Antenatal mild hydronephrosis with subsequent polyp of the upper ureter in a child presenting with recurrent Dietl's crisis.

We report a 7-year-old boy who had antenatally diagnosed and postnatally confirmed asymptomatic right congenital hydronephrosis secondary to ureteropelvic junction obstruction with the anteroposterior diameter ranging from 7 to 15 mm on serial ultrasound scans till the age of 6 years. He then presented with recurrent attacks of Dietl's crisis almost every month in the seventh year of his life and eluded diagnosis for over a year at various national hospitals, and ended up with an international referral to us. Investigations of the acute attacks clinched the diagnosis of ureteral polyp causing intermittent crisis and he underwent segmental resection and reconstruction in the form of dismembered Anderson-Hyne pyeloplasty with good recovery. Our case revealed that prenatally detected hydronephrosis may worsen after spontaneous postnatal improvement and a polyp acting as a flip valve may produce intermittent hydronephrosis and symptoms later in life. The child should undergo urgent investigations during acute symptoms.