Bladder outlet obstruction (or obstructive uropathy) occurs when urine is unable to flow from the

kidneys The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

through the

ureter The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...

s and out of the

bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

through the

urethra The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra c ...

. Decreased flow of urine leads to swelling of the urinary tract, called

hydronephrosis Hydronephrosis describes hydrostatic dilation of the renal pelvis and calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the ureter, and hydronephroureter describes the dilation of t ...

. This process of decreased flow of urine through the urinary tract can begin as early as during intrauterine life and it prevents normal development of fetal kidneys and fetal urine. Low levels of fetal urine leads to low amniotic fluid levels and incomplete lung maturation. Older children and adults can also experience bladder outlet obstruction; however, this process is usually reversible and isn't associated with as many poor outcomes as in infants with congenital bladder outlet obstruction.

Causes

Bladder outlet obstruction is classified based on where along the

urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, c ...

the obstruction occurs, including upper urinary tract obstruction and lower urinary tract obstruction. Depending on the location of the obstruction, one or both sides of the urinary tract will be involved. In approximately 50% of cases of congenital

, there is no known cause. In many cases, obstruction along the urinary tract in utero leads to some form of CAKUT mentioned above.

Upper urinary tract obstruction

Upper urinary tract obstruction includes the renal pelvis and upper ureters.

Ureteropelvic junction obstruction

Ureteropelvic junction obstruction (UPJ obstruction) is an obstruction at the level of the ureter and renal pelvis. It is the most common cause of hydronephrosis detected in utero and is the most common anomaly detected on prenatal ultrasounds. It occurs in approximately 1 in every 1500 live births, is most commonly seen in males, involves the left ureter twice as often as the right ureter. UPJ obstruction is transient in most cases.

Lower urinary tract obstruction

Lower urinary tract obstruction involves the lower ureters, urinary bladder and the urethra.

Ureterovesicular junction obstruction

Ureterovesicular junction obstruction (UVJ obstruction) is an obstruction at the level of the ureter and bladder. It accounts for 20% of cases of hydronephrosis detected in utero. It is also most commonly seen in males and involved both sides of the urinary tract in approximately 25% of cases.

Posterior urethral valves

Posterior urethral valves (PUV) is an obstruction at the level of the urethra. It occurs in approximately 1 in every 5000 to 8000 live births and only occurs in males. Since PUV always affects both sides of the urinary tract, patients with posterior urethral valves are at the greatest risk for developing chronic kidney disease and end-stage renal disease due to obstructive uropathy.

Ureterocele

ureterocele A ureterocele is a congenital abnormality found in the ureter. In this condition the distal ureter balloons at its opening into the bladder, forming a sac-like pouch. It is most often associated with a duplicated collection system, where two uret ...

is a cystic dilation of the end of the ureter that can occur in the bladder and/or in the urethra. It occurs in approximately 1 in every 5000 live births, is most commonly seen in females and involves both ides of the urinary tract in approximately half of cases.

Urethral stenosis

Urethral stenosis is a narrowing of the urethra that prevents urine from exiting the bladder.

Diagnosis

Prenatal diagnosis

Bladder outlet obstruction can be identified during routine prenatal ultrasonography as dilation of the fetal

and decreased amniotic fluid levels. If dilation of the fetal urinary tract is suspected during pregnancy, an ultrasound of the infant's kidneys and bladder should be obtained after birth.

Postnatal diagnosis

If patients aren’t diagnosed with dilation of their urinary tract via ultrasound in utero, they can present after birth with vague symptoms such as abdominal pain, blood in their urine or a urinary tract infection.

Associated syndromes

If patients have other congenital anomalies, their bladder outlet obstruction may be recognized during evaluation for their related syndromes. For example,

VACTERL association The VACTERL association (also VATER association, and less accurately VACTERL syndrome) refers to a recognized group of birth defects which tend to co-occur (see below). This pattern is a recognized association, as opposed to a syndrome, because th ...

is a constellation of congenital anomalies including vertebral, anal, cardiac, tracheoesophageal, renal and limb defects. Prune belly syndrome (or Eagle-Barrett syndrome) is another group of congenital disorders that involves the kidneys and includes absent abdominal wall musculature, severe urinary tract abnormalities and bilateral undescended testicles.

Dietl crisis

Patients with an undiagnosed ureteropelvic junction obstruction may experience abdominal or flank pain after increased fluid intake, when their bladder is full or when they exercise.

Terminology

Bladder neck obstruction is a condition where the

bladder neck The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enter ...

does not open enough during

voiding Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)

Bladder outlet obstruction is included in the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). CAKUT is the most common cause of birth defects, occurring in 1 out of 1000 live births, and accounts for approximately half of all cases of chronic kidney disease and end-stage renal disease in children. CAKUT can be classified by the degree and type of malformation as follows:

Aplasia

Aplasia Aplasia (; from Greek ''a'', "not", "no" + ''plasis'', "formation") is a birth defect where an organ or tissue is wholly or largely absent. It is caused by a defect in a developmental process. Aplastic anemia is the failure of the body to produc ...

is a congenital absence of kidney tissue.

Simple hypoplasia

Kidneys that are small for age but still have normal renal architecture. This leads to a decrease in the number of

nephron The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ...

s, or functional units of the kidney.

Dysplasia

Malformation of kidney or bladder architecture. A dysplastic kidney is typically small for age and may contain cysts. A

multicystic dysplastic kidney Multicystic dysplastic kidney (MCDK) is a condition that results from the malformation of the kidney during fetal development. The kidney consists of irregular cysts of varying sizes. Multicystic dysplastic kidney is a common type of renal cyst ...

is an extreme example of renal dysplasia.

Isolated collecting duct dilation

Dilation of the renal pelvis, ureters, or both. Also called

Anomalies of position

Kidneys and ureters located in incorrect position, including

horseshoe kidney Horseshoe kidney, also known as ''ren arcuatus'' (in Latin), renal fusion or super kidney, is a congenital disorder affecting about 1 in 500 people that is more common in men, often asymptomatic, and usually diagnosed incidentally. In this disorder ...

and ectopic ureters.

References

External links

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