Retrograde urethrogram - a novel approach to diagnosing a posterior urethral polyp in a neonate.

We present a case of antenatally detected fetal megacystis caused by an obstructing posterior urethral polyp. Antenatal and postnatal ultrasounds showed bladder wall thickening and bilateral hydroureteronephrosis, most marked antenatally. A working diagnosis of posterior urethral valves was therefore made. However, further postnatal assessment with a micturating cystourethrogram (MCUG) combined with a retrograde urethrogram identified a pedunculated urethral polyp as the cause. The addition of a retrograde urethrogram as an adjunct to the MCUG in the diagnosis of posterior urethral polyp has not previously been reported, and in this case provided diagnostic confidence of this rare condition, allowing for definitive surgical planning.