What Is Hydronephrosis?
Hydronephrosis means a kidney has become swollen because urine is backing up inside it. Urine normally drains from each kidney through a thin tube called the ureter into the bladder. When something blocks that flow, pressure builds inside the kidney, stretches it and, over time, damages the tissue that filters blood.
Causes
- Ureteral stones: small stones lodged in the ureter, especially common in cats
- Bladder stones or urethral blockage: see dog bladder stones, cat bladder stones and cat urinary blockage
- Birth defects: such as an ectopic ureter
- Tumors of the bladder or ureter; see transitional cell carcinoma
- Accidental injury to a ureter during abdominal surgery, or scar tissue
Signs to Watch For
If only one kidney is blocked, the other often keeps working and there may be few signs at first. Watch for:
- Belly or back pain, a hunched posture
- Vomiting, poor appetite and lethargy
- Drinking and urinating more, or straining with little urine
- Blood in the urine
- Signs of kidney failure if both kidneys are affected; see dog kidney failure symptoms
Emergency warning
A pet, especially a male cat, that strains to urinate and produces nothing needs a vet the same day. A complete blockage can become life threatening within a day or two.
Diagnosis
Ultrasound is the main test: it shows the swollen kidney and often the stone or blockage. X-rays, blood tests for kidney values and a urine test fill in the picture. Some pets need a contrast study to trace exactly where the urine is stuck.
Treatment
- Fluids and medicines to help a small stone pass
- Surgery to remove a blockage, or placement of a stent or bypass device to keep urine flowing
- Treating infection if present
- Removing a kidney that is badly damaged and no longer working, if the other kidney is healthy
Pets that keep some lasting kidney damage are managed like chronic kidney disease, with diet and regular blood tests.
Frequently Asked Questions
Can a kidney recover from hydronephrosis?
Often yes, if the blockage is relieved quickly. The longer the kidney stays blocked, the more permanent damage it suffers.
Is hydronephrosis painful?
It can be, especially when it develops suddenly from a stone. Slow-developing cases may cause little obvious pain.
How common is it in cats?
Ureteral stones have become a common cause of hydronephrosis in cats, so vets often check the kidneys by ultrasound in cats with rising kidney values.
If your pet strains to urinate, has belly pain or blood in the urine, get them checked promptly. Find a veterinary clinic near you for an exam.