Upper Tract Obstruction

Upper urinary tract obstruction is a common urological condition in which part of the ureter -- the tube that connects the kidney to the bladder -- becomes blocked and prevents the flow of urine. As a result, urine may back up into one or both kidneys, causing the bean-shaped organ(s) to swell (hydronephrosis). If not treated, permanent kidney damage can occur.

Causes of Upper Tract Obstruction

Upper urinary tract obstruction can happen suddently (acute), or it could be a long-term (chronic) issue. The most frequent causes vary by age. Children, young adults, and seniors tend to have different causes of obstruction that break down as follows:


In childhood, the condition is primarily caused by congenital (inherited) malformations of the urinary tract. Genetic conditions that result in upper urinary tract obstruction in children include:

  • Ureteropelvic junction abnormalities: The ureteropelvic junction is the interchange between the ureter and renal pelvis (the part of the ureter that connects to the kidney), and an abnormality here can limit or prevent the flow of urine from the kidney to the bladder.

  • Aberrant renal artery: If an additional (or "accessory") artery is attached to or located near the ureter, its proximity can block urine flow to the bladder.

  • Duplicated or duplex collecting system: A normal urinary tract system has two kidneys, each with one ureter connected to it. In a duplicated collecting system (also called a duplex system), one or both kidneys have two ureters attached, and -- while these duplex kidneys often function perfectly well -- sometimes the second ureter can interfere with kidney or bladder function.

  • Ectopic ureter: When a ureter terminates somewhere other than the bladder (e.g., the urethra or the vagina), it's referred to as an ectopic ureter and typically results in urine backflow.

  • Ureterocele: A ureterocele occurs when the portion of the ureter closest to the bladder expands and forms a balloon-like sac. This sac can collect urine, preventing it from flowing into the bladder, and even force it back up into the kidney.

  • Ureterovesical junction abnormalities: The ureterovesical junction is where ureter and bladder join together. Malformations of this junction can cause urine to either collect there or reflux back into the kidney.

Young Adults

In young adults, the principle cause of upper urinary tract obstruction is kidney stones or calculi. Kidney stones develop when minerals in the blood become concentrated and settle out of the urine in crystalline structures. Over time, the crystals grow harder and larger, blocking urine flow. The following are less-common but additional causes of upper urinary tract obstruction in young adults:

  • Narrowing of the ureter due to surgery: Surgical procedures performed on the ureter may cause scar tissue to develop, which can narrow the ureter and potentially lead to an obstruction.

  • Fibroids: These benign tissue masses form in a woman's uterus. If fibroids become large enough, they can place pressure on the ureter and block urine flow.

  • Neoplasms: These tumors are masses of tissue that can be either benign or malignant. If present in the urinary system, neoplasms can block the flow of urine. When they occur in the female reproductive system (such as the uterus), they may place pressure on the ureter and cause it to collapse.

  • Blood clots: Clots that develop in the urinary system may migrate to the ureter, blocking urine flow.


The risk of developing upper tract obstruction is relatively low until the individual reaches the age of 60. At this age, upper tract obstruction becomes more frequent, with the most common causes being:

  • Urinary tract tumors: Tumors are abnormal growths that can be either solid or fluid-filled. If one or more tumors develop along the urinary tract (kidneys, ureters, urethra and bladder), an obstruction can occur. When urine has no way to get out or has little room to filter through the urinary system, it builds up in areas along the urinary system, which can damage or scar the organ bearing the pressure of urine.

  • Enlarged prostate (benign prostatic hyperplasia): Benign prostatic hyperplasia is a common urological condition in men. The prostate is a walnut-sized gland that is located by the neck of the bladder, surrounding the urethra. As the prostate enlarges, it places pressure on the urethra, causing it to narrow and, in some cases, close completely. When urine becomes trapped or is unable to flow freely, it can accumulate or back up into the urinary tract system.

  • Cancer that has metastasized from other areas of the body: Cancer that metastasized from other parts of the body may directly invade organs of the urinary system or the female reproductive system. The pressure the tumors place on the ureters may obstruct the flow of urine.

  • Colon, cervical or uterine cancer: Pressure from tumors in the colon or uterus may impact the ureters, causing them to fold inward.

  • Kidney stones: Kidney stones that migrate to the ureter may block the flow of urine from the kidneys to the bladder, resulting in an upper tract obstruction.

Upper Tract Obstruction Symptoms

Symptoms of an upper urinary tract obstruction depend on how quickly the condition develops and its impact on the kidney. If it occurs slowly and only affects one kidney, there may be no discernible symptoms. If, however, it occurs suddenly and impacts both kidneys, symptoms may include:

Diagnosis of Upper Tract Obstruction

Patients who experience symptoms of upper urinary tract obstruction are typically evaluated using blood and urine tests that assess kidney function. If these yield abnormal results, additional tests can identify the underlying cause. Upper urinary tract obstruction is typically confirmed through imaging studies, which allow a doctor to visualize organs of the urinary tract. Imaging methods include:

Additionally, bladder catheterization in combination with imaging tests can evaluate organ function. Cystourethroscopy and voiding cystourethroscopy are two more non-invasive tests that take about an hour and allow a doctor to visualize urinary system function.

Treatment for Upper Tract Obstruction

Treatment for upper tract obstruction depends on the cause of the blockage. Those patients who have congenital abnormalities will require surgery, while those who have kidney stones may be able to pass the stones with time. Extrinsic conditions that result in upper urinary tract obstruction require treatment: For instance, an enlarged prostate may require surgery to remove all or part of the prostate in order to alleviate the obstruction.


Obstructive uropathy (urinary tract obstruction). (2012). The Merck Manual.

Zeidel ML. (2011). Obstructive uropathy. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; chap 125.

Singh I, Strandhoy JW, & Assimos DG. (2011). Pathophysiology of urinary tract obstruction. In: Wein AJ, ed. Campbell-WalshUrology. 10th ed. Philadelphia, Pa: Saunders Elsevier; chap 40.

Jorres, A., Ronco, C., & Kellum, J.A. (2010). Management of acute kidney problems. New York: Springer.

Obstructive uropathy. (2012). A.D.A.M. Medical Encyclopedia.

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