Congenital Primary Megaureter

Congenital primary megaureter (PM) is an idiopathic condition in which the bladder and bladder outlet are normal but the ureter is dilated to some extent. It may be obstructed, refluxing or unobstructed and not refluxing.

Epidemiology

Prevalence is unknown, but PM is the second most common cause of neonatal hydronephrosis. The male to female ratio is nearly 4:1 and the left side is more often affected than right (1.6-4.5 times). The majority of cases are nonrefluxing and unobstructed. The incidence of obstructed megaureter is 1/10,000.

Clinical description

Bilateral PM occurs in about 20% of cases and is more likely in children presenting before one year old than in older patients. In unilateral PM the contra-lateral kidney is absent or dysplastic in 10-15% of patients. PM is more commonly diagnosed in children but may present in adulthood (PM adult form; see this term). About half of cases are asymptomatic and are discovered on routine antenatal ultrasound. Most asymptomatic patients have unobstructed PM. When symptomatic, PM presents with urinary tract infections, hydronephrosis, fever and abdominal and flank pain. Microscopic hematuria is frequent, may occur without infection and may indicate calculus formation. Patients rarely present with signs of renal failure. Most PM in neonates is nonrefluxing and unobstructed.

Etiology

The cause is unknown but it may be due to high fetal urine outflow, changes in the ureter pre- and postnatal or transient anatomical obstructions that improve with postnatal development, such as ureteral folds. Refluxing PM is caused by a short or absent intravesical ureter, congenital para-ureteric diverticulum or other derangement of the vesico-ureteric junction. It may be associated with megacystis megaureter syndrome and prune belly syndrome (see this term). Obstructed PM is a functional obstruction arising from an aperistaltic juxtavesical segment 0.5-4cm long that is unable to transport urine at acceptable rates. Causal theories include excessive collagen deposition, hypertrophy of ureter muscle, thick periureteral tissues or a circumferential segment devoid of muscle. PM is not known to be hereditary, but families with more than one affected member have been described. PM may be associated with renal agenesis, megacalycosis (see these terms) and urolithiasis.

Diagnostic methods

Diagnosis is based on clinical presentation and ultrasound before and after birth, and is confirmed by intravenous urography (IVU) and radioisotope renography. Reflux is diagnosed using voiding cystourethrography. Renal scintigraphy, Doppler ultrasound (DUS) and pressure flow studies determine obstruction.

Differential diagnosis

Differential diagnoses include causes of secondary megaureter (polyuria (diabetes insipidus), infection, bladder outlet obstruction, neuropathic bladder, infravesical obstruction or extrinsic lesions).

Antenatal diagnosis

Antenatal diagnosis is based on ultrasound showing hydronephrosis, followed by postnatal confirmation.

Management and treatment

Treatment depends on the type of PM. For refluxing PM, medical management is appropriate during infancy and is continued if there is a trend to resolution. Surgery is recommended for persistent high-grade reflux in older children and adults. Nonrefluxing unobstructed PM usually does not require surgery as expectant treatment (regular follow-up with antibiotic prophylaxis for urinary tract infections) results in reduction of urinary tract dilation and no deterioration of renal function. Management of obstructed PM involves monitoring of symptoms and renal function. Surgery is indicated in cases of significant impairment to urine flow, persistent pain, pyelonephritis or calculi or a decrease in renal function. Antibiotic prophylaxis is started routinely after delivery in cases with prenatally detected hydroureteronephrosis and is continued after diagnosis and surgical repair.

Prognosis

Many cases of PM resolve spontaneously within the first two years of life, with the maturation of the urinary tract.