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Hydronephrosis (Fluid Accumulation in the Renal Pelvis) in Dogs

Occurrence: rarer
Location of illness: Abdomen/pelvis

Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

Hydronephrosis in dogs is a condition in which excessive fluid accumulates in the renal pelvis. This accumulation can lead to kidney damage and hinder the normal flow of urine, ultimately leading to Kidney function impaired.

BASICS/CAUSES:

A dog’s kidneys have the important job of filtering waste products from the blood and forming urine, which then passes through the ureters into the bladder. The area of the kidney where the urine is collected before it flows into the ureters is called the renal pelvis. If the flow of urine is obstructed at any point, backflow can occur, leading to hydronephrosis.

One of the most common causes of hydronephrosis is an obstructionobstruction refers to the blockage or narrowing of a hollow organ or canal, which hinders the normal flow of liquids or gases. In dogs and cats, an obstruction can occur in the digestive tract, airways, or urinary tract and often requires immediate medical treatment. in the urinary tract. This can be caused by Nephrolithiasis (kidney stones), Tumors, injuries, or congenitalCongenital means "present from birth" and refers to characteristics or conditions that are already present at birth. This can include genetic disorders, developmental anomalies, or infections transmitted by the mother. malformations. These blockages prevent urine from flowing normally and lead to backflow, which puts pressure on and damages the kidneys.

Another cause may be a Urinary tract infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease., which leads to inflammation and Swelling, which in turn obstructs the flow of urine. Neurological disorders that impair control over bladder emptying can also indirectly lead to hydronephrosis.

The most important facts at a glance

Hydronephrosis in dogs is a condition in which fluid accumulates in the renal pelvis. This can be caused by ureteralUreteral refers to the ureter, which carries urine from the kidneys to the bladder. Ureteral problems in dogs and cats can impair urine flow and cause Pain. obstructions such as stones, tumors, or stricturesStrictures are pathological narrowings of tubes or ducts in the body that impede the normal flow of fluids or other substances. In dogs and cats, strictures can occur in the urethra, esophagus, or bile ducts and require medical treatment., but congenitalCongenital means "present from birth" and refers to characteristics or conditions that are already present at birth. This can include genetic disorders, developmental anomalies, or infections transmitted by the mother. anomalies of the urinary tract, prostate diseases, or severe infections can also play a role. Common symptoms include loss of appetite, Restlessness, Pain, increased thirst, and increased urination. Clinical examinations and imaging techniques such as ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. and X-rays are used for diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. to visualize the kidney structure. Blood and urine tests help to assess Kidney function impaired and identify underlying causes. Treatment depends on the cause of the hydronephrosis. Surgical removal may be necessary for obstructions, while infections are often treated with antibiotics. In severe cases, removal of the affected kidney may be necessary. The prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. depends on the cause and extent of kidney damage. Preventive measures include preventing Urinary tract infections through a balanced diet and adequate hydration. Regular veterinary examinations are important for early detection of problems. Research focuses on genetic predispositions, advanced diagnostic techniques, and new therapeutic approaches, including drug treatments and regenerative medicine. The role of nutrition is also being investigated to reduce the risk of developing hydronephrosis and positively influence the course of the disease.

Causes

UreteralUreteral refers to the ureter, which carries urine from the kidneys to the bladder. Ureteral problems in dogs and cats can impair urine flow and cause Pain. obstructions (stones, tumors, stricturesStrictures are pathological narrowings of tubes or ducts in the body that impede the normal flow of fluids or other substances. In dogs and cats, strictures can occur in the urethra, esophagus, or bile ducts and require medical treatment.)
CongenitalCongenital means "present from birth" and refers to characteristics or conditions that are already present at birth. This can include genetic disorders, developmental anomalies, or infections transmitted by the mother. anomalies of the urinary tract
Prostate diseases that obstruct urine flow
Severe Urinary tract infections

Symptoms

Very common symptoms:

Common symptoms:

The symptoms of hydronephrosis in dogs can vary depending on the severity of the condition. A common symptom is increased thirst and increased urination. The dog may also show Pain or discomfort, especially in the abdominalThe term “abdominal” refers to anything that concerns the belly or the abdomen. It is an adjectival expression used to describe the location, symptoms, or conditions that occur in the abdominal area. area.

Other signs may include Lethargy, loss of appetite, and Weight loss. In some cases, bloody or cloudy urine may occur. In severe hydronephrosis, the dog may also show signs of kidney failureRenal failure is a condition in which the kidneys can no longer adequately perform their function of filtering and excreting waste products from the blood. It can be acute or chronic and requires immediate medical treatment., such as Vomiting, DiarrheaDiarrhea refers to the condition of frequent, watery bowel movements, which can be a sign of infections, digestive disorders, or other health problems., and general weakness.

In advanced cases, the dog’s abdomenThe abdomen, also known as the abdominal cavity, is the part of the body located between the rib cage and the pelvis. It houses several important organs, including the stomach, liver, kidneys, intestines, and spleen. may appear visibly swollen due to the enlarged kidneys. It is important to pay attention to these symptoms and seek veterinary attention quickly if hydronephrosis is suspected.

Diagnosis

The diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of hydronephrosis begins with a thorough clinical examination by the veterinarian. The veterinarian will palpate the dog’s abdomenThe abdomen, also known as the abdominal cavity, is the part of the body located between the rib cage and the pelvis. It houses several important organs, including the stomach, liver, kidneys, intestines, and spleen. to look for enlarged kidneys and assess the dog’s general condition.

Imaging procedures are crucial for diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients.. Ultrasounds are particularly useful for visualizing the structure of the kidneys and determining whether there is fluid accumulation. X-rays can also be helpful in assessing the size of the kidneys and the course of the urinary tract.

In addition, blood and urine tests can be performed to assess Kidney function impaired and identify possible infections or other underlying causes. In some cases, a contrast study may be necessary to more accurately assess the patency of the urinary tract.

Therapy

The treatment for hydronephrosis depends on the underlying cause. If an obstructionobstruction refers to the blockage or narrowing of a hollow organ or canal, which hinders the normal flow of liquids or gases. In dogs and cats, an obstruction can occur in the digestive tract, airways, or urinary tract and often requires immediate medical treatment., such as a kidney stone, is the cause, surgical removal may be necessary to restore urine flow. In less severe cases, medications can be used to dissolve stones or treat infections.

For infections, antibiotics are often prescribed to reduce inflammation and normalize urine flow. If a neurological disorder is present, medications can be used to improve bladder control.

In severe cases where the kidney is severely damaged, a nephrectomy, or removal of the affected kidney, may be necessary. Dogs can live well with only one healthy kidney, provided the remaining kidney is functional.

Prognosis and follow-up care

The prognosis for a dog with hydronephrosis depends on the cause and extent of kidney damage. If the condition is detected and treated early, the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. can be favorable, especially if the underlying cause can be successfully resolved.

In cases where there is significant kidney damage or the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. is made late, the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. may be worse. ChronicChronic refers to a condition or disease that is long-lasting or permanent. Chronic diseases often develop slowly and can lead to persistent or recurring health problems over time. kidney damage can lead to permanent loss of function, which can affect the dog’s quality of life and life expectancy.

Regular veterinary check-ups and careful monitoring of Kidney function impaired are important to monitor the dog’s health and detect complications early.

Prevention

The preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. of hydronephrosis in dogs focuses on preventing Urinary tract infections and early detection of problems in the urinary tract. A balanced diet and adequate hydration can help reduce the risk of Nephrolithiasis (kidney stones) and infections.

Regular veterinary examinations are crucial for early detection of health problems. In dogs prone to urinary tract diseases, the veterinarian may recommend special diets or supplements to support urinary tract health.

Careful monitoring of the dog’s drinking habits and urination behavior can help detect early signs of problems. If changes are noticed, a veterinarian should be consulted immediately to clarify possible causes and intervene in a timely manner.

Outlook on current research

Hydronephrosis in dogs is an area of intense research to understand the causes and best treatment methods for this condition. Current studies focus on the genetic factors that may contribute to susceptibility to hydronephrosis. In particular, researchers are investigating whether certain breeds are more likely to develop hydronephrosis due to genetic predispositions. These genetic studies could lead to predictive tests in the long term that make it possible to identify at-risk dogs early and take preventive measures.

Another important area of research is the development of advanced imaging techniques for better diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of hydronephrosis. Traditionally, the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. has been made using ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. and X-rays, but new technologies such as magnetic resonance imaging (MRI)Magnetic resonance imaging is an imaging technique that uses strong magnetic fields and radio waves to create detailed images of the inside of the body. It is used in veterinary medicine to diagnose diseases of the brain, spine, and other organs. and computed tomography (CT)Computed tomography (CT) is an imaging technique that uses X-rays and computer technology to create cross-sectional images of the body. It enables a detailed view of bones, organs, and other structures and is used for the diagnosis of injuries, diseases, and for planning medical interventions. offer more detailed insights into the kidney structure and the underlying problems. These technologies enable a more accurate diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and thus more targeted treatment approaches.

Research into hydronephrosis also includes the development of new therapeutic approaches. In addition to surgical interventions, which are often necessary to eliminate the cause of the obstructionobstruction refers to the blockage or narrowing of a hollow organ or canal, which hinders the normal flow of liquids or gases. In dogs and cats, an obstruction can occur in the digestive tract, airways, or urinary tract and often requires immediate medical treatment., research is being conducted into drug treatments that could help reduce inflammation and pressure in the kidneys. Some studies are investigating the use of anti-inflammatory drugsAnti-inflammatory drugs are medications that reduce inflammation. They can be divided into nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids and are used in dogs and cats to reduce Inflammatory conditions and Pain. or diureticsDiuretics are medications that increase urine production in the kidneys to rid the body of excess salt and water. They are often used to treat high blood pressure, heart failure, and certain types of edema. to relieve symptoms and slow the progressionProgression refers to the advancement or worsening of a disease over time. It describes an increase in the severity or extent of the disease symptoms. of the disease.

Another promising research approach is regenerative medicine. This involves investigating whether stem cell therapies can help repair damaged kidney tissue and improve Kidney function impaired. These therapies are still in an early stage of development, but could play an important role in the treatment of hydronephrosis in the future.

Finally, the role of nutrition in the preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. and treatment of hydronephrosis is being investigated. Researchers are analyzing whether special diets or supplements can reduce the risk of developing hydronephrosis or positively influence the course of the disease. These studies could lead to dietary recommendations that support kidney health and reduce the risk of complications.

Frequently asked questions (FAQs)

What is hydronephrosis in dogs? Hydronephrosis is a condition in which fluid accumulates in the renal pelvis of a dog. This usually happens due to a blockage or narrowing of the urinary tract that prevents normal urine flow. This accumulation of urine can lead to Swelling of the kidneys and, in the worst case, Kidney function impaired.
What symptoms does a dog with hydronephrosis show? The most common symptoms include Lethargy, decreased appetite, Vomiting, increased thirst, and more frequent urination. In advanced cases, Weight loss and Pain in the abdominalThe term "abdominal" refers to anything that concerns the belly or the abdomen. It is an adjectival expression used to describe the location, symptoms, or conditions that occur in the abdominal area. area may occur. If hydronephrosis is suspected, it is important to consult a veterinarian.
How is hydronephrosis diagnosed in dogs? The diagnosis is usually made through a combination of clinical examination, blood and urine tests, and imaging procedures such as ultrasoundUltrasound refers to sound waves that are above the hearing threshold of the human ear. In medicine, ultrasound is used for diagnostic imaging procedures to visualize internal organs, tissues, and blood flow. or X-rays. These examinations help identify the cause of the obstructionobstruction refers to the blockage or narrowing of a hollow organ or canal, which hinders the normal flow of liquids or gases. In dogs and cats, an obstruction can occur in the digestive tract, airways, or urinary tract and often requires immediate medical treatment. and determine the severity of the condition.
What treatment options are available for hydronephrosis? Treatment depends on the cause of the hydronephrosis. In many cases, surgery may be required to remove the blockage. Antibiotics may be necessary for an infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease.. SupportiveSupportive refers to supportive treatments that aim to alleviate symptoms and improve quality of life without directly treating the underlying cause of the disease. therapies such as fluid administration and Pain management are also important to improve the dog’s well-being.
Can hydronephrosis be cured in dogs? The chances of recovery depend on the cause and progressionProgression refers to the advancement or worsening of a disease over time. It describes an increase in the severity or extent of the disease symptoms. of the disease. In cases where the cause can be successfully treated, there is a good prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop.. In more severe cases, especially if Kidney function impaired is severely impaired, the condition can become chronicChronic refers to a condition or disease that is long-lasting or permanent. Chronic diseases often develop slowly and can lead to persistent or recurring health problems over time..
How common is hydronephrosis in dogs? Hydronephrosis is a relatively rare condition in dogs. However, it can occur at any age and affect any breed. However, certain breeds appear to be more susceptible, possibly indicating genetic predispositions.
Can hydronephrosis be prevented in dogs? Complete protectionProtection refers to safeguarding against diseases or harm. In veterinary medicine, this can include protecting animals through vaccinations, the use of parasite control products, or providing a safe environment. is not always possible, but regular veterinary examinations and early treatment of Urinary tract infections or other diseases can reduce the risk. A balanced diet and adequate hydration also contribute to kidney health.
What complications can occur with hydronephrosis? Without treatment, hydronephrosis can lead to permanent kidney damage, kidney failureRenal failure is a condition in which the kidneys can no longer adequately perform their function of filtering and excreting waste products from the blood. It can be acute or chronic and requires immediate medical treatment., or infections. These complications can be life-threatening, which is why rapid diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment are crucial.
Is hydronephrosis painful in dogs? Yes, hydronephrosis can cause Pain, especially if the kidneys are severely swollen or an infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. is present. The Pain intensity can vary, and some dogs may show Behavioral changes or Restlessness as signs of discomfort.
Are there special diets for dogs with hydronephrosis? While there is no specific diet to cure hydronephrosis, veterinarian-recommended kidney diets can help reduce the strain on the kidneys. These diets typically have reduced proteinProteins are large molecules made up of amino acids and play an essential role in almost all biological processes. They are necessary for building body tissue, the function of the immune system, and as enzymes for metabolic reactions. and phosphate content and are designed to support Kidney function impaired.