Posterior Urethral Valves
Lynn Salvador RDMS RDCS, Dr Alan Cameron 01 January 2001
Posterior urethral valves develop between the 4th and 6th week of fetal development when the primitive cloaca divides into the urinary and rectal compartments.
Type I valves are folds distal to the verumontanum deriving from the lateral wall of the urethra. It is believed that type I valves result from a more anterior insertion of the mesonephric ducts into the primitive cloaca than normal.
Type II valves are not obstructive as first described, but instead represent hypertrophy of the strip of superficial muscle that runs from the urethral orifice to the verumontanum.
Type III valves consist of a diaphragm-like structure with a small perforation and are located distal to the verumontanum but are not attached to it.
Approximately 95% of PUV are type I, with the majority of the remainder type III.
PUV results in incomplete emptying of the bladder with back pressure leading to dilation of the posterior urethra causing musculature hypertrophy of the bladder. In 70% of cases the ureters are dilated. Dysplasia of the kidneys may occur secondary to the obstruction, leading to renal failure and oligohydramnios with a concomitantly poor fetal prognosis.The diagnosis of PUV should be considered after 14 weeks if there is sonographic evidence of a lower urinary tract obstruction, including a dilated and hypertrophic bladder, hydroureter or hydronephrosis.
It is important to determine the sex of the baby because PUV is found almost exclusively in male fetuses, masculinised females and only rarely in normal females. The finding of ascites is indicative of bladder rupture. Some fetuses have presented with an elevated MSAFP.
Evidence of longstanding obstruction, usually associated with renal dysplasia and severe oligohydramnios, carries a poor prognosis; the finding of PUV later in pregnancy is associated with normal amniotic fluid volume which suggests a better prognosis.
In evaluating a fetus for management, a critical aspect is assessment of renal function. This has been attempted by furosemide stimulation of urine production, drainage of fetal bladder with documentation of reaccumulation of urine, and electrolyte determination in fetal urine.
Treatment has been attempted by insertion of a catheter into the bladder to drain urine into the amniotic cavity or by suprapubic vesicostomy.
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Dilated or "keyhole" configuration of the urethra
Male fetus (most commonly)
Bladder wall hypertrophy
Other obstructive uropathies such as ureteropelvic junction obstruction (UPJ), ureterovesical junction obstruction (UVJ), primary megaureter, massive vesicoureteral reflux and urethral stenosis, stricture or agenesis may also present in a similar manner.
Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a rapidly fatal triad characterised by a massively dilated, thick-walled bladder, normal to increased amniotic fluid, dilatation of the stomach with little peristaltic activity, bilateral hydronephrosis with no sign of renal damage, and hydroureter and is found primarily in females.
Multicystic, dysplastic kidneys are also associated with oligohydramnios, enlarged kidneys and ureters.
Distal obstructive uropathy-polydactyly
Prune belly urethral obstruction