Urine Outflow Obstruction

Aetiology
Posterior urethral valves
- an abnormal congenital leaflets in the prostatic portion of the urethra that results in narrowing of the bladder outlet and obstruction of urine flow
- commonest cause of severe obstructive uropathy in children
- only affects male
- affects 1 in 5000-8000 live births
- inheritance is sporadic
Ureteropelvic junction obstruction
- results from fibrosis at the junction of the ureter & renal pelvis, which leads to obstructed urine flow
- increased pressure behind the obstruction results in proximal dilatation & hydronephrosis
- commonest cause of antenatally detected hydronephrosis
- lesions are commoner on the left, but 40% of cases are bilateral
- M>F
- Incidence of fetal hydronephrosis is nearly 1 in 500

Presentation
Posterior urethral valves
 - in neonates: may present with distended bladder, palpable kidney, abdominal distention, vomitting, poor urinary stream, failure to thrive, urinary tract infections, & renal insufficiency
 - in older: boys may present with voiding problems, poor urinary stream, urinary retention, bladder distension, hematuria, enuresis & hesitancy
Uteropelvic junction obstruction
 - palpable mass, nausea, vomitting, failure to thrive, abdominal pain, hypertension, renal tubular acidosis, signs & symptoms of a urinary tract infection, pyelonephritis, or sepsis
 - painful distention of the renal pelvis can cause unilateral flank pain with or without vomitting (Diettel crisis)

DDx
Meatal stenosis
midureteral valves
ureteral ectopia
ureterocele
Bladder neck obstruction
megaureter

Investigation
Diagnosis of a newborn with antenatal hydronephrosis includes: renal US within 48h if moderate to severe and at 7 days if mild
Posterior urethral valves
- are often diagnosed prior to birth with prenatal US: bilateral hydronephrosis, bladder wall thickening, widened prostatic urethra
- diagnosis of megacystic can be made as early as 10-14 weeks of gestation
- a voiding cystourethrogram may be used to define anatomy & demonstrate the posterior urethral valves
Uteropelvic junction obstruction
 - renal US to evaluate hydronephrosis during Diettal crisis
 - CT
 - dynamic renal scan to evaluate renal excretion & degree of obstruction
 - voiding cystourethogram (VCUG) to rule out reflux or posterior urethral valves; 10% of pt have contralateral low-grade vesicoureteral reflux

Management
Posterior urethral valves
- require placement of a transurethral catheter to relieve the obstruction
- correct electrolyte imbalance & infection, if persent
- if renal function is normal, corrective surgery with transurethral ablation of the valves is performed
- if uncontrollable infection, rising creatinine, or too small urethra are present, vesicostomy
Uteropelvic junction obstruction
 - observe, despite hydronephrosis. If no improvement in a few years, consider surgery
 - surgery if necessary if renal function worsens; it is usually well tolerated by neonates & young children
 - pyeloplasty is the surgery of choice
 - after release of obstruction (either via catheterisation or surgery), there is massive postobstructive diuresis (natriuresis & polyuria); as a result, "ins" & "outs" & electrolytes must be closely monitored & replaced

Prognosis
Posterior urethral valves
- may result in renal insufficiency or dysplasia
- creatinine nadir is best predictor of prognosis
- creatinine level >1 is more frequently associated with long-term renal insufficiency
Uteropelvic junction obstruction
 - increased risk of urinary stasis, infection, hamaturia, renal scarring secondary to obstruction
- may improve over time without treatment
- surgery is corrective