Primary Obstructive Megaureter

Primary obstructive megaureter is a dilated ureter, usually defined as over 7 mm in diameter, with functional obstruction at the vesicoureteric junction and no vesicoureteric reflux or secondary cause.

It accounts for about 5 to 10% of antenatally detected urinary tract dilatation.

Boys are affected about 4 times more often than girls, the left side about twice as often as the right, and about 25% are bilateral. Most dilatation is non-progressive in infancy.

Pathophysiology. The distal ureter is aperistaltic from disordered muscle and excess collagen, so urine does not pass the junction well and the ureter proximal to it dilates. A true stricture is a less common cause.

Megaureter is classified as obstructed, refluxing, both refluxing and obstructed, or non-refluxing and non-obstructed. Secondary causes must be excluded, such as posterior urethral valves, neurogenic bladder, ureterocele and ectopic ureter.

Most are found on antenatal or infant ultrasound. Others present with febrile urinary infection, haematuria, flank pain, stones, and in adults with pain or incidental hydronephrosis. Poor feeding or failure to thrive in infants with infection. Large ureters can cause an abdominal mass.

• Ultrasound: ureteric diameter, renal pelvic diameter, parenchymal thickness and bladder wall. Repeat at 1 week to 1 month of age for antenatal dilatation.
• Voiding cystourethrogram to exclude reflux and valves.
• Diuretic renography with mercaptoacetyltriglycine (MAG3) from 6 to 8 weeks of age: differential function and drainage. Function under 40% on the affected side, or a fall in function of over 5 to 10% on repeat, suggests significant obstruction.
• Magnetic resonance urography in older children and adults for anatomy and function.
• Urinalysis, culture, creatinine. Urodynamics when bladder dysfunction is suspected.

Differential diagnosis.

• Refluxing megaureter
• Posterior urethral valves
• Neurogenic bladder
• Ureterocele and ectopic ureter
• Pelviureteric junction obstruction
• Ureteric stone or stricture
• Duplex system with obstructed upper pole

• Most are managed without surgery, with about 70 to 90% resolving or stabilising.
• Antibiotic prophylaxis for infants with significant dilatation: amoxicillin 10 mg/kg orally once daily at night for infants under 3 months, then trimethoprim 2 mg/kg (maximum 100 mg) orally once daily at night. Stop at about 12 months if ultrasound is stable and there are no infections.
• Treat febrile infections with culture directed antibiotics.
• Surgery indications: recurrent febrile urinary infection despite prophylaxis, differential function under 40% or a decline of over 5 to 10%, worsening dilatation, pain, or stones.
• Temporary drainage in infants with infection or poor function: ureteric stent, endoscopic balloon dilation, or cutaneous ureterostomy.
• Definitive repair, usually after 6 to 12 months of age: excision of the aperistaltic segment, tapering of the dilated ureter where required, and ureteric reimplantation (intravesical or extravesical), with success of about 90 to 95%.
• Perioperative cefazolin 25 to 30 mg/kg intravenously (maximum 2 g) as a single dose, with paracetamol 15 mg/kg every 6 hours (maximum 60 mg/kg daily).
• Adults: treat symptoms and stones, with reimplantation for obstruction or recurrent infection.

Special groups. Bilateral disease and solitary kidney need lower thresholds for early intervention.

Monitoring. Ultrasound every 3 to 6 months in the first 2 years, then yearly. Renography at 3 months, then at 6 to 12 months if dilatation persists. Creatinine, blood pressure and urine for protein yearly.

Referral and escalation. Refer to paediatric urology. Urgent referral for febrile infection with obstruction, sepsis, bilateral disease with renal impairment or fall in function.