A 4-year-old girl presented with urinary infection with E.coli, pus cells in urine, dilatation of left ureter with hydroureter ; micturating cysto-urethrogram shows a filling defect in the bladder. What is the likely diagnosis?

A ureterocele is a cystic dilatation of the terminal ureter and is obstructive because of a pinpoint ureteral orifice. Ureteroceles are much more common in girls than in boys. In girls, ureteroceles are almost always associated with ureteral duplication, whereas in 50% of affected boys there is only one ureter. Ultrasonography is effective in demonstrating the ureterocele and whether the associated obstructed system is duplicated or single. VCUG usually shows a filling defect in the bladder, sometimes large, corresponding to the ureterocele, and often shows reflux into the adjacent lower pole collecting system with typical findings of a "drooping lily" appearance to the kidney. Nuclear renal scintigraphy is most accurate in demonstrating whether the affected renal moiety has significant function.