What is hydronephrosis?

Hydronephrosis is a condition in which one or both kidneys become swollen due to the build-up of excess fluid. Each kidney consists of two parts. One part filters blood to remove excess water, salt, and waste products. The other part collects urine. When the part of the kidney that collects urine becomes blocked, the build-up causes swelling.

In addition to the kidneys, the urinary system consists of two ureters, the bladder, and the urethra. Problems with any of these structures may cause fluid to flow backward into the kidney.

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. If the condition occurs before birth, it is called fetal or antenatal hydronephrosis.

What causes hydronephrosis?

There are many causes of hydronephrosis. In adults, the conditions that most often cause hydronephrosis include:

  • Kidney stones—Salts and minerals that are present in urine can form small hard 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.

Other possible causes of hydronephrosis include:

  • Blood clots in the kidney or ureter
  • Narrowing or stricture of the urinary tract due to injury, infection, birth defects or surgery
  • Nerve or muscle problems that affect the kidneys or ureters
  • Urinary retention due to an inability to empty the bladder
  • Vesicoureteral reflux, when urine flows backward from the bladder to the kidneys
  • Uterocele, when 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 may include:

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