If You Notice Abnormalities in Your Dog’s Urine — Causes of Hydronephrosis and When to Visit the Vet

KidneyDiseasesMeongsiljang Veterinary Advisory Board

Hydronephrosis in dogs is a condition in which urine accumulates and causes the kidneys to swell, making early detection and appropriate treatment essential. The causes can vary, including urinary tract obstruction, genetic abnormalities, and trauma.

What Is Canine Hydronephrosis?

An ultrasound image showing the puppy's kidneys appearing swollen.

Canine hydronephrosis is a condition in which urine accumulates in the kidney, causing the renal pelvis to dilate and the kidney to swell. It occurs when there is an obstruction anywhere along the urinary tract. If this condition persists, it can damage kidney tissue and, in severe cases, lead to impaired kidney function. Early symptoms are often subtle, making early detection difficult, but characteristic signs may include an enlarged kidney that is painful to the touch. Because the condition can progress acutely, prompt diagnosis and treatment are essential. Early management plays a crucial role in preserving kidney function. - Urinary stasis in the kidney: A condition in which the urine drainage pathway is blocked, causing the renal pelvis to dilate and the kidney to swell. - Urinary tract obstruction: Often caused by stones, tumors, or inflammation, and is the most common cause. - Functional impairment: Prolonged urinary stasis can lead to damage of kidney cells and a decline in kidney function. - Early detection: Because symptoms may be mild, regular veterinary check-ups are important. - Acute progression: In acute hydronephrosis, the kidney swells rapidly and may show signs of pain when touched.

What Are the Main Causes of Hydronephrosis?

The primary cause of hydronephrosis in dogs is urinary tract obstruction, which occurs when lesions such as stones, tumors, inflammation, or polyps block the pathway for urine to exit. In male dogs, lower urinary tract issues, such as those caused by prostate disease, can lead to obstruction. Additionally, certain breeds may have genetic kidney structural abnormalities, such as renal dysplasia or polycystic kidney disease, which can be confirmed via ultrasound. Trauma, repeated urethral catheterization, or foreign bodies within the urinary tract can also cause obstruction. However, hydronephrosis most commonly results from acquired urinary tract obstruction. - Stones: Urinary stones (uroliths) within the urinary tract are a leading cause of obstruction by blocking the urine pathway. - Tumors and Polyps: Lesions such as tumors or polyps developing within the urinary tract can cause obstruction. - Inflammatory Response: Severe urinary tract infections or inflammation can cause swelling that blocks urine flow. - Structural Abnormalities: Genetic kidney malformations, such as renal dysplasia or polycystic kidney disease, have been reported in certain breeds. - Trauma: External impact or repeated urethral catheterization can damage the urinary tract.

An anatomical diagram showing a urinary tract obstruction in a dog caused by uroliths

What Are the Main Symptoms of Hydronephrosis?

In the early stages of canine hydronephrosis, symptoms may be absent or very mild. However, as the condition progresses, signs such as decreased appetite, vomiting, abdominal pain, difficulty urinating, and frequent urination may appear. Behaviors like clutching the belly or crying out are strong indicators of pain. Swelling in the kidney area may also be noticeable. If left untreated for an extended period, this condition can lead to dehydration, abnormal blood test results, and even kidney failure. - Decreased appetite: Dogs often refuse food due to impaired digestive function. - Recurrent vomiting: This occurs because toxins accumulate as kidney function declines. - Abdominal pain: The swollen kidneys create pressure, causing discomfort and pain. - Difficulty urinating: Urinary tract obstruction prevents proper urination. - Kidney swelling: This is a characteristic finding clearly visible on ultrasound examination.

A photo of a puppy showing signs of abdominal pain

Signs That Require an Immediate Vet Visit

If your dog suddenly loses its appetite, vomits repeatedly, or cries out while clutching its abdomen, it may be a sign of severe pain caused by significant swelling of the kidneys. Please consult a veterinarian immediately.

How Is Hydronephrosis Diagnosed?

Hydronephrosis in dogs is most accurately diagnosed through ultrasound, which allows direct visualization of the swollen kidney and the exact location of the urinary tract obstruction. Blood tests assess kidney function markers (creatinine and BUN), while urinalysis evaluates for infection and protein leakage. Radiographs or CT scans may also be performed if necessary. Accurately identifying the underlying cause during the diagnostic process is key to effective treatment. - Ultrasound: Enables real-time observation of kidney swelling and urinary tract obstruction. - Blood tests: Confirm kidney function impairment through measurable values. - Urinalysis: Identifies the presence of infection, proteinuria, or hematuria. - Imaging studies: CT scans or radiographs provide supplementary confirmation of complex obstruction causes. - Cause analysis: Precisely determining the cause of obstruction guides treatment decisions.

Ultrasound image showing fluid accumulation in a dog’s kidneys

What Are the Treatment Options for Hydronephrosis?

Treatment for hydronephrosis depends on the underlying cause. If kidney stones are the culprit, they are removed via surgery or endoscopy. If a tumor is suspected, a biopsy is performed first, followed by consideration of surgery or radiation therapy. As a temporary measure, a drainage tube may be inserted into the kidney to allow urine to drain. After surgery, medications such as antibiotics, pain relievers, and drugs to promote urination are necessary. Regular check-ups remain essential even after treatment. - Stone removal: Kidney stones are removed through endoscopy or surgery. - Surgical treatment: Surgery is required for tumors or severe obstructions. - Drainage tube insertion: A tube is inserted into the kidney for temporary urine drainage. - Medication: Medications to prevent infection and relieve pain are essential. - Preventing recurrence: Regular check-ups help prevent recurrence even after addressing the underlying cause.

A surgical scene showing the insertion of a renal drainage tube into a dog.

Key Points for Home Care

After surgery, it’s essential to follow your veterinarian’s instructions and administer all prescribed medications. This includes pain relievers, antibiotics, and medications to promote urination, all given at the correct dosage and timing. For meals, offer small, frequent portions and carefully manage salt and protein intake. Ensure your pet stays adequately hydrated to avoid putting extra strain on the kidneys. Regular check-ups and urine tests are necessary to monitor their condition. - Medication: Always follow your vet’s instructions for administering medications. - Dietary Management: Control salt and protein intake to reduce the burden on the kidneys. - Hydration: Encourage sufficient water intake without overdoing it. - Regular Check-ups: Schedule an ultrasound every three months post-surgery to monitor progress. - Observation Points: Keep a consistent record of appetite, urination patterns, and any signs of abdominal pain.

A puppy eating food that is good for kidney health.

Breed-Specific Precautions and Preventing Recurrence

Certain breeds are prone to hereditary kidney abnormalities, such as renal dysplasia or polycystic kidney disease, so extra attention to kidney and urinary tract health is essential. Regular check-ups, including urinalysis and ultrasound imaging, are crucial for early detection of any issues. Even after surgery or treatment, it’s advisable to have ultrasounds performed at intervals recommended by your veterinarian to monitor for recurrence.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is polydipsia treatable?

Most cases can be fully recovered once the underlying cause is removed. Early diagnosis and appropriate treatment are key.

How should I care for my dog after surgery?

After surgery, it’s important to limit your pet’s activity, carefully manage the drainage tube, and ensure they take their medications as prescribed. Always follow your veterinarian’s instructions.

Can hydrocephalus recur?

There is a possibility of recurrence. Regular check-ups are important if the cause of the obstruction remains or if there are structural abnormalities.

Is hydrocephalus only seen in dogs?

Urinary tract obstruction can occur in adult dogs as well, often due to bladder stones or tumors. While certain breeds have been reported to have hereditary abnormalities in kidney structure, acquired urinary tract obstruction is the most common cause.

What is the prognosis for hydronephrosis?

If the underlying cause is removed and treatment is started early, most pets make a full recovery. However, if the kidney damage is severe, it can progress to chronic kidney disease.

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References

[1] Plumb's Veterinary Drug Handbook, 9th Edition, 2022

[2] Notes on Canine Internal Medicine, 4th Edition, 2018

[3] BSAVA Manual of Canine and Feline Dermatology, 4th Edition, 2019