Hydronephrosis

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Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

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Medical Editor:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Hydronephrosis describes the situation where the urine collecting system of the kidney is dilated. This may be a normal variant or it may be due to an underlying illness or medical condition.

Normally, the kidney filters waste products from blood and disposes of it in the urine. The urine drains into individual calyces (single=calyx) that form the renal pelvis. This empties into the ureter, a tube that connects the kidney to the bladder. The urethra is the tube that empties the bladder.

While obstruction or blockage is the most frequent cause of hydronephrosis, it may be due to problems that occur congenitally in a fetus (prenatal) or may be a physiologic response to pregnancy.

Technically, hydronephrosis specifically describes dilation and swelling of the kidney, while the term hydroureter is used to describe swelling of the ureter. Hydronephrosis may be unilateral involving just one kidney or bilateral involving both.

A complication of hydronephrosis is decreased kidney function. The increased pressure of extra fluid within the kidney decreases the blood filtration rate and may cause structural damage to kidney cells. This decrease in function is reversible if the underlying condition is corrected but if the hydronephrosis lasts many weeks, the damage may be permanent.

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

Ureter

• 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

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

Urethra

• 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

Ureter

• 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

Urethra

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

Examples of functional causes of hydronephrosis

Bladder

• 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.