Atresia of urethra (ORPHA:105)
A rare fetal lower urinary tract obstruction (LUTO) characterized by closure or failure to develop an opening in the urethra and resulting in obstructive uropathy presenting in utero as megacystis, oligohydramnios or anhydramnios, and potter sequence.
Epidemiology
Prevalence is unknown, but is higher in males than females.
Clinical description
Atresia of urethra often presents on routine antenatal ultrasound with megacystis, oligohydramnios or anhydramnios and sometimes urinary ascites. It may cause fetal death. In cases that survive to birth, additional symptoms include respiratory insufficiency due to pulmonary hypoplasia, megaureter, hydronephrosis and enlarged often cystic and functionally impaired/non-functional dysplastic kidneys as well as abdominal distention. Furthermore, a Potter sequence can be found due to oligo- or anhydramnios. Patients may present with patent urachus or vesicocutaneous fistula.
Etiology
The etiology of atresia of the urethra is unknown. Common clinical features arise from the inability of urine to pass out of the body of the fetus, resulting in oligohydramnios which in turn affects the development of the lungs and causes features of Potter sequence. Congenital obstruction of the urinary tract at a critical time in organogenesis has a profound and lifelong effect on kidney, ureteral and bladder function. In rare cases, there is an abnormal opening between the bladder and the rectum which may allow the urine to drain.
Diagnostic methods
Antenatal diagnosis is based on ultrasound. By then it is not possible to clearly distinguish between different forms of LUTO. If megacystis occurs in early pregnancy (around 17 weeks of gestation) atresia of the urethra is more likely to be a possible underlying cause then in later gestation. Postnatally, micturating cysto- urethrography and/or cystoscopy can be used for final diagnosis and differentiation between atresia of the urethra and other forms of LUTO as differential diagnosis.
Differential diagnosis
Differential diagnoses include other causes of megacystis including posterior urethral valve, anterior urethral valve, urethral stenosis, urethral agenesis, double urethra, cloacal malformation and, in rare and severe cases, different forms of voiding dysfunction or megacystis megaureter syndrome. Atresia of urethra can occur in combination with several other conditions including caudal dysplasia, cloacal extrophy, DiGeorge syndrome, prune belly syndrome, Fraser syndrome, cryptophtalmus, Johnson-Munson, Meckel-Gruber, Sirenomelia, and Townes-Brocks syndrome.
Antenatal diagnosis
Antenatal diagnosis is based on ultrasound evidence of megacystis and oligohydramnios. Fetal MRI can be used to attempt confirmation of the diagnosis.
Genetic counseling
If atresia of the urethra occurs together with other birth defects, genetic counselling should be considered. For isolated atresia of the urethra no genetic causes are known so far.
Management and treatment
Antenatal treatment involves urinary decompression with a vesico-amniotic shunt. If the antenatal period is survived, postnatal treatment depends on the pulmonary and renal function. All cases with remaining renal function require a suprapubic urine drainage until reconstructive surgery. Successful treatment of severe cases (obstructive uropathy, kidney failure and pulmonary hypoplasia) with extra corporal membrane oxygenation (ECMO) therapy and hemofiltration/peritoneal dialyses has been described.
Prognosis
The malformation usually results in fetal death without surgical intervention. Prenatal decompression allows survival and may even lead to normal bladder and renal function. Nevertheless, progression into kidney failure is common. Extensive surgical reconstruction is to be expected.

                            Last update: 
                            July 2020


                            - Expert reviewer(s): 
                            Dr Alina HILGER