A 34-year-old para V woman was referred to our centre at 35+1 weeks of gestation for an assumed fetal malformation with prenatal renal impairment and anhydramnios. Prenatal ultrasound demonstrated unilateral renal agenesis; the bladder was not detectable. The baby was born by caesarian section at 36+2 weeks of gestation because of placental insufficiency. Postnatal adaptation was uneventful, but the newborn presented external stigmas of trisomy 21 and progressive renal impairment with anuria. Nevertheless, the postnatal ultrasound showed two enlarged kidneys in loco typico with impaired perfusion but without signs of malformations. In the lower abdomen, a rosette-shaped structure of unknown origin was noted. Its origin could not be cleared by imaging including voiding cystourethrography and colon contrast radiography. Explorative laparotomy identified the structure as a persistent urachal cyst with secondary obstruction of the upper urinary tract. After removal of the urachus with reconstruction of the bladder dome, renal function recovered completely while urine was drained continuously via suprapubic catheter. A voiding cystourethrogram 3 weeks later showed a posterior urethral valve as an additional unexpected diagnosis. The valve was slit at the age of 6 months without complications, the renal function remained stable in the further course. In retrospect, the main cause for the renal failure remains unclear. It appears to be the obstruction due to the space-consuming character of the urachal cyst, especially because the megacystis typically associated with urethral valve was not viewable. Alternatively, the additional proximal stenosis may have only masked the typical findings of PUV.
