Urinary tract obstruction is a blockage that inhibits the flow of urine through its normal path (the urinary tract), including the kidneys, ureters, bladder, and urethra.
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A blockage (obstruction) anywhere along the urinary tract—from the kidneys, where urine is produced, to the urethra, through which urine leaves the body—can increase pressure inside the urinary tract and slow the flow of urine. An obstruction may occur suddenly or develop slowly over days, weeks, or even months. An obstruction may completely or only partially block part of the urinary tract. Sometimes only one kidney is affected, but obstruction may affect both kidneys.
The prevalence of urinary tract obstruction ranges from five in 10,000 to five in 1,000 depending on the cause. In children, obstruction is due mainly to birth defects affecting the urinary tract Overview of Kidney and Urinary Tract Birth Defects Birth defects are more common in the kidney and urinary system (urinary tract) than in any other system of the body. Defects can develop in the Kidneys (the two organs that filter waste from… read more . Men, particularly those older than 60, are also more likely to be affected because, as men age, the prostate gland tends to increase in size (a condition called benign prostatic hyperplasia Benign Prostatic Hyperplasia (BPH) Benign prostatic hyperplasia (BPH) is a noncancerous (benign) enlargement of the prostate gland that can make urination difficult. The prostate gland enlarges as men age. Men may have difficulty… read more ) and block the flow of urine.
In hydronephrosis, the kidney is distended because the flow of urine is obstructed. Urine backs up behind the obstruction and remains in the kidney’s small tubes and central collecting area (renal pelvis).
Normally, urine flows out of the kidneys at extremely low pressure. If the flow of urine is obstructed, urine backs up behind the point of blockage, eventually reaching the small tubes of the kidney and its collecting area (renal pelvis), swelling (distending) the kidney and increasing the pressure on its internal structures. Such kidney distention is called hydronephrosis. The elevated pressure due to the obstruction may ultimately damage the kidney and can result in loss of its function. When the flow of urine is obstructed, stones Stones in the Urinary Tract read more (calculi) are more likely to form. An infection may develop when the flow of urine is obstructed because bacteria that enter the urinary tract are not flushed out. If both kidneys are obstructed, kidney failure Kidney Failure read more may result.
Long-standing distention of the renal pelvis and ureter can also inhibit the rhythmic muscular contractions that normally move urine down the ureter from the kidney to the bladder (peristalsis). Scar tissue may then replace the normal muscular tissue in the walls of the ureter, resulting in permanent damage.
Partial and complete obstruction tend to cause similar problems, but most problems, and particularly kidney damage, are more severe when obstruction is complete.
Blockage may be partial or complete, affect one side or both sides, and develop rapidly (acutely) or slowly (chronically). The most common causes overall are
Because BPH is so common in older men, obstruction is more common among men. Other common causes of obstruction include strictures Urethral Stricture A urethral stricture is scarring that narrows the urethra. A urethral stricture may be Present from birth Develop after an infection or injury A urethral stricture most commonly results from… read more (narrowing caused by scar tissue) of the ureter or urethra that develop after radiation therapy, surgery, or procedures done on the urinary tract.
Hydronephrosis of both kidneys can occur during pregnancy as the enlarging uterus compresses the ureters. Hormonal changes during pregnancy may worsen the problem by reducing the muscular contractions that normally move urine down the ureters. This condition, commonly called hydronephrosis of pregnancy, usually resolves when the pregnancy ends, although the renal pelvis and ureters may remain somewhat distended afterward.
Symptoms depend on the cause, location, and duration of the obstruction. When the obstruction begins quickly and distends the bladder, ureter, and/or the kidney, it usually causes pain. If the kidney is distended, renal colic can develop. Renal colic is an excruciating pain between the ribs and hip on the affected side that comes and goes every few minutes. The pain may extend into a testis or the vaginal area. People may have nausea and vomiting.
Obstruction of one ureter does not reduce how much people urinate. Obstruction can stop or reduce urination if blockage affects the ureters from both kidneys or if it affects the urethra. Obstruction of the urethra or bladder outlet may cause pain, pressure, and distention of the bladder.
People who have slowly progressive obstruction that causes hydronephrosis may have no symptoms, or they may have attacks of dull, aching discomfort in the flank (the part of the back between the lower end of the ribs and the spine) on the affected side. Sometimes, a kidney stone temporarily blocks the ureter and causes pain that occurs intermittently.
Obstruction that leads to hydronephrosis may cause vague digestive tract symptoms, such as nausea, vomiting, and abdominal pain. These symptoms sometimes occur in children when hydronephrosis results from a birth defect in which the junction of the ureter and renal pelvis is too narrow (ureteropelvic junction obstruction).
People who have urinary tract infections Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria… read more (UTIs) may have pus or blood in the urine, fever, and discomfort in the area of the bladder or kidneys.
Early diagnosis is important, because most cases of obstruction can be corrected and because a delay in treatment can lead to irreversible kidney damage. Doctors may suspect obstruction because of a person’s symptoms, such as renal colic, symptoms of bladder distention, or a decrease in the volume of urine. A distended kidney can rarely be felt in the flank, usually if the kidney is greatly enlarged in an infant or a child or a thin adult. A distended bladder can sometimes be felt in the lower part of the abdomen just above the pubic bone.
Bladder catheterization (insertion of a hollow, soft tube through the urethra) is often the first diagnostic test done in people with symptoms that suggest the bladder is distended, such as pelvic pressure or distention. If the catheter drains a large amount of urine from the bladder, then either the bladder outlet or the urethra is obstructed. Many doctors do ultrasonography to determine whether the bladder is filled with a large amount of urine before doing bladder catheterization.
Imaging tests can be done to identify evidence of obstruction, such as hydronephrosis or a site of blockage, when the presence or site of obstruction is in doubt. For example, ultrasonography Ultrasonography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating… read more is a very useful test in most people (particularly children and pregnant women) because it is fairly accurate and does not expose the person to any radiation. However, ultrasonography is not always accurate in its ability to localize the site of obstruction.
Computed tomography Computed tomography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating… read more (CT) is an alternative. It is rapid and highly accurate, particularly at identifying stones. CT has traditionally involved exposure to significant doses of radiation. However, with newer CT scanners and new ways of using them, CT images can be obtained with much smaller doses of radiation. Magnetic resonance imaging Magnetic resonance imaging There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating… read more (MRI) is not as accurate as ultrasonography or CT, but MRI may be used if it is important to avoid exposing the person to radiation and if the site of obstruction cannot be seen with ultrasonography.
Other imaging tests, such as voiding cystourethrography Cystography and cystourethrography There are a variety of tests that can be used in the evaluation of a suspected kidney or urinary tract disorder. (See also Overview of the Urinary Tract.) X-rays are usually not helpful in evaluating… read more (VCUG), may be done to identify the site of obstruction, most often in children who have obstruction of the bladder or urethra. This imaging test can identify blockages in those structures (for example, caused by birth defects). It can also identify when urine flows backward from the bladder into the ureters (called vesicoureteral reflux) and causes urinary tract infections Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria… read more (UTIs) as well as obstruction. In VCUG, x-rays are taken after a radiopaque agent (dye) is inserted through a catheter inserted into the bladder.
Endoscopy with a special rigid or flexible endoscope (a cystoscope Cystoscopy A doctor can diagnose some disorders of the bladder and urethra (for example, bladder tumors, stones in the bladder, benign prostatic enlargement) by looking through a flexible viewing tube… read more ) can be used to examine the urethra, prostate, and bladder. A longer rigid or flexible endoscope (ureteroscope) can be passed into the ureters or kidneys to identify sites of obstruction. Sometimes the cystoscope, ureteroscope, or both can also be used to remove objects causing obstruction.
Blood tests Laboratory Tests for Blood Disorders Doctors select tests to help diagnose blood disorders based on the person”s symptoms and the results of the physical examination. Sometimes a blood disorder causes no symptoms but is discovered… read more and urine tests Urinalysis and Urine Culture Urinalysis, the testing of urine, may be necessary in the evaluation of kidney and urinary tract disorders and can also help evaluate bodywide disorders such as diabetes or liver problems. A… read more
are done. Blood test results are usually normal (particularly if obstruction is partial or acute), but tests may reveal high levels of blood urea nitrogen (sometimes called BUN), creatinine, or both if obstruction has completely blocked both kidneys for more than several hours. Results from an analysis of urine (urinalysis) are usually normal, but white blood cells and red blood cells may be present when a stone or a tumor is the cause of obstruction or when the obstruction is complicated by an infection.
Blockage can usually be relieved, but if relief takes too long, the kidney can be damaged permanently. However, because one normally functioning kidney is enough to sustain the body, permanent kidney failure is unlikely to develop unless both kidneys have been blocked for some time, usually at least a few weeks. The prognosis also depends on the cause of obstruction. For example, an untreated infection is more likely to cause kidney damage than a kidney stone Stones in the Urinary Tract read more .
Treatment usually aims to relieve the cause of obstruction. For example, if the urethra is blocked because of a benign enlarged or cancerous prostate, treatment can include drugs, such as hormonal therapy Hormonal therapy The risk of prostate cancer increases as men age. Symptoms, such as difficulty urinating, a need to urinate frequently and urgently, and blood in the urine, usually occur only after the cancer… read more
for prostate cancer, surgery, or enlargement of the urethra with dilators. Other treatments, such as lithotripsy or endoscopic surgery Stone removal Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Tiny stones may cause no symptoms, but larger stones… read more
, may be needed to remove stones that block the flow of urine in the ureter or kidney.
If the cause of obstruction cannot be rapidly corrected, particularly if there is infection, kidney failure, or severe pain, the urinary tract is drained. When acute hydronephrosis is caused by an obstruction that is not easily relieved, urine that has accumulated above the obstruction can be drained with a soft tube inserted through the back into the kidney (nephrostomy tube) or by insertion of a soft plastic tube that connects the bladder with the kidney (ureteral stent). Complications of nephrostomy tubes or ureteral stents can include displacement of the tube, infection, and discomfort. If the urethra is the site of an obstruction that must be relieved rapidly, doctors insert a soft rubber catheter into the bladder to drain urine.
Obstructions that cause chronic hydronephrosis usually do not require urgent relief. Complications of urinary tract obstruction, such as urinary tract infections Overview of Urinary Tract Infections (UTIs) In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria… read more and kidney failure Overview of Kidney Failure This chapter includes a new section on COVID-19 and acute kidney injury (AKI). Kidney failure is the inability of the kidneys to adequately filter metabolic waste products from the blood. Kidney… read more , if present, are treated promptly.