- Hydronephrosis describes swelling of the kidney resulting from the inability of urine to drain from the kidney into the bladder.
- Hydroureter describes swelling of the ureter, the tube that connects the kidney to the bladder.
- The obstruction may occur at any level in the urinary collecting system from the kidney to the ureter to the bladder to the urethra.
- Depending on the level of the cause, hydronephrosis may be unilateral involving one kidney or bilateral involving both.
- The increased pressure caused by hydronephrosis potentially can compromise kidney function if it is not relieved in a reasonable period of time.
- Symptoms of hydronephrosis depend upon whether the swelling occurs acutely or progresses more gradually. If it is an acute obstruction, symptoms may include writhing pain, nausea, and vomiting.
- Treatment of hydronephrosis and hydroureter is aimed at restoring urine flow from the affected kidney.
What is hydronephrosis?
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 the blood and dispose 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.
Picture of the kidney and urinary system
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 maybe a physiologic response to pregnancy. A large percentage of pregnant women develop hydronephrosis or hydroureter. Experts think this is, in part, because of the effects of progesterone on the ureters, which decreases their tone.
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 that is not physiologic 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 often reversible if the underlying condition is corrected but if the duration is prolonged, the damage is often permanent.
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
- The inability to empty the bladder (urinary retention) for any reason may cause bilateral hydronephrosis.
- Urethral Stricture
- Urethral Valves
- Urethral cancer
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
- 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 backward from the bladder into the ureter. Prenatal hydronephrosis is an example, though it may occur at any time in life.
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