Unenhanced computerized axial tomography to detect retained calculi after percutaneous ultrasonic lithotripsy

Purpose: We report our experience with unenhanced computerized axial tomogr aphy (CT) after percutaneous ultrasonic lithotripsy in patients thought to be at high risk for retained calculi. Materials and Methods: CT was obtained in 121 patients (124 kidneys) within 12 to 36 hours of percutaneous ultrasonic lithotripsy for staghorn or larg e nonstaghorn renal calculi. Cases were grouped according to the CT finding s as no retained calculi, insignificant retained calculi (fragments 1 to 3 mm.), retained calculi amenable to shock wave lithotripsy and retained frag ments requiring second look percutaneous ultrasonic lithotripsy or flexible nephroscopy. Results: No calculi were seen in 73 kidneys (59%) and retained calculi were identified in 51 (41%). Shock wave lithotripsy was used to treat 8 patient s and another percutaneous ultrasonic lithotripsy or flexible nephroscopy w as performed in 23 to remove retained stones. Insignificant calculi were no ted in the remaining 21 patients. Conclusions: We believe that postoperative unenhanced CT is superior to pla in renal tomography and is the best method to determine if a patient is sto ne-free after percutaneous ultrasonic lithotripsy. It helps to locate preci sely those stones requiring a second percutaneous ultrasonic lithotripsy or nephroscopic extraction. An unenhanced renal CT devoid of calculi obviates routine postoperative second look flexible nephroscopy. We encourage other s to consider this technique to define more accurately kidney stone status after percutaneous ultrasonic lithotripsy for large staghorn calculi or in any patient at high risk for retained calculi after percutaneous ultrasonic lithotripsy.