STONE DISEASE

Intraoperative Fragment Detection during Percutaneous Nephrolithotomy: Evaluation of High Magnification Rotational Fluoroscopy Combined With Aggressive Nephroscopy
Portis AJ, Laliberte MA, Drake S, Holtz C, Rosenberg MS, Bretzke CA
Metropolitan Urologic Specialists P. A., St. Paul, Minnesota, USA
J Urol. 2006; 175: 162-5; discussion 165-6

• Purpose: Percutaneous nephrolithotomy effectively treats large volume renal calculi but relies on postoperative imaging to judge success. We evaluated the effectiveness of maximizing intraoperative imaging through combined high resolution fluoroscopy and flexible nephroscopy.
• Materials and Methods: Percutaneous nephrolithotomy was performed cooperatively with a radiologist in an interventional radiology suite equipped with a ceiling mounted, high resolution C-arm. Aggressive rigid and flexible nephroscopy was performed. At the conclusion patients were prospectively classified as radiologically and/or endoscopically stone-free. Postoperative noncontrast CT allowed fragment classification as stone-free, 2 mm or less, 2 to 4 mm and greater than 4 mm.
• Results: The average stone dimension +/- SEM was 579 +/- 77 mm(2) in 25 consecutive renal units. CT demonstrated that 15 renal units (60%) were stone-free after the primary procedure, while 2 (8%), 5 (20%) and 3 (12%) had fragments 2 or less, 2 to 4 and greater than 4 mm, respectively. Of 21 renal units considered endoscopically and fluoroscopically stone-free postoperative CT demonstrated that 6 had residual fragments, of which all were less than 4 mm. All 4 renal units not considered radiologically and endoscopically stone-free had fragments on CT. Intraoperative fluoroscopy after nephroscopy demonstrated fragments in 36% of renal units, of which after further nephroscopy 78% were stone-free on CT. The sensitivity of intraoperative imaging with reference to the gold standard of postoperative CT was 40%, 38% and 100% at thresholds of 0, 2 and 4 mm, respectively. Specificity was 100%, 94% and 95%, respectively.
• Conclusions: Flexible nephroscopy combined with high magnification rotational fluoroscopy allows sensitive and specific intraoperative detection of residual fragments, enabling immediate removal or the planning of necessary second look nephroscopy.
  
  
• Editorial Comment
  The benefit of achieving a stone free state after surgical stone procedures has been amply demonstrated by Streem and others who showed that even small residual stones are associated with a high likelihood of stone growth, eventual development of symptoms or the need for surgical intervention (1). As such, the identification of residual fragments and aggressive removal is strongly encouraged. Unfortunately, accurate identification of residual fragments is typically performed postoperatively, necessitating a second procedure to remove remaining fragments. However, Portis and colleagues showed that the use of high magnification rotational fluoroscopy along with flexible nephroscopy could improve the detection and removal of residual fragments at the time of initial percutaneous nephroscopy and potentially reduce the need for a second operative intervention. With the use of this technique in 22 patients and 25 renal units, 7 of 9 renal units in which residual fragments were detected by high magnification fluoroscopy after endoscopic inspection were rendered stone free. Postoperative CT confirmed a stone free state in 15 of 21 renal units thought to be endoscopically and radiographically stone free, and demonstrated < 4 mm residual fragments in the remaining 6.
  This technique results in a 3-4 fold higher stone free rate after initial PCNL for large stones than has been reported in series in which standard fluoroscopy and flexible nephroscopy were utilized in conjunction with rigid nephroscopic debulking at the time of initial PCNL. Pearle and colleagues achieved a 20% or 32% stone free rate depending on whether CT or flexible nephroscopy was used as the gold standard for residual fragments (2). Consequently, the need for reoperation is substantially reduced by the use of this aggressive radiographic and endoscopic regimen.

References
1. Streem SB, Yost A, Mascha E: Clinical implications of clinically insignificant stone fragments after extracorporeal shock wave lithotripsy. J Urol. 1996; 155: 1186-90.
2. Pearle MS, Watamull LM, Mullican MA: Sensitivity of noncontrast helical computerized tomography and plain film radiography compared to flexible nephroscopy for detecting residual fragments after percutaneous nephrostolithotomy. J Urol. 1999; 162: 23-6.

Dr. Margaret S. Pearle
Associate Professor of Urology
University of Texas Southwestern Med Ctr
Dallas, Texas, USA