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Posterior Urethral Valve (PUV) - Coggle Diagram
Posterior Urethral Valve (PUV)
Incidence
Main cause of bladder outflow obstruction in male infants.
Most common obstructive uropathy leading to chronic renal failure in childhood.
Incidence estimated at 1 in 5000 - 8000 male births (may be underestimated due to fetal and perinatal demise).
Anatomical Classification
Three types of PUV:
Type I (95%): Obstructing membrane radiating distally and anteriorly from the verumontanum toward the membranous urethra, fusing in the midline.
Type II: Prominent longitudinal folds of hypertrophied smooth muscle radiating cranially from the verumontanum to the posterolateral bladder neck (nonobstructive and clinically insignificant).
Type III: Membranous diaphragm with a central opening at the verumontanum.
Pathophysiology
Urethra:
The prostatic urethra above the PUV undergoes dilation and elongation.
Urinary Bladder:
Hyperplasia and hypertrophy of the detrusor muscle occur, resulting in a significantly thickened bladder wall.
Prenatal Ultrasound Findings:
"Megacystis" can be detected - a huge dilated bladder with a thickened wall.
Vesicoureteral Reflux (VUR) and VURD Syndrome:
Approximately 50% of patients with PUV show VUR at the time of diagnosis.
VUR can be attributed to two main factors:
High bladder pressure inducing incompetence of the uretero-vesical junction.
Congenital embryological lateral placement of the ureteral bud.
VURD Syndrome (Posterior Urethral
V
alves,
U
nilateral
R
eflux,
D
ysplasia):
Occurs in 15%-20% of PUV patients.
Characterized by unilateral VUR associated with unilateral significant renal damage or dysplasia.
This unilateral VUR with associated dysplasia acts as a "pop-off" mechanism, relieving pressure in the urinary system and protecting the contralateral kidney.
Urinary Ascites and Urinoma:
Increased pressure in the urinary tract may lead to the rupture of the caliceal fornix.
Urinary ascites can develop as a consequence.
Renal Failure:
mechanisms:
Congenital dysplasia, significantly reducing the amount of functioning renal parenchyma.
Urinary infections, which, in the presence of urinary dilatation and bladder dysfunction, can lead to further renal scarring.
Lung Development:
In the most severe cases of PUV, decreased urinary output due to renal dysplasia or severe hydronephrosis leads to oligohydramnios.
Oligohydramnios interferes with alveolar development, resulting in lung hypoplasia and perinatal death.
Antenatal diagnosis
About 10% of antenatally diagnosed obstructive uropathy is due to PUV.
Typical:bilateral hydroureteronephrosis, a distended bladder, and a dilated prostatic urethra, called a "keyhole" sign.
Oligohydraminos
Pulmonary hyperplasia
Clinical presentation
Neonates may present with delayed voiding, urine dribbling, reduced urinary stream, or respiratory distress due to pulmonary hypoplasia.
Other signs: abdominal mass, failure to thrive, lethargy, poor feeding, urosepsis, urinary ascites,
persistent diurnal incontinence,
or abdominal distention.
Physical examination
Urinary ascites can result in significant abdominal distention.
A palpable bladder secondary to the hypertrophic detrusor muscle is found.
Radiology
Renal and Bladder Ultrasonography:
Performed immediately postnatal, showing bilateral hydroureteronephrosis and a thick-walled, distended bladder.
Unfavorable signs: echogenic kidneys, subcortical cysts, and loss of corticomedullary differentiation.
Voiding Cystourethrogram (VCUG):
Gold standard for diagnosis, showing dilated posterior urethra, trabeculated bladder with cellules and diverticuli, and bladder neck hypertrophy.
Renal Nuclear Scintigraphy (99mTc-DMSA):
Accurate in assessing split renal function and the presence of renal scarring.
Treatment
Antenatal Treatment:
Creation of a vesico-amniotic shunt under sonographic guidance.
Complications may occur, including shunt malfunctioning and dislodgement, chorioamnionitis, damage to adjacent structures, or premature labor.
Neonatal Treatment:
Endoscopic Valve Ablation:
Aggressive treatment for electrolyte and fluid imbalance, sepsis, and acidosis.
Bladder drainage is crucial, achieved trans-urethral or through a suprapubic catheter.
Valve ablation with Bugbee or angled wire electrode, or a small-caliber laser fiber in 5, 7, & 12 o'clock
VCUG and renal US should be obtained 2-4 weeks after ablation to confirm satisfactory valve disruption and assess the upper urinary tracts and bladder emptying.
Transient Urinary Diversion (Cutaneous Vesicostomy):
Indicated in small or premature neonates when cystoscope size is an issue or severe hydroureteronephrosis urinary ascitis or high grade VUR is present.
May include vesicostomy, ureterostomy, or pelvicostomy.
Prognosis:
Unfavorable prognosis associated with:
Prenatal detection <24 weeks.
Hyperechoic kidneys, no evidence of pyramids.
Serum creatinine >0.8 mg/dl in the 1st year.
Bilateral VUR
Incontinence
Absence of pop-off mechanism