Blocked Ureter (Obstruction) Causes and Symptoms

Our body excretes metabolic waste products through urine, which is formed in two bean-shaped organs known as kidneys. The urine formed in each of the kidneys flows down into a single urinary bladder through two muscular tubes known as ureters. Urine in the urinary bladder is finally expelled out of the body through the urethra. When considering diseases of the urinary system, people mainly focus on the kidneys and the bladder. Only scant attention is paid to the ureters. However, problems with the ureters can adversely affect the functioning of the kidneys, and could even be lethal.

The length of each ureter is approximately 30 centimeters. This muscular tube emerges from the kidney at a region known as the hilus. The ureters from the two kidneys then pass in close contact with the common iliac arteries, traverse the lateral abdominal wall and finally enter the pelvis to join the urinary bladder. Even after reaching the urinary bladder, the uterers run a short distance into it.

The ureters are long, thin, and muscular tubes with a nearly constant diameter throughout their course from the kidneys to the urinary bladder. However, there are three regions where the lumen of ureters becomes relatively narrow. These three areas of relative constriction are the regions where:

  • the ureter communicates with the renal pelvis,
  • the ureter crosses the inlet of the pelvic brim, and
  • the ureter penetrates the urinary bladder.

These three areas of constriction are medically important because they are potential sites for obstruction to urine flow through the ureter. For example, kidney stones passing out into the ureter may get lodged at these points of constriction, causing a partial or complete blockage of urine flow.

Partial and Complete Obstruction of Ureters

Most cases of blocked ureter affect only one of the two ureters. This allows the unaffected kidney and ureter to compensate for the blockage and maintain normal urinary output. In some cases, both the ureters may get blocked. This is rare, but has very serious consequences due to complete blockage of urinary flow exerting pressure on the kidneys.

The obstruction of ureters may either be partial or complete. In case of partial blockage, urine flow slows down but does not halt completely. This condition may not result in any obvious signs and symptoms. A complete blockage of ureter (for example, due to a kidney stone) halts the flow of urine completely. The complete obstruction may happen abruptly, causing appearance of symptoms within a few minutes.

Hydronephrosis or hydroureter may result from significant partial or complete obstruction of the ureters. Hydronephrosis refers to accumulation of fluid within the kidneys as the urinary flow through the ureters get obstructed. Hydroureter refers to a dilation of the ureter due to accumulation of urine in it.

Signs and Symptoms

Not all cases of blocked ureters give rise to obvious signs and symptoms. In case of unilateral partial blockage, the unaffected ureter compensates for the slow urinary flow through the blocked ureter. When signs and symptoms do appear, their severity varies with the extent of the blockage.

The following are some of the common signs and symptoms associated with blocked ureters:

  • Reduction in urine output occurs in case of partial or unilateral blockage. The reduced urine output is medically referred to as oliguria.
  • Abdominal pain may occur in the region where the kidneys are located (lateral flanks of the abdominal wall).
  • Blood may also be seen in the urine. This condition is medically referred to as hematuria.
  • Fever may occur, especially in case of kidney infection.
  • In case of bilateral obstruction of both ureters, swelling may be seen in the legs. Left untreated, the swelling may become generalized.

Read more on urinary problems.

Causes of Blocked Ureters

Obstruction to urinary flow through the ureters could occur due to a variety of causes. Broadly, the causes of blocked ureter can be classified into intrinsic and extrinsic factors. Intrinsic causes of blocked ureter exist within the ureter itself. On the other hand, extrinsic causes of blocked ureter exist outside the ureter, and typically involve the neighboring tissues.

Problems within the urinary system

The following are some of the intrinsic causes of blocked ureter:

  • Kidney stones: Kidney stones with less than 5mm diameter can find their way into the ureter and cause sudden blockage. However, large kidney stones cannot enter the ureter.
  • Blood clots: When blood in seen in the urine, a blocked ureter may be caused by blood clots. This is usually seen in cases of massive hematuria. The blood in the urine may be caused by tumors, kidney stones or papillary necrosis.
  • Ureteral strictures: Ureteral strictures refer to narrowing of the lumen of ureters. This could result from various causes. Some ureteral strictures are congenital, and can cause symptoms of blocked ureter in early childhood. Other causes could be acquired, usually through scarring caused by long term or recurrent inflammation of the ureters. Recurrent kidney stones and urinary tract infections (abbreviated as UTI) are examples of conditions that can lead to acquired ureteral strictures.
  • Tumors: Both benign and malignant tumors can occur within the ureters. Benign tumors within ureters are not very common. Blocked ureters are mainly caused by malignant tumors (especially transitional cell carcinomas).
  • Iatrogenic obstruction: Iatrogenic obstruction of ureters refer to obstructions resulting from complications of certain medical procedures such as kidney transplant, ureteroscopy, and radiation therapy.
  • Bladder outlet obstruction: Blockage of urine outflow from the bladder can cause bilateral blockage of the ureters.
  • Ureteropelvic junction obstruction: The exact cause of ureteropelvic junction obstruction is not known. It is a functional obstruction that may be congenital and can affect both the ureters. Normally, uretereopelvic junction obstruction does not cause significant problems until another intrinsic or extrinsic cause impacts the same site.

Problems outside of the urinary system

The following are some of the extrinsic causes of blocked ureter:

  • Tumors: Tumors (especially sarcomas and lymphomas) of ovaries, uterus, urinary bladder and prostate can cause blockage of the ureters.
  • Endometriosis: Chronic endometriosis can lead to formation of scar tissue around the ureter, leading to its blockage.
  • Pregnancy: The expansion of uterus during pregnancy can lead to compression and blockage of the ureters. Blockage in this condition could be bilateral.
  • Peri-ureteral inflammatory conditions: Inflammation of tissues around the ureters could also lead to blocked ureter. Examples of such inflammatory conditions include peritonitis, salpingitis, and diverticulitis.
  • Retroperitonial fibrosis: Retroperitoneal fibrosis refers to formation of fibrous tissue behind the peritoneum. It is not very common, but could lead to constriction and blockage of ureter. Retroperitoneal fibrosis may be caused by certain drugs, inflammation of abdominal organs and some types of cancers.
  • Constipation: In cases of severe constipation, distension of the bowels may cause constriction of the ureter. However, this occurs very rarely.

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