Hydronephrosis - Cause

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What causes hydronephrosis?

There are numerous causes of hydronephrosis that are categorized based upon the location of the swelling and whether the cause is intrinsic (located within the urinary collecting system), extrinsic (outside of the collecting system) or if it due to an alteration in function.

Examples of intrinsic causes of hydronephrosis


  • Kidney stone. Likely the most common reason to have unilateral hydronephrosis is a kidney stone that causes obstruction of the ureter. The stone gradually moves from the kidney into the bladder but if it should act like a dam while in the ureter, urine will back up and cause the kidney to swell. This would be classified as an intrinsic obstruction.
  • Blood clot
  • Stricture or scarring


  • Bladder cancer
  • Bladder stones
  • Cystocele
  • Bladder neck contracture


  • The inability to empty the bladder (urinary retention) for any reason may cause bilateral hydronephrosis.
  • Urethral stricture
  • Urethral valves

Examples of extrinsic causes of hydronephrosis


  • Tumors or cancers that compress the ureter and prevent urine flow. Examples include lymphoma and sarcoma, especially if they are located in the retroperitoneum, where the kidneys and ureters are located behind the sac that contains the bowel.
  • Retroperitoneal fibrosis
  • Ovarian vein syndrome
  • Cancer of the cervix
  • Cancer of the prostate
  • Pregnancy
  • Uterine prolapse
  • Scarring due to radiation therapy


  • Prostate hypertrophy or swelling is a common cause of urinary retention and subsequent hydronephrosis in males.
  • Prostate cancer

Examples of functional causes of hydronephrosis


  • Neurogenic bladder or the inability of the bladder to function properly occurs because of damage to the nerves that supply it. This may occur in brain tumors, spinal cord injuries or tumors, multiple sclerosis, and diabetes among other causes.
  • Vesicoureteral reflux where urine flows backwards from the bladder into the ureter. Prenatal hydronephrosis is an example, though it may occur at any time in life.
Return to Hydronephrosis

See what others are saying

Comment from: Lynne, 35-44 Female (Patient) Published: December 23

I fell on black ice on Wednesday and injured my wrist. This is the following Tuesday. I wanted to see what I should be expecting at present and if I am on schedule on healing or not. Guess it's time to see the doctor again.

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Comment from: saltydog69, 45-54 Female (Patient) Published: January 20

I have a single kidney and I have severe hydronephrosis. I have had a stent put in in the past but now the fluid is more severe than it was before. My doctor says I either have a kink or scar tissue that causes the hydronephrosis and the only way to fix it is cutting out part of the tube and placing it back together but says I am a high risk for the surgery since it is my only kidney and will not do the surgery.

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