What is hydronephrosis?

Hydronephrosis is a condition in which one or both kidneys become swollen due to incomplete emptying of the urinary tract. It can be sudden or chronic, partial or complete, one-sided or bilateral. It can occur anywhere along the urinary tract from the opening of the kidneys to the ureters (draining the kidneys to the bladder), the bladder, and the urethra (draining the bladder). Problems with any of these structures may cause impaired emptying of the urinary system and back up of fluid and pressure.

If only one of the kidneys is affected, the condition is called unilateral hydronephrosis. If both kidneys are affected, it is called bilateral hydronephrosis.

Hydronephrosis may result in decreased kidney function. If not treated right away, permanent damage to the kidney or kidneys may occur, resulting in kidney failure.

Who gets hydronephrosis?

Hydronephrosis can occur in people of all ages. In children it is often due to structural changes in the body (anatomic abnormalities) present since birth or before. In young people, it is often due to kidney stones.

What causes hydronephrosis?

In adults, the conditions that most often cause hydronephrosis include:

  • Kidney stones: Stones that may become lodged in the kidneys or urinary tract.
  • Cancer: Tumors in the bladder, prostate gland, uterus or other organs that are part of or near the urinary tract may cause blockages that disrupt the flow of urine.
  • Benign prostatic hyperplasia (BPH): Enlargement of the prostate gland in men can cause pressure on the urethra, the tube that urine passes through before it leaves the body.
  • Having blood clots: Blood clots can develop in the kidney or ureter.
  • Narrowing or stricture of the urinary tract: This narrowing can be due to injury, infection, birth defects or surgery.
  • Nerve or muscle problems: These problems can affect the kidneys or ureters, such as from diabetes mellitus.
  • Urinary retention: Urine may be held inside the body due to an inability to empty the bladder.
  • Vesicoureteral reflux: This is a condition when urine flows backward from the bladder to the kidneys.
  • Uterocele: This is a condition where the lower part of the ureter may protrude into the bladder.

In women, hydronephrosis may occur as a result of:

  • Pregnancy: As the uterus expands, it can press on the ureters and block the flow of urine.
  • Uterine prolapse: A condition in which a woman's uterus (womb) sags or slips out of its normal position.
  • Cystocele (fallen bladder): A condition that occurs when the wall between a woman's bladder and her vagina weakens and allows the bladder to droop into the vagina.

What are the symptoms of hydronephrosis?

Symptoms of hydronephrosis usually depend on the cause. Often there are no symptoms. When symptoms occur, they can include:

  • Sudden or intense pain in the back or side
  • Nausea
  • Vomiting
  • Frequent or painful urination
  • Blood in the urine
  • Weakness or malaise
  • Fever due to a urinary tract infection
  • No major change in urine output although it may be decreased

Last reviewed by a Cleveland Clinic medical professional on 05/22/2019.


  • National Kidney Foundation. Hydronephrosis. Accessed 5/24/2019.
  • Martin Goldberg, MD, MACP, Ankush Gulati, MD, Patience Wildenfels, MD, Joseph E Scherger, MD, MPH. Obstructive uropathy [First Consult].
  • Merck Manual Consumer Version. Hydronephrosis. Accessed 5/24/2019.

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