{{More medical citations needed|date=December 2018}} {{Infobox medical condition (new) | name = Bladder outlet obstruction | synonyms = BOO, bladder outlet blockage, infravesical urinary obstruction, obstructive uropathy | image = | alt = | caption = | pronounce = | field = | symptoms = | complications = | onset = | duration = | types = | causes = | risks = | diagnosis = | differential = | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }} '''Bladder outlet obstruction''' (or '''obstructive uropathy''') occurs when urine is unable to flow from the [[kidneys]] through the [[ureter]]s and out of the [[Urinary bladder|bladder]] through the [[urethra]]. Decreased flow of urine leads to swelling of the urinary tract, called [[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]] levels and [[Pulmonary hypoplasia|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 system|urinary tract]] 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]], there is no known cause.<ref name=":0" /> 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.<ref name=":0" /><ref name=":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.<ref name=":0" /><ref name=":2" /> UPJ obstruction is transient in most cases.<ref name=":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.<ref name=":0" />
==== Posterior urethral valves ==== [[Posterior urethral valve]]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.<ref name=":0" /> 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.<ref name=":0" />
==== Ureterocele ==== A [[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.<ref name=":0" />
==== 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 [[Medical ultrasound|prenatal ultrasonography]] as dilation of the fetal [[Urinary system|urinary tract]]<ref name=":1">{{cite book|title=Pediatric nephrology|last1=Avner|first1=Ellis|isbn=978-3-662-43595-3|edition= 7th|date=2016-04-08|publisher=Springer }}</ref> 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.<ref name=":1" />
==== 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]] 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.<ref>{{Cite web|url=https://www.uptodate.com/contents/prune-belly-syndrome?search=prune%20belly%20syndrome&source=search_result&selectedTitle=1~20&usage_type=default&display_rank=1|title=UpToDate|website=www.uptodate.com|access-date=2018-11-04}}</ref>
==== 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.<ref name=":0" />
==Terminology== Bladder neck obstruction is a condition where the [[bladder neck]] does not open enough during [[Urination|voiding]].<ref>{{cite journal|pmc=1477631 | pmid=16985885 | volume=7 | title=Primary bladder neck obstruction in men and women | year=2005 | journal=Rev Urol | pages=S12–7| last1=Nitti | first1=V. W. | issue=Suppl 8 }}</ref>
=== 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.<ref name=":0">{{cite book|title=Clinical pediatric nephrology|isbn=978-1-4822-1462-8|edition= 3rd|last1=Kher|first1=Kanwal K.|last2=William Schnaper|first2=H.|last3=Greenbaum|first3=Larry A.|year=2016|publisher=CRC Press }}</ref><ref name=":2">{{Cite book|title=Brenner & Rector's the kidney|others=Skorecki, Karl,, Chertow, Glenn M.,, Marsden, Philip A.,, Taal, Maarten W.,, Yu, Alan S. L.|isbn=9781455748365|edition= Tenth |location=Philadelphia, PA|oclc=921886335|date = 2015-10-28}}</ref>
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]] in an article published in 1999.<ref>{{cite news|title=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|last1=Pope IV|first1=J C|last2=Brock III |first2=J W|last3=Adams|first3=M C|last4=Stephens|first4=F D |last5=Ichikawa|first5=I |date=Sep 1999|publisher=Journal of American Society of Nephrology|pmid=10477156 }}</ref> Their preceding studies in both animals and humans supported by a grant from [[National Institutes of Health|NIH]] (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.<ref>{{cite journal|title=Role of the angiotensin type 2 receptor gene in congenital anomalies of the kidney and urinary tract, CAKUT, of mice and men|last1=Nishimura|first1=H|last2=Yerkes |first2=E|last3=Hohenfellner|first3=K|last4=Miyazaki|first4=Y |last5=Ma|first5=J|last6=Hunley|first6=T E |last7=Yoshida |first7=H |last8=Ichiki|first8=T |last9=Thredgill|first9=D |last10=Phillips III |first10=J A |last11=Hogan|first11=B M |last12=Fogo |first12=A|last13=Brock III|first13=J W |last14=Inagami|first14=T |last15=Ichikawa|first15=I |date=Jan 1999|volume=3 |issue=1 |pages=1–10 |journal=Molecular Cell|doi=10.1016/s1097-2765(00)80169-0 |pmid=10024874 }}</ref>
CAKUT can be classified by the degree and type of malformation as follows:
==== Aplasia ==== [[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 [[nephron]]s, or functional units of the kidney.<ref name=":2" />
==== Dysplasia ==== Malformation of kidney or bladder architecture.<ref name=":2" /> A dysplastic kidney is typically small for age and may contain cysts. A [[multicystic dysplastic kidney]] is an extreme example of renal dysplasia.{{citation needed|date=April 2021}}
==== Isolated collecting duct dilation ==== Dilation of the renal pelvis, ureters, or both. Also called [[hydronephrosis]].<ref name=":2" />
==== Anomalies of position ==== Kidneys and ureters located in incorrect position, including [[horseshoe kidney]] and ectopic ureters.<ref name=":2" />
== See also == * [[Overflow incontinence]]
== References == {{reflist}}
== External links == {{Medical resources | ICD10 = <!--{{ICD10|Xxx.x}}--> | ICD9 = <!--{{ICD9|xxx}}--> | ICDO = | OMIM = | DiseasesDB = | MedlinePlus = 002238 | eMedicineSubj = | eMedicineTopic = | MeSH = | GeneReviewsNBK = | GeneReviewsName = | Orphanet = }}
[[Category:Urinary bladder disorders]] [[Category:Kidney diseases]]