The intuitive conclusion that larger kidney stones make for more difficult percutaneous nephrolithotomy is correct.
"The best results from PCNL were achieved with stones smaller than 500 mm2 and the worst results, with stones larger than 2,500 mm2," said first author Burak Turna, MD, of the department of urology at Ege University, Izmir, Turkey. "We saw the best results with pure caliceal stones and the worst results with caliceal component-dominant complex stones."
Ege University maintains a prospective urology database that includes all patients undergoing PCNL, Dr. Turna noted. The research team, led by Oktay Nazli, MD, analyzed data from 234 PCNL patients stratified into six groups by stone burden and into four groups by stone configuration.
The overall stone-free rate for all patients in the study group was 78.6%, Dr. Turna reported, and the combined rate for minor and major complications was 34.6%. In general, Dr. Turna said, increasing stone size was associated with decreasing stone-free rates (p=.0001). Stone-free rates ranged from approximately 85% for stone burden <500 mm2 to approximately 50% for stone burden >2,500 mm2.
Stone configuration also had a notable impact on stone-free rates. Patients who had purely caliceal stones had a stone-free rate of approximately 90%, while the stone-free rate in those who had complex caliceal component-dominant stones was approximately 65%, Dr. Turna said. An increasing caliceal component in complex renal stones was directly associated with decreasing stone-free rates (p=.01).
The impact of stone burden, but not configuration, on complication rates was equally striking. The total number of complications rose in direct proportion to increasing stone size (p=.0001), although the location of stones within the kidney did not affect complication rates (p=.02).
Researchers also found a correlation between increasing stone burden and operative time (p<.05), as well as a greater caliceal component in complex stones and longer mean operative times (p<.01). Increasing stone burden was also associated with multiple tracts (p<.05) and higher blood loss (p=.017). No correlation was noted between blood loss and stone configuration. Increasing stone burden also was associated with rising rates of unplanned secondary procedures (p=.006).
Results of the study have changed the way the researchers approach treatment and counsel their own patients, Dr. Turna said. Those with a lower stone burden generally are good candidates for PCNL, while patients with larger stones are more likely to benefit from more extensive procedures.
"A stone burden of 1,000 mm2 seems to be a threshold for complications," Dr. Turna said. "If the total stone area was higher, the complication rate jumped notably.
"Based on our results, if the patient has more than 2,500 mm2 of stones, you may want to consider other treatment modalities, such as sandwich therapy, laparoscopic, or open nephrolithotomy."