Posterior Urethral Valves Flashcards
What are posterior urethral valves (PUV)?
Congenital obstructive membranes in the male urethra, caused by abnormal insertion of the Wolffian ducts, leading to bladder outlet obstruction with a membranous barrier.
Why do posterior urethral valves occur exclusively in males?
Because they result from abnormal insertion of the Wolffian ducts, which are absent in females.
What is the primary pathophysiological consequence of posterior urethral valves?
Bladder outlet obstruction leading to bladder distension, bilateral hydronephrosis, and vesicoureteral reflux.
What are the key ultrasound findings of posterior urethral valves on antenatal screening?
Bilateral hydronephrosis, thickened and dilated bladder, oligohydramnios, and dilated proximal urethra.
Why does oligohydramnios occur in severe posterior urethral valves?
Obstruction prevents fetal urine output, reducing amniotic fluid volume and leading to Potter sequence.
How does posterior urethral valves present postnatally?
Poor urinary stream, recurrent UTIs, bladder distension, failure to thrive, and risk of chronic kidney disease.
What is Potter sequence and how is it related to posterior urethral valves?
A syndrome of pulmonary hypoplasia, flattened facies, and limb deformities due to severe oligohydramnios from fetal urinary obstruction.
How does ureteropelvic junction (UPJ) obstruction differ from posterior urethral valves?
UPJ obstruction causes unilateral hydronephrosis without bladder distension, whereas PUV causes bilateral hydronephrosis with a thickened bladder.
How does vesicoureteral reflux (VUR) differ from posterior urethral valves?
VUR leads to retrograde urine flow but does not cause bladder outlet obstruction or thickened bladder walls as seen in PUV.
How does a duplicated collecting system differ from posterior urethral valves?
Duplicated systems cause partial obstruction but do not lead to the thickened bladder wall and severe obstruction seen in PUV.
What is the immediate management for a newborn diagnosed with posterior urethral valves?
Bladder decompression with a Foley catheter to relieve obstruction.
What is the first-line diagnostic test for suspected posterior urethral valves?
Voiding cystourethrogram (VCUG) to assess urethral dilation and bladder dysfunction.
What is the classic finding on VCUG for posterior urethral valves?
Dilated posterior urethra with a linear defect during the voiding phase.
What additional imaging is useful for evaluating kidney function in posterior urethral valves?
Renal and bladder ultrasound to assess hydronephrosis and kidney damage.
What is the definitive treatment for posterior urethral valves?
Cystoscopic ablation of the posterior urethral valve.
Why do infants with PUV have a high risk for chronic kidney disease (CKD)?
Persistent bladder dysfunction and high urinary tract pressures can lead to progressive renal scarring and failure.
What are the long-term complications of posterior urethral valves?
Chronic kidney disease, recurrent UTIs, bladder dysfunction, and vesicoureteral reflux.
Why do some infants with PUV develop vesicoureteral reflux (VUR)?
High intravesical pressures force urine back into the ureters, predisposing to infection and kidney damage.
How is bladder dysfunction managed post-posterior urethral valve ablation?
Bladder training, intermittent catheterization, and anticholinergic medications to reduce detrusor overactivity.
Why is posterior urethral valves the most common cause of severe obstructive uropathy in children?
Because it leads to significant bladder outlet obstruction, affecting the entire urinary tract.
What is the prognosis for infants with posterior urethral valves who undergo early treatment?
Better renal outcomes with early intervention, but risk of CKD remains due to prenatal kidney injury.
When should a kidney transplant be considered in posterior urethral valve patients?
In cases of end-stage renal disease due to progressive CKD despite treatment.
