Stones in the urinary tract (kidneys, ureters, and urinary bladder) are common in dogs and cats. Even though dogs get kidney stones, it is bladder stones that cause more problems. The medical terms for bladder stones are urolithiasis or cystic calculi. We will use stone, calculi,and urolith synonymously in this page. The two most common calculi are calcium oxalate and struvite.




Stones can also occur in the kidneys, where they are called nephroliths. This page will limit its discussion to stones in the bladder.

Towards the end of the page we have a video of a surgery where we remove bladder stones with the laser.

There is a lot to digest in this page, so pace yourself. This is because bladder stones are complicated. You will be learning about crystals, pH, liver shunts, sodium, potassium, calcium levels, etc, etc,.  If you get bogged down don’t give up, take a break, and come back to it.

On rare occasion a dog can have a bladder stone lodge in the urethra and it cannot urinate. This is a medical emergency requiring immediate veterinary care. The Long Beach Animal Hospital, staffed with emergency vets, is available until the evenings 7 days per week to help if your pet is having any problems, especially shock, pain, breathing hard, or bleeding.

Think of us as your Long Beach Animal Emergency Center to help when you need us for everything from minor problems to major a major emergency. We serve all of Los Angeles and Orange county with our Animal Emergency Center Long Beach, and are easily accessible to most everyone in southern California via Pacific Coast Hwy or the 405 freeway.

If you have an emergency that can be taken care of by us at the Animal Emergency Hospital Long Beach always call us first (562-434-9966) before coming.  This way our veterinarians can advise you on what to do at home and so that our staff and doctor can prepare for your arrival. To learn more please read our Emergency Services page.

Graphic pictures and videos on this page.

Cause

There are several factor, usually working in combination, that lead to urolith formation:

Mineral Crystals

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.

Urine pH

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, dogs tend to have an acidic urine. 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.

Bacteria

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 during a sterile urinalysis, or by culturing 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. We also do a test called MIC (Minimum Inhibitory Concentration) to let us know the best antibiotic to use and the best dose of that antibiotic.

Diseases

Liver shunts (Porto-Systemic Shunt- PSS) 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 is the formation of ammonium urate bladder stones.

Urine showing ammonium urates

This was our first clue this pet had a liver shunt

Ameroid ring for liver shunt surgery

In case you are curious, this is called an ameroid ring. It is used to repair the shunt, and you can see how it was used during surgery of the liver shunt repair.

Medications

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:

  • Lasix
  • Cortisone
  • Ascorbic Acid (Vitamin C)
  • Sulfa medications
  • Tetracycline’s

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 of bladder stones:

Straining to urinate (stranguria)

Blood in the urine (hematuria)

Urinating small amounts frequently (pollakiuria)

Often times there are no symptoms at all, and the problem is discovered on routine abdominal palpation or radiography.

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 can 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.

Diagnostic Tests

Urinalysis

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:

  • Blood
  • Increased white blood cells
  • Increased protein
  • Crystals
  • Bacteria
  • Low or high pH

The presence of crystals (crystalluria) is a sign that a urolith is possible, and usually warrants further investigation. At this point we might take radiographs, do an ultrasound, do a urine culture, or recheck it in the next few weeks or months.

Urinalysis Report

This is an example of a cat urinalysis. The pH is high (alkaline), there is excess protein, and there are struvite and ammonium rate crystals

Urine Culture

Bacteria are implicated in many cases of urolithiasis. 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 directly from the bladder, 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 by using an MIC (minimum inhibitory concentration).

 

Urine Culture and Sensitivity

This urine culture of an E. Coli bacteria says that the 2 antibiotics in red will the best ones to use

Radiography

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 radiolucent, 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.

Bladder stone in xray

Any problem finding the large bladder stone in this radiograph?

Xray of bladder stones

Did you find both of them?

Large bladder stone

This is what a stone like the large one above would look like when removed

X-ray of bladder stone

Not every stone is so smooth

Rough edges of removed stone

Think of what this would feel like in your bladder

Many dogs are seriously inbred, and when we find one problem like bladder stones oftentimes there are others. This is the full abdominal radiograph of the dog with the rough stone. It has two other problems that are circled in red.

Xray of arthritis and liver

The top circle shows arthritis along the spine. The bottom circle shows an enlarged and rounded liver

Bladder stones also occur in CDT’s (California Desert Tortoises) and Iguanas. These animals are vastly different anatomically and physiologically when it comes to bladder stones, and once they are removed surgically their prevention is different compared to dogs.

Tortoise radiograph with large bladder stone

CDT’s don’t fool around when they get bladder stones, and when they get them, they get them big

X-Ray of Iguana bladder stone

They are not quite that big in Iggies

Ultrasound

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.

Ultrasound of bladder stones

This ultrasound bladder stone diagnosis was in 1993. Compare it to the quality of the ones below from the last few years.

Ultrasound of small bladder stone

This small and radiolucent bladder stone (the two yellow + marks) were picked up by ultrasound

Ultrasound of large bladder stone

This one is easier to see

When we perform an ultrasound of the abdomen and urinary bladder we are not just looking for radiolucent bladder stones. We are looking for any pathology. The following ultrasound is from a pet that had symptoms of straining to urinate and blood in the urine, classic signs of a bladder stone. It turned out to be a cancer called TCC (Transitional Cell Carcinoma)

Ultrasound of bladder cancer

It is large and fill half of the lumen of the urinary bladder

Cancerous bladder during surgery

The red arrow points to a bulge on the outside of this bladder taken during surgery. This bulge is part of the cancer. 

Composition

We send our stones to the Minnesota Urolith Center at the Univ of Minnesota. They have more experience than any other place in the world regarding animal bladder stones.

Urolith center form

Bladder stones are complicated, and made of many layers and compounds

Stone composition

They give us a detailed report on the stone

Stone prevention protocol

This is the protocol for a calcium oxalate stone to prevent recurrence

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. Struvite uroliths come in many different shapes and sizes, are radiodense, and form in an alkaline urine.

It is the predominant stone type in female dogs of all breeds except Dalmatians. This is because of the high association of struvite crystals with urinary tract infections, which are more common in female dogs. If a female dog gets a bladder stone, 80% of the time it is struvite because of this association.

Dogs under a year of age, no matter what  sex, get struvite as the most common bladder stone for this same reason. Miniature Schnauzers are the most commonly affected breed, along with bichon frise, cocker spaniels, and miniature poodles.

Canine  urine is commonly supersaturated with struvite crystals due to the high protein and mineral content of current diets. This excess of these crystals in the urine, stored in the urinary bladder, combines with bacteria to set the stage from the formation of bladder stones (uroliths).

Bacteria that are commonly implicated include Staphlycoccus, Enterococcus, and Mycoplasma.  These bacteria increase the amount of organic debris available for crystallization.

These bacteria also produce urease as a by-product of their metabolism. They  split the urea in urine into ammonia and carbon dioxide. As this ammonia is broken down it changes the pH of the urine from its usual acid (pH less than 7) to alkaline (PH > than 7).

High urine ammonia concentrations in the urinary bladder can damage the glycosaminoglycans that help prevent the bacteria from adhering to the bladder mucosa (interior lining of the bladder). When we treat for this disease we address these issues.

What does all of this mean?

Excess struvite crystals in the urine  set the stage for the formation of the urolith.

  • 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 from 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.

This is especially true when the urine pH is highly alkaline, which can occur with the use of some drugs, in certain diets, and when the tubules of the kidney are diseases. If there is a bacteria involved it is usually Staphlycoccus.Staph bacterial culture

An example of a culture report show a Staph infection in the urine

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, struvite, or ammonia irate.

They show up well on a radiograph. They form in an acidic or neutral urine (pH is 7 or just slightly less). Recurrence is common, so diligence on your part is needed to prevent recurrence.

Feeding an older pet with Kidney problems a food like Hills Prescription Diet K/D may slow or prevent further growth.

If this stone is small and not causing any apparent problem it can be monitored. Some pets will have high calcium (hypercalcemia) in the bloodstream.

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 for skin allergies or Addison’s (hypoadrenocorticism) disease.

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:

Miniature Schnauzer

Lhasa apso

Yorkshire terrier

Bichon Frise

Shih Tzu

Miniature poodle

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.

Pile of urate stones

When we encounter this stone usually there are many of them

Pile of bladder stones

If you think the above picture is a lot of stones take a gander at this pile, and this is not even all of them!

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 (you saw this in a urinalysis earlier in this page) 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.

Treatment- Medical

Struvite

Most cases of struvite are treated surgically. The procedure is explained below.

Struvite bladder stones can also 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 causes the urolith to dissolve in the urine, and then get urinated out. It is a slow and gradual process, although most pets get relief from straining and blood in the urine soon after starting this diet.

S/D has several modifications in its ingredients to set up this undersaturated urine. It’s 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.

The rate of dissolution is proportional to the surface area of the stone exposed to this now undersaturated urine and the control of the urinary tract infection in dogs.  Feline struvite stones tend to dissolve faster than canine because bacteria are not implicated.

Measuring bladder stone

We can measure the size of a stone with our digital x-ray to make sure it is getting smaller early in the process of dissolving it

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 in dogs 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 there is a persistent urinary tract infection we might use a urease inhibitor called acetohydroxamic acid. Urinary acidifiers are usually not used.

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. It should be fed for an addition 30 days after there is no longer any stone based on a radiograph.

S/D is restricted in protein, so it is not a complete diet for long term use in dogs. It also should not be used pregnant dogs, lactating dogs, hound dogs, and after surgery, due to this protein restriction. While on S/D your dog’s blood should be monitored to ensure there are no side effects of the restricted protein.

Due to the high salt (sodium chloride) it should not be used in dogs with congestive heart failure and hypertension.

Calcium Oxalate

The only treatment for these uroliths is surgical removal. This is the easy part, it’s preventing their recurrence that is difficult. The protocol in how to do this was shown earlier.

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.

Treatment- Surgical

Pre-Surgical Preparation

Preparing for the surgery is just as important, and in some surgeries more important, than the actual surgery. We do a wide variety of bladder stone removals on a wide variety of species. At the beginning of this page there were links to how we do a cystotomy on tortoises and iguana’s.

Rabbit being examined

All of our surgical patients get a pre-anesthetic exam within 24 hours of surgery, even bunnies

Examining a bearded dragon

That includes reptiles also

After the exam there are routine pre-anesthetic tests we perform. The two most important ones are a blood panel and a pre-anesthetic EKG.

The blood panel is performed several days prior to surgery so that it is returned and assessed in time. It includes a CBC, Chem panel, and a urinalysis. Below is just a part of the chem panel.

Rabbit normal blood glucose

This is one part of a pre-anesthetic blood panel. The glucose is circled to let you know that this high number could be normal, it all depends on the species (this is a rabbit blood). In a human this would be a high blood glucose indicative of diabetes mellitus (sugar diabetes).

The pre-anesthetic EKG or ECG (electrocardiogram) only takes a few hours, and is usually performed the morning of surgery so that we have the most current data. This differs from a sick pet that is getting an EKG. This is performed by our cardiologist Dr. Fred Brewer when he is available to come in.

Teaching EKG

This is a teaching EKG to show our students abnormalities to look for. If you like this kind of stuff our Heart Page is the place for you. 

Cardiologist using a stethoscope

This is Dr. Brewer and one of our student externs listening to the heart of an ill cat

Cardiologist Teaching Student

On occasion, especially on a dog or cat that is elderly, or has a significant heart murmur or heart disease, Dr. Brewer will perform an echocardiogram prior to surgery so that we can safely anesthetize this higher risk patient

Anesthesia

Once we have analyzed our pre-anesthetic exam and tests we will proceed to anesthetize our patient. They are given pre-anesthetic tranquilizers and pain medication to calm them down. Our Anesthesia Page has much more information on this.

Anesthesia monitor

We use a sophisticated monitor to keep track of important physiologic parameters during surgery

Nurse anesthetist with stethoscope

Even with all of that high tech monitoring equipment we still stay hands-on during the whole procedure

Surgeon washing hands

Once our surgeon has scrubbed up and is  in sterile gown, gloves, and mask, the surgery begins

Surgeon preparing sterile instruments

While our staff is preparing our patient our surgeon is getting instruments ready. Only once he is satisfied that everything is in order does the surgery begin.

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 re-suturing the bladder.

We usually use the laser to make an incision in the bladder. Here is a link to how we do surgery at our hospital.

Many of these bladders are thickened from chronic irritation, which means they have an extensive blood supply. You will see that in the following photos. When you watch the laser surgery on one of these thickened bladders notice the blood supply and how little bleeding there is. This is a major advantage of using the laser.

The laser is a precise machine customized for each surgery. Watch how we set it up and how it checks its circuits and calibrates itself in this video

When we make the incision into the bladder the laser is used in almost all cases because of dramatically less bleeding during the surgery and dramatically less inflammation after we remove the stone and suture the bladder.  For those of us that have had surgery we know the importance of minimizing post operative pain. Your pet will be happy we used the laser!

Laser-cystotomy

This is a close up of the laser making the incision into the urinary bladder in order to remove the stone. Look at the blood supply on the outside of the bladder, without any bleeding at the incision site.

A video of the same bladder

 

How we suture the bladder after the stones are removed

The urinary bladder is not the only location for stones to occur. In addition to the kidneys (more common in people than bladder stones) and ureters, the urethra has it goes over the pelvis (especially in males) can harbor a bladder stone (or two)!

This occurs when a stone decides to leave the urinary bladder and find its way out. When it in encounters the narrow urethra it becomes lodged, and you literally will not be able to urinate. This causes post-renal uremia, with subsequent backup of urine to the kidneys, causing serious disease and even kidney failure.

Do you see the two stones in the pelvic urethra of this dog? 

Arrows pointing to stones

The arrow on this close up point to the two stones

A catheter was advanced to the two stones, and they were flush back to the left into the bladder. It took eight flushings to move them.

Arrows pointing to stones

This is after the first flushing. Compare the stone on the left to the X-ray above and you can see that it has moved to the left.

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. This can prevent urination, with potentially serious consequences for the kidneys.

Catheter in the pelvic urethra

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.

Arrow pointing to stone
The arrow points to a stone at the os penis

Pointing to moved stone

It was flushed back into the bladder with a catheter. Here it is part way back.

Stones in bladder

After a few more flushings it was pushed back into the urinary bladder, along with the other stones that are already in the bladder. It was removed doing a routine cystotomy.

Bladder empty of stones

After the large stones we removed the smaller ones, which are hard to visualize in the bladder, are flushed out. This radiograph after surgery shows there are no more stones in the bladder.

Appearance of rough stone

This is the stone that was originally stuck behind the os penis, and flushed back into the bladder. It is only a few millimeters in size, but with its rough appearance, is probably not very comfortable to say the least.

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.

The other problem is damage to the kidneys. When a pet cannot urinate due a blockage like this it causes what is called post-renal uremia. In essence, the kidneys have shut down and waste products are building up in the bloodstream. You can learn more about the damage these waste products cause from our Kidney Page.

Distended urinary bladder

This radiograph shows a dog with a seriously distended urinary bladder (UB). It’s the large white area towards the right in the middle of the radiograph. It is pushing the intestines to the left. This bladder is in danger of rupturing. 

Prevention

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.

Struvite

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.

If your dog gets recurring urinary tract infections, thus predisposing it to a struvite bladder stone, it is important to examine it for abnormal anatomy of the vulva, for obesity, and problems with the urethral sphincter.

Calcium Oxalate

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.

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.

Blood calcium level

This calcium level at 12 is high (normal is up to 11.4), and it needs to be brought down to help decrease the chance of recurrence of calcium oxalate stones in the urinary bladder

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.

In non-Dalmatian dogs of these uroliths are caused by a PSS (liver shunt), 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 . 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 by performing urine culture and sensitivity tests every 3-6 months, and using antibiotics on a long term basis if needed.

Compound Uroliths

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 additional 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.

Dietary Information

Pet food manufacturers have dramatically increased their sophistication in treating bladder problems in dogs. 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.

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.

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