Stones in Dogs: Bladder and Urethra

Bladder and urethral stones in dogs, or lower urinary tract urolithiasis, are among the most common urological problems. Stones are dense mineral deposits that form in the urine under certain conditions and, over time, can reach significant sizes or form large clusters. [1]

In some dogs, stones remain asymptomatic for a long time and are discovered incidentally during an ultrasound or x-ray. In other cases, they cause significant symptoms: frequent, painful urination, blood in the urine, licking of the perineum, and episodes of urination in the house. A particularly dangerous situation occurs when a stone blocks the urethra and urine stops flowing. This is a life-threatening condition. [2]

It's important to understand that bladder stones and urethral stones are manifestations of the same problem, but with different degrees of severity. Bladder stones are more likely to cause pain and bleeding, but still allow urine to pass. Stones lodged in the urethra, especially in male dogs, quickly lead to acute urinary retention, elevated blood potassium levels, intoxication, and can progress to severe renal and cardiac failure within hours. [3]

Modern veterinary medicine has a wide range of diagnostic and treatment methods for urolithiasis. Depending on the type of stone and its location, dietary dissolution, minimally invasive removal through the bladder, hydraulic percussion lavage, endoscopic techniques, and classical surgery with an open bladder may be used. The choice of approach is determined by the type of stone, its size, the presence of obstruction, and the dog's overall condition. [4]

With proper diagnosis and a comprehensive approach, most dogs with stones have a good chance of recovery, but the risk of recurrence remains high. Therefore, it is important not only to remove existing stones but also, if possible, to modify the conditions that contributed to their formation: diet, fluid intake, urination frequency, and control of underlying medical conditions. [5]

Table 1. Stones in the bladder and urethra in dogs: the main thing

Question	Short answer
What is this	Mineral stones in the bladder or urethra
What is dangerous?	Pain, blood in the urine, risk of complete obstruction and rupture of the bladder
What stones are most common?	Struvite and oxalate, less often urate, cystine, silicate
Are surgeries always necessary?	No, some stones can be dissolved or removed minimally invasively.
Can it be prevented?	Yes, with the help of diet, plenty of fluids and control of concomitant diseases

Types of stones and their characteristics

Several main types of urinary stones have been described in dogs. The most common are struvite stones, composed of magnesium ammonium phosphate, and calcium oxalate stones. Less common are urate, cystine, silicate, and mixed stones, which combine several mineral components. [6]

Struvite stones in dogs are most often associated with urinary tract infections (UTIs), caused by bacteria that break down urea and alkalize the urine. Under these conditions, struvite crystals quickly form and stick together, forming stones. An important feature of struvites in dogs is that they can often be dissolved with a special diet and simultaneous treatment of the infection. [7]

Calcium oxalate stones, on the other hand, typically form in sterile, non-infectious urine, with high urine concentrations and excess calcium and oxalate. They do not respond to a solubility diet, so the only treatment is physical removal of the stones and subsequent prevention of recurrence. This type of stone is associated with a high recurrence rate after treatment. [8]

Less common types include urate and cystine stones. Urate stones are often associated with congenital metabolic disorders or portocaval shunts, especially in certain breeds, such as Dalmatians. Cystine stones arise from inherited disorders of the transport mechanisms in the renal tubules and are more common in male dogs of certain breeds. Silicate stones are rare and are associated with feeding habits and regional factors. [9]

Of practical importance is the distinction between stones located in the bladder and those lodged in the urethra. Bladder stones more often cause chronic discomfort and recurrent inflammation, while urethral stones lead to acute obstruction, requiring emergency measures to restore urine flow. Most urethral stones initially form in the bladder and then migrate. [10]

Table 2. Main types of urinary stones in dogs

Type of stone	Features of formation	Possibility of dissolution
Struvite	Often associated with infection and alkaline urine	Dietary and drug therapy are usually possible.
Calcium oxalate	Sterile concentrated urine, excess calcium and oxalate	Does not dissolve, requires physical removal
Urate	Metabolic disorders, portosystemic shunts	Partial dietary correction and medication support are possible.
Cystine	Hereditary disorders of amino acid transport	A combination of surgery and diet is often required.
Silicate	Rare, possible dietary relationship	Treatment is based on removal and specific prevention.

Causes and risk factors

The formation of stones in the bladder and urethra is a multifactorial process. The composition of urine and its concentration play a crucial role. When urine is highly mineralized, crystals form more easily and form aggregates. This can be caused by insufficient water intake, infrequent urination, and excess amounts of certain minerals and protein in the diet. [11]

Urinary tract infection, especially in female dogs, is a key factor in the development of struvite stones. Bacteria that produce the enzyme urease break down urea into ammonia, increasing the pH of the urine, and under these conditions, struvite crystals actively form. Without treatment of the infection and changes in the composition of the urine, these stones can form and enlarge very quickly. [12]

Gender and breed also influence the risk. Female dogs are more likely to suffer from infectious struvite stones due to their anatomical features: a short and wide urethra, with the external opening located close to the anus. Male dogs are more likely to experience urethral obstruction because their urethra is longer and has curves where stones can become lodged. Some breeds are predisposed to certain types of stones due to inherited metabolic characteristics. [13]

Age and underlying medical conditions also play a role. Calcium oxalate, urate, and mixed stones are more commonly diagnosed in adult and older dogs, especially in the setting of endocrine disorders, chronic kidney disease, or portosystemic shunts. In young animals, hereditary or breed-specific forms of urolithiasis associated with defects in the transport of substances or enzymes are common. [14]

Finally, external and controllable factors play a significant role: diet type, amount of dry food in the diet, level of physical activity, free access to water, and walking schedule. Irregular walking and prolonged holding lead to urine stagnation in the bladder, giving crystals more time to grow and aggregate into stones. [15]

Table 3. Main groups of risk factors for urolithiasis

Group of factors	Examples
Urine composition disorders	High mineral concentration, alkaline or highly acidic urine
Infections	Ascending bacterial bladder infections, especially in female dogs
Gender and breed	Male dogs are more prone to obstruction, and some breeds are more prone to certain types of stones.
Systemic diseases	Endocrine disorders, portosystemic shunts, chronic kidney disease
Lifestyle and diet	Lack of water, infrequent walks, unbalanced diet, excess dry food

How stones are formed: pathogenesis

Stone formation begins with crystals. When the concentration of certain substances in urine exceeds their solubility threshold, they begin to precipitate as microscopic crystals. If the urine is sufficiently dilute and excreted frequently, many crystals are flushed out before they have time to coalesce into anything larger. However, with high concentrations and stagnant urine, the crystals have time to coalesce. [16]

Crystal formation is influenced by the pH of the urine. Struvite forms best in alkaline urine, while many other crystals form best in more acidic urine. Therefore, an infection with urease-positive bacteria, which alkalizes the urine, creates near-ideal conditions for struvite stones. For calcium oxalate stones, the degree of saturation of the urine with calcium and oxalate is more important than the pH, although excessive acidification of the urine may increase the risk of this particular type of stone. [17]

Crystals don't always form stones. To do so, they require a matrix, a kind of "scaffold" of organic substances: proteins, cellular debris, bacteria, and mucus. Crystals settle and adhere more easily to such a matrix, forming dense aggregates. Therefore, chronic bladder inflammation, epithelial damage, and the presence of bacteria further increase the risk of large stones forming. [18]

As the stone grows, it can become heavy enough to mechanically irritate the bladder lining. This causes local inflammation, blood in the urine, and increased mucus and protein secretion, further fueling the stone's growth. It's a vicious cycle: the stone causes inflammation, and the inflammation provides the material for further stone growth. [19]

Small stones and their fragments can migrate into the urethra. If the lumen of the urethra is wide enough, some of them pass in the urine. If the stone is larger than a critical diameter, it becomes lodged, causing partial or complete obstruction. Due to the structural features of the urethra, this occurs more frequently in male dogs than in females and requires immediate intervention. [20]

Table 4. Simplified diagram of stone formation

Stage	What's happening
Urine supersaturation	The concentration of minerals exceeds the solubility threshold
Crystal formation	Precipitation of salts in the bladder
The emergence of the matrix	Inflammation, bacteria and proteins provide a "framework" for the crystals
Stone growth	Layers of crystals and matrix grow around the core
Migration and obstruction	Small stones or fragments enter the urethra and can block it.

Clinical signs and course of the disease

In many dogs, clinical signs are associated with irritation of the bladder lining. The animal begins urinating more frequently in small amounts, stands for a long time in the urination position, and produces only a small amount of urine. Pain during urination, restlessness, whining, and licking of the vulva or prepuce may occur. Owners often notice urination in a previously housetrained dog. [21]

Blood in the urine is a very characteristic sign. Urine may be pink, red, or streaked with blood; sometimes blood is only visible at the end of urination or on light-colored bedding or snow. However, the absence of blood does not rule out the presence of stones, especially in the early stages or with small stones. [22]

Some dogs with small stones may not show any noticeable symptoms for a long time. The stones are discovered incidentally during an examination for another reason. This doesn't mean the problem is harmless: under certain conditions, small stones can become dislodged, enter the urethra, and quickly cause obstruction. [23]

Acute urethral obstruction manifests itself with frequent but unsuccessful attempts to urinate, marked straining, groaning, and restlessness. The abdomen may become painful and distended due to an overflowing bladder. Signs of intoxication later develop: lethargy, refusal to eat, vomiting, loss of coordination, and, in severe cases, signs of a life-threatening condition. [24]

In chronic cases, recurrent episodes of cystitis, periodic exacerbations with blood in the urine, and episodes of partial obstruction followed by temporary relief are possible. Against this background, it is easy to miss the gradual deterioration of kidney function and the development of persistent infections, so any recurrence of symptoms requires careful attention. [25]

Table 5. What owners most often complain about when they have stones

Sign	What can it talk about?
Frequent urination in small amounts	Irritation of the bladder mucosa, decreased capacity of the organ
Pain and whining when urinating	Inflammation, spasm and mechanical irritation by stones
Blood in urine	Damage to the bladder wall and urethra
Urination in the house	Inability to bear the pain and frequent urges
Complete absence of urine when attempting to urinate	Possible obstruction requiring immediate assistance

Diagnostics

Diagnosis begins with a detailed owner interview and a clinical examination. The doctor will determine the duration and nature of symptoms, any previous urological problems, dietary habits, and the presence of systemic diseases. During the examination, the condition of the mucous membranes and the degree of dehydration are assessed, the bladder is palpated, and sometimes a rectal examination is performed to evaluate the prostate in males and the structure of the pelvic area. [26]

Urine tests play a key role. A general analysis allows for the assessment of specific gravity, urine pH, and the presence of protein, blood, crystals, and bacteria. Crystalluria does not always indicate the presence of stones, but it does provide clues about the type of mineral composition and the direction of abnormal urine values. If an infectious component is suspected, a urine culture and antibiotic susceptibility testing are performed. [27]

Radiography and ultrasound are used to visualize stones. Most struvite and calcium oxalate stones are clearly visible on standard radiographs as dense formations within the bladder or urethra. Some types of stones, such as urate and cystine stones, are less contrasting and are better visualized with ultrasound. These methods often complement each other. [28]

In complex or controversial cases, particularly where multiple stones, structural anomalies, or tumors are suspected, more advanced imaging techniques, such as contrast studies and computed tomography, can be used. These techniques help more accurately assess the number and location of stones, as well as the condition of the bladder wall and adjacent structures, which is important for choosing a removal method. [29]

The final stone type can only be reliably determined after laboratory analysis. For this purpose, the removed stone is sent to a specialized laboratory, where its mineral composition is quantitatively determined. This data is used to select a diet, assess the risk of recurrence, and develop a personalized prevention plan. [30]

Table 6. Basic diagnostic steps for suspected stones

Stage	Target
History taking and examination	Assessing the severity of the condition, identifying risk factors and concomitant diseases
General urine analysis	Confirmation of inflammation, pH determination, detection of crystals and blood
Urine culture	Diagnosis of the infectious component and selection of antibiotics
X-ray and ultrasound examination	Visualization of stones, assessment of their quantity, size and location
Analysis of removed stones	Precise stone type for personalized prevention

Urethral obstruction emergency care

Complete or near-complete obstruction of the urethra is an emergency. First and foremost, it's important to quickly assess the animal's overall stability: level of consciousness, respiration, heart rate, and signs of shock. At the same time, carefully palpate the bladder: a full, tense bladder, accompanied by no urine output during attempts to urinate, indicates obstruction. [31]

The first therapeutic measure for severe urinary retention is to restore urinary flow or temporarily reduce bladder pressure. Clinically, this is achieved by catheterizing the bladder under sedation or anesthesia and either retrograde irrigation of the urethra, which forces small stones back into the bladder, or by temporary bladder puncture if catheterization is not immediately possible. [32]

Simultaneously, the patient is stabilized with infusion therapy, correction of electrolyte imbalances, especially hyperkalemia, and pain relief. With prolonged obstruction, acid-base balance and cardiac dysfunction develop, so special infusion regimens, medications to correct arrhythmias, and electrocardiogram monitoring are used if necessary. [33]

Once the urethra is cleared, further treatment is decided. If the stone has been successfully displaced back into the bladder, its removal is planned using one of several methods: surgical, minimally invasive, or dietary, depending on the suspected composition. Leaving large stones in the bladder and only periodically "flushing" the urethra is unacceptable, as the risk of re-obstruction remains high. [34]

In severe, recurring cases, especially those with anatomical peculiarities, the creation of a permanent or temporary bypass for urinary drainage (ureterostomies, urethrostomies, and other specialized surgeries) may be considered. These interventions require a highly skilled surgeon and careful discussion with the owner, as they alter the dog's lifestyle and require special care. [35]

Table 7. Basic steps in acute obstruction

Step	Target
Quick assessment of the condition	Detection of shock, severe intoxication, life-threatening conditions
Providing temporary urine drainage	Catheterization or puncture of the bladder
Blood stabilization	Correction of electrolytes, acid-base balance, pain relief
Retrograde canal irrigation	Moving the stone back into the bladder, if possible
Planning stone removal	Selecting a method to eliminate the cause of obstruction

Methods of stone removal

Once the condition has stabilized, the main goal is to completely remove the stones. There are several approaches, the choice of which depends on the size, number, location, and expected composition of the stones, as well as the availability of equipment and the physician's experience.

The most traditional method remains surgical incision of the bladder and stone removal. This procedure is relatively simple in technique, allows for visual inspection of the bladder cavity, and removal of all visible stones. However, any surgery is associated with risks, and scar tissue and suture material in the bladder wall can contribute to recurrent stone formation. [36]

In recent years, minimally invasive techniques have been rapidly developing. These include the removal of small stones by forced urination under general anesthesia (urohydropropulsion), endoscopic extraction using special baskets and forceps, and laser stone fragmentation followed by removal of the fragments. These methods reduce trauma to the bladder wall and lower the risk of postoperative complications, but require specialized equipment and training. [37]

Some struvite stones can be dissolved with medication and diet. This involves placing the animal on a special diet that reduces magnesium and phosphorus levels, acidifies the urine, and ensures a low specific gravity. Concurrently, infection is treated based on culture results. With proper treatment, many struvite stones shrink and disappear without surgery, although the process takes weeks or months and requires regular monitoring. [38]

Calcium oxalate, urate, cystine, and some other types of stones are virtually insoluble. In these cases, diet and medication are used primarily to prevent recurrence, while the stones themselves are removed mechanically. The choice between surgery and minimally invasive methods depends on the size and number of stones, anatomical features, and equipment availability. [39]

For multiple or recurrent urethral obstructions, particularly in narrow areas, surgical dilation or creation of a new urinary drainage site may be necessary. Such procedures reduce the risk of obstruction but require careful long-term monitoring and strict adherence to care and prevention recommendations. [40]

Table 8. Basic methods of stone removal

Method	Pros	Restrictions
Open bladder surgery	Accessibility, ability to remove large and multiple stones	Surgical trauma, risk of recurrence, requires anesthesia
Urohydropropulsion	A minimally invasive method for removing small stones	Requires specific stone sizes and experience, not suitable for large stones
Endoscopic extraction and laser fragmentation	Minimal trauma, precision, fast recovery	Requires equipment and training and is not suitable for all patients.
Dietary and medicinal dissolution	Without surgery, especially for struvite stones	Cannot be used for certain types of stones and obstructions, requires time and discipline
Urinary flow modification surgeries	Reduce the risk of recurrent obstruction	Complex interventions that change the dog's lifestyle and require specialized care

Prevention and lifelong monitoring

Even after successful stone removal, a significant proportion of dogs develop new stones over time. Therefore, the current approach views urolithiasis as a chronic condition requiring lifelong monitoring and active prevention. [41]

The basic principle of prevention for all types of stones is maintaining well-diluted urine. This is achieved by increasing the proportion of wet food, adding water to dry food, providing constant access to fresh water, and encouraging more frequent urination through regular walks. Some recommendations focus on achieving a specific gravity of urine below approximately 1.020 in dogs to reduce the risk of crystallization. [42]

The next level is diets tailored to the type of stone. For struvite stones, diets with reduced magnesium and phosphorus levels are used, gently acidifying the urine and promoting the dissolution or prevention of new stones. For calcium oxalate stones, on the other hand, excessive acidification and excess protein are avoided, and a moderate pH and low calcium and oxalate concentrations are sought. Urate and cystine stones require a separate approach, with protein and purine restriction and, if necessary, the use of special medications. [43]

Correction and monitoring of concomitant pathologies is essential: endocrine disorders, portosystemic shunts, and chronic infections. In dogs with struvite stones, timely detection and treatment of urinary tract infections is crucial, including by culture, especially in cases of recurrence. In some cases, routine urine monitoring and periodic bladder imaging are recommended for early detection of new stones. [44]

In addition to diet, specific supplements to support bladder health, active walking regimens, and general measures to maintain a healthy weight and physical activity are discussed. Excess weight and inactivity contribute to urinary congestion, while adequate activity and regular walking help reduce the risk of recurrence. [45]

Table 9. Main areas of prevention

Direction	Specific measures
Urine dilution	Plenty of drinking water, wet food, water with dry food, regular walks
Specialized nutrition	Diets tailored to the type of stones, with controlled minerals and protein intake
Infection control	Regular urine tests, culture if necessary, timely treatment
Correction of underlying diseases	Treatment of endocrine and metabolic disorders, portosystemic shunts
Lifestyle	Maintaining a normal body weight and sufficient physical activity

Complications and prognosis

The main complications of bladder and urethral stones are related to obstruction and chronic inflammation. Repeated episodes of complete or partial obstruction lead to damage to the bladder wall, risk of bladder rupture, and acute renal failure. Even a single episode of severe urinary retention can leave a significant impact on kidney function. [46]

Chronic inflammation and recurrent urinary tract infections increase the risk of antibiotic-resistant bacterial strains, leading to thickening of the bladder wall, decreased bladder elasticity, and a chronic decline in the animal's quality of life. In some dogs, these conditions contribute to the progression of chronic kidney disease. [47]

The prognosis depends on several factors. For small, unobstructed struvite stones, with timely treatment and strict dietary adherence, the prognosis is usually favorable. For calcium oxalate, urate, and cystine stones, a good short-term prognosis is reported after removal, but a high risk of recurrence is emphasized. [48]

In severe obstruction, especially if it has persisted for a long time before presentation, the prognosis is guarded because the outcome is influenced by the extent of damage to the kidneys and cardiovascular system. Severe systemic diseases, advanced age, and the presence of other serious pathologies can also limit the possibilities of active intervention and worsen the prognosis. [49]

It's important to remember that proper diagnosis, the right stone removal method, and strict adherence to preventative recommendations allow many dogs to live long and active lives. Key factors include communication between the owner and the treating veterinarian, regular monitoring, and a willingness to adjust the plan as the animal's condition changes. [50]

Table 10. Factors influencing outcome

Factor	Impact on prognosis
Type and composition of stones	Struvite in dogs is easier to treat with the right tactics, calcium oxalate is prone to relapse
Presence and duration of obstruction	The longer you hold your urine, the higher the risk of irreversible damage.
Concomitant diseases	Endocrine and renal pathologies may worsen the outcome
Choice and completeness of treatment	Removing all stones and then monitoring them is better than half measures.
Compliance with preventive measures	Regular urine testing, diet, and exercise regimen reduce the risk of relapse.

Frequently asked questions from owners

Can a stone "dissolve on its own" without treatment?

In rare cases, very small stones or sand may pass spontaneously in the urine, especially if fluid intake is improved. However, it's unrealistic to expect complete spontaneous disappearance of stones that are already visible on ultrasound or X-ray. Without targeted treatment, the risk of obstruction and chronic inflammation remains.

Is it dangerous to wait if the dog only urinates a little more often and sometimes there is blood in the urine?

Yes. Even if your dog appears relatively healthy, repeated episodes of frequent, painful urination and blood in the urine require investigation. These could indicate stones, an infection, or another urinary tract disorder. Early detection significantly simplifies treatment and reduces the risk of emergency situations.

Is it possible to treat stones with diet alone, without surgery?

Sometimes yes, but not always. Struvite stones in dogs can often be dissolved with special diets and infection treatment. However, for calcium oxalate, urate, and cystine stones, dietary dissolution is usually impossible. In these cases, diet is used to prevent recurrence, and the stones themselves must be mechanically removed.

Do all dogs with bladder stones need surgery?

The decision depends on the type of stones, their number and size, the presence of obstruction, and the available treatments. In some cases, minimally invasive removal or dissolution is possible. However, leaving large stones in the bladder for long periods is unsafe, as there is a persistent risk of relapse, obstruction, and chronic inflammation.

How often should I check my dog after stone treatment?

The specific schedule is determined by the doctor, but typically, after stone removal or dissolution, follow-up urine tests and imaging are performed several months later, and then periodically throughout life, especially in breeds and animals at high risk of recurrence. If any urinary tract symptoms appear, it is advisable to undergo an examination immediately.