# Bladder outlet obstruction

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Medical condition

Bladder outlet obstruction Other names BOO, bladder outlet blockage, infravesical urinary obstruction, obstructive uropathy

**Bladder outlet obstruction** (or **obstructive uropathy**) occurs when urine is unable to flow from the [kidneys](/source/Kidneys) through the [ureters](/source/Ureter) and out of the [bladder](/source/Urinary_bladder) through the [urethra](/source/Urethra). Decreased flow of urine leads to swelling of the urinary tract, called [hydronephrosis](/source/Hydronephrosis). 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](/source/Amniotic_fluid) levels and [incomplete lung maturation](/source/Pulmonary_hypoplasia). 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](/source/Urinary_system) 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 [hydronephrosis](/source/Hydronephrosis), there is no known cause.[1] 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.[1][2] 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.[1][2] UPJ obstruction is transient in most cases.[2]

### 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.[1]

#### Posterior urethral valves

[Posterior urethral valves](/source/Posterior_urethral_valve) (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.[1] 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.[1]

#### Ureterocele

A [ureterocele](/source/Ureterocele) 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.[1]

#### 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](/source/Medical_ultrasound) as dilation of the fetal [urinary tract](/source/Urinary_system)[3] 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.[3]

#### 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](/source/VACTERL_association) is a constellation of congenital anomalies including vertebral, anal, cardiac, tracheoesophageal, renal and limb defects. [Prune belly syndrome](/source/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.[4]

#### 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.[1]

## Terminology

Bladder neck obstruction is a condition where the [bladder neck](/source/Bladder_neck) does not open enough during [voiding](/source/Urination).[5]

### 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](/source/Chronic_kidney_disease) and end-stage renal disease in children.[1][2]

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](/source/Vanderbilt_Children's_Hospital) in an article published in 1999.[6] Their preceding studies in both animals and humans supported by a grant from [NIH](/source/National_Institutes_of_Health) (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.[7]

CAKUT can be classified by the degree and type of malformation as follows:

#### Aplasia

[Aplasia](/source/Aplasia) 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 [nephrons](/source/Nephron), or functional units of the kidney.[2]

#### Dysplasia

Malformation of kidney or bladder architecture.[2] A dysplastic kidney is typically small for age and may contain cysts. A [multicystic dysplastic kidney](/source/Multicystic_dysplastic_kidney) is an extreme example of renal dysplasia.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

#### Isolated collecting duct dilation

Dilation of the renal pelvis, ureters, or both. Also called [hydronephrosis](/source/Hydronephrosis).[2]

#### Anomalies of position

Kidneys and ureters located in incorrect position, including [horseshoe kidney](/source/Horseshoe_kidney) and ectopic ureters.[2]

## See also

- [Overflow incontinence](/source/Overflow_incontinence)

## References

1. ^ [***a***](#cite_ref-:0_1-0) [***b***](#cite_ref-:0_1-1) [***c***](#cite_ref-:0_1-2) [***d***](#cite_ref-:0_1-3) [***e***](#cite_ref-:0_1-4) [***f***](#cite_ref-:0_1-5) [***g***](#cite_ref-:0_1-6) [***h***](#cite_ref-:0_1-7) [***i***](#cite_ref-:0_1-8) Kher, Kanwal K.; William Schnaper, H.; Greenbaum, Larry A. (2016). *Clinical pediatric nephrology* (3rd ed.). CRC Press. [ISBN](/source/ISBN_(identifier)) [978-1-4822-1462-8](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4822-1462-8).

1. ^ [***a***](#cite_ref-:2_2-0) [***b***](#cite_ref-:2_2-1) [***c***](#cite_ref-:2_2-2) [***d***](#cite_ref-:2_2-3) [***e***](#cite_ref-:2_2-4) [***f***](#cite_ref-:2_2-5) [***g***](#cite_ref-:2_2-6) [***h***](#cite_ref-:2_2-7) *Brenner & Rector's the kidney*. Skorecki, Karl,, Chertow, Glenn M.,, Marsden, Philip A.,, Taal, Maarten W.,, Yu, Alan S. L. (Tenth ed.). Philadelphia, PA. 2015-10-28. [ISBN](/source/ISBN_(identifier)) [9781455748365](https://en.wikipedia.org/wiki/Special:BookSources/9781455748365). [OCLC](/source/OCLC_(identifier)) [921886335](https://search.worldcat.org/oclc/921886335).{{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: CS1 maint: location missing publisher ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_location_missing_publisher)) CS1 maint: others ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_others))

1. ^ [***a***](#cite_ref-:1_3-0) [***b***](#cite_ref-:1_3-1) Avner, Ellis (2016-04-08). *Pediatric nephrology* (7th ed.). Springer. [ISBN](/source/ISBN_(identifier)) [978-3-662-43595-3](https://en.wikipedia.org/wiki/Special:BookSources/978-3-662-43595-3).

1. **[^](#cite_ref-4)** ["UpToDate"](https://www.uptodate.com/contents/prune-belly-syndrome?search=prune%20belly%20syndrome&source=search_result&selectedTitle=1~20&usage_type=default&display_rank=1). *www.uptodate.com*. Retrieved 2018-11-04.

1. **[^](#cite_ref-5)** Nitti, V. W. (2005). ["Primary bladder neck obstruction in men and women"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1477631). *Rev Urol*. **7** (Suppl 8): S12–7. [PMC](/source/PMC_(identifier)) [1477631](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1477631). [PMID](/source/PMID_(identifier)) [16985885](https://pubmed.ncbi.nlm.nih.gov/16985885).

1. **[^](#cite_ref-6)** Pope IV, J C; Brock III, J W; Adams, M C; Stephens, F D; Ichikawa, I (Sep 1999). "How they begin and how they end: classic and new theories for the development and deterioration of congenital anomalies of the kidney and urinary tract, CAKUT". Journal of American Society of Nephrology. [PMID](/source/PMID_(identifier)) [10477156](https://pubmed.ncbi.nlm.nih.gov/10477156).

1. **[^](#cite_ref-7)** Nishimura, H; Yerkes, E; Hohenfellner, K; Miyazaki, Y; Ma, J; Hunley, T E; Yoshida, H; Ichiki, T; Thredgill, D; Phillips III, J A; Hogan, B M; Fogo, A; Brock III, J W; Inagami, T; Ichikawa, I (Jan 1999). "Role of the angiotensin type 2 receptor gene in congenital anomalies of the kidney and urinary tract, CAKUT, of mice and men". *Molecular Cell*. **3** (1): 1–10. [doi](/source/Doi_(identifier)):[10.1016/s1097-2765(00)80169-0](https://doi.org/10.1016%2Fs1097-2765%2800%2980169-0). [PMID](/source/PMID_(identifier)) [10024874](https://pubmed.ncbi.nlm.nih.gov/10024874).

## External links

Classification D External resources MedlinePlus: 002238

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Adapted from the Wikipedia article [Bladder outlet obstruction](https://en.wikipedia.org/wiki/Bladder_outlet_obstruction) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Bladder_outlet_obstruction?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.