feeding a diet low in purines for dogs. Diets low in purines include the Hills Prescription Diets K/D or U/D dry and U/D canned. For cats feed diets that do not acidify the urine, which unfortunately, many do to prevent FLUTD.
3. Increasing the pH of the urine to 7.0-7.5. The above diets might accomplish this pH. If not, adding oral potassium citrate to the diet will help.
4. Controlling urinary tract infections by performing urine culture and sensitivity tests every 3-6 months, and using antibiotics on a long term basis if needed.
Since these stones have a combination of minerals they present a dilemma in their prevention. In general, it is recommended that an effort is made to prevent the mineral that forms the core of the stone.
The majority of compound stones are struvite core with a calcium phosphate outer core.
An additonal treatment modality, used especially after we remove the urolithiasis is VNA. It is a non-invasive and non-painful way to stimulate the nervous system to increase blood flow to the kidneys. This will increase urine output, making it more difficult for the stone to start all over again. It is a highly effective way to help prevent the problem from recurring.
Pet food manufacturers have dramatically increased their sophistication in treating bladder problems in dogs and cats. It is because of these advances that we are able to treat and prevent many of these uroliths medically. Unfortunately, a change in food to treat struvite uroliths predisposes a pet to calcium oxalate uroliths, and vice versa. One of the ways we have gotten around this is to produce a food in cats, called c/d multicare, that prevents both.
In order to remedy this situation it is important to make a correct diagnosis so that the proper type of food can be used. To ensure that you are not setting up an environment for a different urolith to form in the future, the urine should be monitored every 3 months.
Another remedy is to use combined diets that have been formulated to take care of both of these calculi simultaneously. This might help if compound uroliths are present.