Unilateral hydronephrosis

Alternative names


Unilateral hydronephrosis occurs when a single kidney becomes distended or swollen due to a backup of urine. When both kidneys are involved, the condition is called bilateral hydronephrosis.

Causes, incidence, and risk factors

Hydronephrosis is a condition that occurs with a disease and is not a disease itself. Treatment and prognosis for unilateral hydronephrosis depend on the associated disorder.

Conditions that are often associated with unilateral hydronephrosis include the following:

  • Acute unilateral obstructive uropathy  
  • Chronic unilateral obstructive uropathy  
  • Vesicoureteric reflux (backflow of urine from bladder to kidney)  
  • Nephrolithiasis (kidney stones)  
  • Idiopathic hydronephrosis of pregnancy

Unilateral hydronephrosis occurs in approximately 1 in 100 people.


  • Flank pain  
  • Abdominal mass  
  • Nausea and vomiting  
  • Urinary tract infection  
  • Fever  
  • Dysuria  
  • Increased urinary frequency  
  • Increased urinary urgency

Note: Sometimes unilateral hydronephrosis does not have symptoms.

Signs and tests
Unilateral hydronephrosis is usually identified with tests such as the following:

  • Intravenous pyelogram (IVP)  
  • Isotope renography (radio-isotope scan of the kidneys)  
  • Ultrasound of the kidneys or abdomen  
  • CT scan of the kidneys or abdomen  
  • Abdominal MRI


A ureteral stent (which allows the ureter to drain) or nephrostomy tube (which allows the kidney to drain through the back, bypassing the ureter) will provide temporary relief of the obstruction. However, the underlying cause must be treated to cure this condition.

If signs and symptoms of an infection are present, antibiotics and prompt relief of urinary obstruction is mandatory. Patients who have only one kidney, who have immune-compromising disorders such as Diabetes or HIV, or who have received a transplant should be treated promptly.

If hydronephrosis is chronic, preventive antibiotics may be prescribed to decrease the risk of urinary tract infections.

Expectations (prognosis)

Prolonged hydronephrosis results in the eventual loss of kidney function.


If hydronephrosis is left untreated, the affected kidney may be permanently damaged. Renal insufficiency or renal failure is rare with unilateral hydronephrosis because the other kidney usually functions normally. However, if the patient has only one functioning kidney, renal failure will occur.

Calling your health care provider

Call your health care provider if you have prolonged or severe flank pain, or if you suspect hydronephrosis.


Prevention of the disorders associated with unilateral hydronephrosis will prevent this condition.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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