Evaluation of s.t.o.n.e. nephrolithometry scoring in predicting outcomes of percutaneous nephrolithotomy

Aim: To correlate S.T.O.N.E. Nephrolithometry Score with success and complications after Percutaneous Nephrolithotomy (PCNL).

Materials and Methods: A prospective study conducted at Institute of Urology, Madras Medical College and Rajiv Gandhi Government General Hospital, Chennai, from January 2015 to December 2015. After obtaining informed consent, all patients who underwent PCNL were selected, followed up, their success and complications recorded. Patient with prior treatment for renal calculi , Renal calculi suitable for other modalities of therapy, Patients with contraindications for PCNL, patients who didn’t undergo NCCT KUB in pre-op workup, age <18yrs, BMI >30 were excluded. From NCCT KUB, stone burden, tract length, presence or absence of hydronephrosis, number of calyces involved and stone essence (density) were calculated. This was used to derive the STONE nephrolithometry score. Primary aim was complete clearance of renal calculi by single attempt at PCNL. Operative time, number of tracts dilated, length of hospital stay, postoperative complications and ancillary procedures for complete clearance of calculi were recorded. The data was statistically analyzed.

Results: Complete stone clearance was possible in 147 cases in first session. All cases with score 6, 7 had complete clearance of the calculi. None of the patients with score of 11 or 12 had complete clearance. Mean score of patients who had complete clearance of calculi was 7.46 while those who had incomplete clearance was 10.35. STONE score had a sensitivity of 89.12% and specificity of 98.46% in predicting complete clearance. STONE score was significantly associated with predicting stone free status (p <0.0001). Correlation between STONE score and perioperative parameters was found to be statistically significant. Mean operating time, number of tracts dilated, grade of complications and length of stay all had a positive correlation with total STONE score.

Conclusion: STONE Nephrolithometry scoring is simple and effective bed side tool in determining the chance of achieving stone free status by a single session of PCNL.
Total score, Stone burden, Number of calyces involved were the most important predictors of success after PCNL.