Congenital primary megaureter (ORPHA:617)
A rare non-syndromic urogenital tract malformation characterized by a dilated ureter and normal bladder and bladder outlet. It may be obstructed, refluxing or unobstructed and not refluxing.
Epidemiology
Prevalence is unknown, but primary megaureter (PM) is the second most common cause of neonatal hydronephrosis. The male to female ratio is nearly 4:1. The left side is more often affected than right (1.6-4.5 times). The incidence of obstructed megaureter is 1/10,000.
Clinical description
About half of cases are asymptomatic (most of these unobstructed nonrefluxing) and discovered on routine antenatal ultrasound. PM is usually diagnosed in children but may present in adults. Symptomatic PM presents with urinary tract infections (UTI), 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. Bilateral PM occurs in ~20% of cases and is more likely in children presenting < 1 year old. In unilateral PM, the contra-lateral kidney is absent or dysplastic in 10-15% of patients. ''Obstructed PM'' is the term used when ureteral dilatation due to restricted urinary outflow will cause progressive renal deterioration if untreated.
Etiology
The cause is unknown. It may be due to high fetal urine outflow, changes in the ureter pre-/postnatal or transient anatomical obstructions that improve with postnatal development, such as ureteral folds. Refluxing PM is due to short or absent intravesical ureter, congenital paraureteric diverticulum or other derangement of the vesico-ureteric junction. Obstructed PM occurs when the aperistaltic juxtavesical segment is unable to transport urine at acceptable rates. The cause may be 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 multiple affected members were described.
Diagnostic methods
Diagnosis is based on clinical presentation and confirmed by US. Reflux is diagnosed using voiding cystourethrography. Diuretic renography evaluates urine transport dysfunction. Doppler US, MRI and pressure flow studies have been suggested to 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
Scanning starts at 16-18 weeks of gestation and is repeated depending on the clinical findings. The 28th week is the most sensitive for UT evaluation. Attention must be paid to laterality and grade of dilatation, bladder volume and dynamic of emptying, sex, other malformations, amount of amniotic fluid and echogenicity of the kidneys.
Genetic counseling
At the moment, there is no evidence of genetic cause. Congenital PM can co-occur with other syndromic malformations for which genetic counseling may be indicated (e.g. prune belly, megacystis, Hirschsprung disease, Down syndrome, etc.).
Management and treatment
Antibiotic prophylaxis is started routinely in prenatally detected cases. For refluxing PM, medical management is appropriate during infancy and is continued depending on grade of vesicoureteral reflux and symptoms (UTI and/or renal scars). Surgery is recommended for persistent high-grade reflux in older children. There is no consensus about timing/type of correction; endoscopic subureteric injections of bulking agents or surgical ureteric reimplantation are possible. Nonrefluxing unobstructed PM usually does not require surgery; regular follow-up with antibiotic prophylaxis results in reduction of UT dilation and no deterioration of renal function in 85% of cases. For obstructed PM, surgery is only indicated in cases of significant impairment to urine flow, persistent pain, pyelonephritis, calculi or a decrease in renal function. Temporary endoscopic stenting (with/without previous balloon dilatation) or surgical reimplantation are the preferred options.
Prognosis
PM often resolve spontaneously within the first two years of life, with the maturation of the UT.

                            Last update: 
                            June 2023


                            - Expert reviewer(s): 
                            Pr Marco CASTAGNETTI  - Dr Giovanni MOSIELLO | EUROGEN*


                                * European Reference Network