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

kidneys In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retro ...

through the

ureter The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In an adult human, the ureters typically measure 20 to 30 centimeters in length and about 3 to 4 millimeters in diameter. They are lin ...

s and out of the

bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distens ...

through the

urethra The urethra (: urethras or urethrae) is the tube that connects the urinary bladder to the urinary meatus, through which Placentalia, placental mammals Urination, urinate and Ejaculation, ejaculate. The external urethral sphincter is a striated ...

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

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

. 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 The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...

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 human 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 pressu ...

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 valve Posterior urethral valve (PUV) disorder is an obstructive developmental anomaly in the urethra and genitourinary system of male newborns. A posterior urethral valve is an obstructing membrane in the posterior male urethra as a result of abnormal ...

s (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 Prune belly syndrome (PBS) is a rare, genetic birth defect affecting about 1 in 40,000 births. About 97% of those affected are male. Prune belly syndrome is a congenital disorder of the urinary system, characterized by a triad of symptoms. The synd ...

(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 bladder () is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distensi ...

does not open enough during

voiding Urination is the release of urine from the bladder through the urethra in placental mammals, or through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, ures ...

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 Chronic kidney disease (CKD) is a type of long-term kidney disease, defined by the sustained presence of abnormal kidney function and/or abnormal kidney structure. To meet criteria for CKD, the abnormalities must be present for at least three mo ...

and end-stage renal disease in children. The term, Congenital Anomalies of the Kidney and Urinary Tract (CAKUT), was coined under the collaboration of pediatric nephrologists (child kidney disease experts) and pediatric urologists (child urinary tract experts) of the Laboratory of

Vanderbilt Children's Hospital Monroe Carell Jr. Children's Hospital at Vanderbilt, also known as Children's Hospital at Vanderbilt, is a nationally ranked pediatric acute care children's teaching hospital and entity of Vanderbilt University Medical Center in Nashville, Tenne ...

in an article published in 1999. Their preceding studies in both animals and humans supported by a grant from

NIH The National Institutes of Health (NIH) is the primary agency of the United States government responsible for biomedical and public health research. It was founded in 1887 and is part of the United States Department of Health and Human Service ...

(the Center of Excellence in Pediatric Nephrology and Urology, Ichikawa as the Principal Investigator) show that anomalies of the kidney, and the other parts of urinary tract in newborns are always found concurrently due to mechanisms shared by these organs during their embryonic development. 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 produ ...

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 structu ...

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 disorde ...

and ectopic ureters.

References

External links

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