A Boari flap is a urological procedure undertaken reimplant the ureter by replacing the distal ureter ureter when this has been destroyed or damaged ( tumor invasion, stricture ).   A tube of bladder tissue is used, being 'pulled''up rather like a ear or the top of a tent, giving a characteristic appearance to the bladder.

In this case a Boari flap has been performed, but the patient has gone on to develop a severe hydronephrosis, from a presumed new stricture.