Congenital Anomalies of the Urinary Tract

Forfar & Arneil 7th Edition · Renal agenesis · Renal ectopia/fusion (horseshoe) · Duplex systems · Renal dysplasia/hypoplasia · Multicystic dysplastic kidney · Posterior urethral valves · PUJ & VUJ obstruction · Vesicoureteric reflux (VUR)
📌 Key principles: Congenital urinary tract anomalies are common (~1 in 500). Bilateral renal agenesis is fatal (Potter sequence). Posterior urethral valves (PUV) cause bladder outlet obstruction in males. VUR predisposes to UTI and renal scarring. Multicystic dysplastic kidney (MCDK) usually involutes spontaneously.

📖 Congenital Urinary Tract Anomalies: Core Concepts

🧬 Renal agenesis & fusion
Unilateral renal agenesis (1:1000) – contralateral hypertrophy. Bilateral agenesis (Potter sequence) – fatal. Horseshoe kidney (1:400) – fusion at lower poles, risk of obstruction, stones.
🔄 Duplex systems & dysplasia
Duplex kidney (1:125) – complete or incomplete. Upper moiety: ureterocele, obstruction; lower moiety: reflux. Multicystic dysplastic kidney (MCDK) – non-functioning, involutes.
🚰 Posterior urethral valves (PUV)
Only in males. Bladder outlet obstruction → bilateral hydronephrosis, trabeculated bladder, renal dysplasia. Presents with poor stream, UTI, renal failure. MCUG diagnostic.
⛔ Pelviureteric (PUJ) & vesicoureteric (VUJ) obstruction
PUJ obstruction: most common cause of hydronephrosis in utero. VUJ obstruction: megaureter. Surgery if significant obstruction or symptoms.
🔄 Vesicoureteric reflux (VUR)
Retrograde urine flow from bladder. Grades I-V. Primary (immature ureteric orifice) or secondary (PUV, neurogenic bladder). Risk of UTI and renal scarring. Prophylaxis for high grade.
📊 Key imaging: Antenatal ultrasound (detects hydronephrosis). Postnatal ultrasound, MCUG (micturating cystourethrogram) for VUR and PUV, DMSA for scarring, MAG3 for obstruction.

🔍 Clinical approach to congenital urinary tract anomalies

1
Antenatal diagnosis – hydronephrosis – Most common finding. Measure renal pelvis AP diameter: <4mm normal at 20w. Postnatal ultrasound at 48h-7d (avoid first 48h).
2
Postnatal evaluation of hydronephrosis – Ultrasound: severity, parenchymal thickness, ureter, bladder. MCUG to exclude VUR or PUV. MAG3 renogram for obstruction (PUJ).
3
Posterior urethral valves – presentation – Male neonate: poor urinary stream, palpable bladder, bilateral hydronephrosis, renal failure. MCUG shows elongated posterior urethra, trabeculated bladder.
4
VUR – grading and management – Grade I (ureter only), II (renal pelvis, no dilatation), III (mild dilatation), IV (moderate dilatation, blunted calyces), V (severe dilatation, tortuous ureter).
5
Multicystic dysplastic kidney (MCDK) – Unilateral, non-functioning, multiple cysts. Ultrasound shows cysts of varying size, no parenchyma. Follow with ultrasound until involution. Contralateral kidney hypertrophy.
6
PUJ obstruction – Ultrasound: hydronephrosis with dilated renal pelvis, normal ureter. MAG3 shows delayed drainage. Pyeloplasty if symptoms or decreased function.
📌 Clinical pearl: In a male newborn with poor urinary stream and a palpable bladder, suspect posterior urethral valves. Do not catheterise – perform urgent MCUG. Associated with renal dysplasia.

📋 Stepwise management of congenital anomalies

1
Posterior urethral valves – management – Primary: catheter drainage, correct electrolytes. Endoscopic valve ablation (cystoscopy). Monitor for renal failure, bladder dysfunction. Manage hypertension.
2
VUR – medical management – Antibiotic prophylaxis (trimethoprim, nitrofurantoin) for grade III-V. Treat UTI promptly. Surgical reimplantation for breakthrough infections, high grade with scarring, non-compliance.
3
PUJ obstruction – indications for surgery – Symptomatic (pain, stones, UTI), reduced split renal function (<40%), or progressive loss. Pyeloplasty (Anderson-Hynes).
4
MCDK – follow-up – Ultrasound at 3,6,12 months, then annually until involution or age 5. Monitor blood pressure. Rarely nephrectomy if large, hypertension, or persistent symptoms.
5
Duplex kidney with ureterocele – Endoscopic incision of ureterocele. Upper pole nephrectomy or ureteroureterostomy if non-functioning moiety.
6
Horseshoe kidney – complications
Risk of PUJ obstruction, stones, infection, Wilms tumour (slightly increased). Monitor annually.
⚠️ VUR grading (International Reflux Study): Grade I: ureter only; II: pelvis, no calyceal dilatation; III: mild/moderate dilatation; IV: moderate dilatation, blunted calyces; V: severe dilatation, tortuous ureter.

🧠 Reflex prompts: congenital urinary anomalies

👶 A newborn male with poor urinary stream, palpable bladder, bilateral hydronephrosis. Next step?
Suspected posterior urethral valves. Do NOT catheterise. Urgent MCUG for diagnosis. Assess renal function, electrolytes.
🩻 Antenatal ultrasound shows right multicystic kidney, normal left kidney. Postnatal management?
Ultrasound after 48h to confirm MCDK. No intervention, serial ultrasounds until involution. Monitor BP. Contralateral hypertrophy expected.
🚰 A child with recurrent UTIs, ultrasound shows left hydronephrosis, normal ureter. Most likely diagnosis?
Pelviureteric junction (PUJ) obstruction. MAG3 renogram to assess drainage and split function. Pyeloplasty if symptomatic.
🔄 A 3-year-old girl with febrile UTI, MCUG shows grade IV VUR. Management?
Antibiotic prophylaxis (trimethoprim). Consider surgical reimplantation if breakthrough infections, poor compliance, or new scarring.
🧬 A child with antenatal hydronephrosis, postnatal ultrasound shows moderate hydronephrosis, normal ureter, normal bladder. Next investigation?
MCUG to exclude VUR, MAG3 renogram to assess PUJ obstruction if significant hydronephrosis persists.
🩺 A 6-year-old boy with hypertension, proteinuria, unilateral small kidney. Ultrasound shows global scarring. Likely cause?
Reflux nephropathy (previous VUR with scarring). DMSA scan shows scarring. Manage BP with ACE inhibitor.
🩻 What is the most common cause of antenatal hydronephrosis?
Transient/physiological hydronephrosis (63%). Pathological: PUJ obstruction (11%), VUR (9%), megaureter (4%), PUV (1%).
🚻 A female child with duplex kidney, upper pole obstruction, and ureterocele. Treatment?
Endoscopic incision of ureterocele. Upper pole heminephrectomy if non-functioning and causing symptoms.
🔍 What is the incidence of horseshoe kidney?
1 in 400 births. Fusion of lower poles. Increased risk of PUJ obstruction, stones, Wilms tumour.
🩸 A newborn with bilateral renal agenesis. What is the typical presentation?
Potter sequence: oligohydramnios, pulmonary hypoplasia, characteristic facies (low-set ears, flattened nose), limb contractures. Fatal.