New stone formation: A comparison of extracorporeal shock wave lithotripsy and percutaneous nephrolithotomy

Purpose: There is theoretical concern that stone recurrence rates may be higher following extracorporeal shock wave lithotripsy (ESWL*) compared to other techniques because of residual stone debris. Materials and Methods: We documented all new stone formations in 298 consecutive patients who initially achieved a stone-free status following ESWL for renal calculi less than 2 cm. in largest dimension, and compared the findings to those of 62 patients treated with percutaneous nephrolithotomy without ultrasonic fragmentation. Stone-free status was assessed by a centrally reviewed plain abdominal film and renal tomograms at 3 months. A plain abdominal film was repeated at 12 and 24 months to detect recurrence. Results: New stones formed in 22.2% of patients after ESWL and 4.2% after percutaneous nephrolithotomy at 1 year (p = 0.004), and in 34.8% versus 22.6%, respectively, at 2 years (p = 0.190). Furthermore, more new stones recurred in the lower and mid calices compared to baseline location in the ESWL group (chi-square <0.0001), which was not observed in the percutaneous nephrolithotomy group. Conclusions: Our data support a trend toward higher stone recurrence rates in ESWL treated patients, which may be due to microscopic sand particles migrating to dependent calices and acting as a nidus for new stone formation.