Percutaneous nephrolithotomy.

Small mobile stones in the major renal collecting system can be extracted through a percutaneous tract. Initially the radiologist performs a conventional percutaneous needle nephrostomy and inserts a pigtail catheter into the renal pelvis. Over the next week the tract formed is serially dilated to a size large enough to pass a cystoscope into the kidney. The calculi are trapped by a stone basket and removed. The many advantages of this relatively atraumatic procedure are discussed.