The ureters are the long narrow tubes that carry urine from each kidney to the bladder. Although this part of the urinary tract is often not given much consideration in diseases of the urinary system, the ureters can be affected by a number of conditions that will impact on the functioning of the kidney and could even lead to death. The ureters are muscular tubes approximately 30 centimeters long. It exits the kidney at the hilum, comes into close contact with common iliac arteries from the aorta. The ureters pass on the lateral abdominal wall and then enters the pelvis where it joins the urinary bladder, passing a short distance into it.

Although the luminal diameter is fairly constant throughout the course of the ureter, there are three areas of relative constriction – where the ureter communicates with the renal pelvis, where the ureter crosses the inlet of the pelvic brim and where the ureter penetrates the urinary bladder. These three sites are important points to consider in obstruction as particles, specifically kidney stones that pass out into the ureter, may become lodged thereby partially or completely blocking the ureter.

Partial and Complete Obstruction

Most blockages usually only affect one ureter (unilateral) and are partial thereby allowing kidney function to continue fairly unaffected. Very few diseases may afflict both ureters simultaneously and if this does occur, it can have grave consequences. As with most diseases affecting most hollow organs, an obstruction is usually expected to occur gradually. However the most common cause of ureteral obstruction – urinary stones – is of abrupt onset. Therefore there may be a complete obstruction which can cause the sudden onset of symptoms often within minutes.

A partial blockage of one ureter may be barely noticeable as the urine may still pass through, albeit with slowly, and the other kidney with an intact ureter will compensate for the urinary output. With significant partial ureteral obstruction or complete obstruction on one side, there may be hydronephrosis and/or hydroureter. A hydronephrosis is when the the pelvis of the kidney and eventually even the calyx becomes dilated as the fluid accumulates within it. Hydroureter is a dilation of the ureter as the urine accumulates within it and causes distension. A hydroureter is unlikely to occur with a blockage at the ureteropelvic junction – this is where the kidney (renal pelvis) and ureter meet.

Signs and Symptoms

The clinical features may vary to some degree depending on the cause of the ureteral obstruction. Some of the common signs and symptoms include :

  • Abdominal pain typically to the sides (flanks) as described under kidney pain location.
  • Oliguria – reduced urine output
  • Hematuria – blood in the urine
  • Fever as an infection particularly of the kidney may arise
  • Swelling of the legs if the obstruction is bilateral which may be followed by generalized swelling in severe untreated cases.

Causes of Ureteral Obstruction

The causes of a ureteral obstruction may be intrinsic or extrinsic. Intrinsic factors are those that occur within the ureter whereas extrinsic factors are outside of the ureter usually involving neighboring organs or structures.

Inside the Ureter

  • Kidney stones. Large kidney stones cannot enter the ureter but a stone less than 5mm in diameter can cause a sudden obstruction.
  • Blood clots may obstruct the ureter and this is usually seen with massive hematuria (blood in the urine). Bleeding in these cases may be due to tumors, papillary necrosis or kidney stones.
  • Tumors within the ureter may be benign or malignant. Benign tumors and fibroepithelial polyps are uncommon. Malignant tumors, specifically transitional cell carcinomas, may cause an obstruction within the ureter.
  • Ureteral strictures are narrowing of the ureters which may occur for various reasons. Congenital strictures are not uncommon and tend to cause symptoms from early in life. Acquired strictures are usually a result of scarring following recurrent or long term inflammation of the ureter as is seen with repeated kidney stones or urinary tract infections.
  • Iatrogenic obstruction are strictures that occur as a complication of a diagnostic or therapeutic procedures like ureteroscopy, kidney transplant or radiation therapy to the area.
  • Ureteropelvic junction obstruction is a functional obstruction and the exact cause is unclear. It may be congenital and can affect both sides (bilateral). It often does not create any significant problem unless some other intrinsic or extrinsic factor impacts at the site even to a slight degree.
  • Bladder outlet obstruction which prevents urine from existing the bladder and causes it to backup into the ureters in severe cases. This is likely to cause bilateral obstruction – affects both ureters.

Outside the Ureter

  • Periureteral inflammatory conditions is where there is inflammation of organs or structures lying around the the ureters. This may include conditions like peritonitis, diverticulitis and salpingitis (fallopian tube).
  • Retroperitoneal fibrosis is an uncommon type of periureteral inflammation and may be due to certain types of drugs, inflammatory conditions of abdominal organs which may not be in direct contact with the ureter or some types of cancers. Most cases are due to unknown causes. The formation of fibrous tissue behind the peritoneum may constrict the ureter.
  • Tumors of the ovaries, uterus, prostate or bladder, particularly lymphomas or sarcomas.
  • Endometriosis can sometimes affect the ureters and due to the chronic nature of this condition, it tends to lead to the development of scar tissue around the ureter.
  • Pregnancy where the enlarged pregnant uterus presses against the ureter at the pelvic brim thereby causing compression. This can affect both ureters simultaneously (bilateral).
  • Constipation may cause the distended bowel to press against the ureter. Overall this is uncommon and only seen in severe constipation.

Article reviewed by Dr. Greg. Last updated on December 4, 2011