Purpose: To identify tumor and patient-related risk factors for major complications following renal cryoablation and to develop a model for predicting these adverse events.
Materials and methods: Institutional review board approval and informed patient consent were obtained for this HIPAA-compliant retrospective study. All 398 renal cryoablation procedures performed from 2003 through 2011 were reviewed to identify tumor and patient-related risk factors associated with major complications (Clavien-Dindo classification, ≥ grade III). A scoring system for predicting these adverse events was then developed using risk factor weighting obtained from a multivariate logistic regression model. To internally validate this model, the scoring system was then applied to all 73 renal cryoablation procedures performed during 2012.
Results: Among tumor-related factors evaluated, Maximal tumor diameter (P = .0006) and Central tumor location (P = .02) were significantly associated with major complications. Among patient-related factors evaluated, prior Myocardial infarction (MI) (P = .002) and Complicated diabetes mellitus (P = .01) were significantly associated with major complications. This resulted in the (MC)2 risk scoring system, with (MC)2 risk score = 2.5 points (for tumors ≤ 2.5 cm in maximal diameter) or 0.1 points for each millimeter of maximal tumor diameter (for tumors > 2.5 cm) + 1.5 points (if central tumor location) + 2.5 points (if patient history of prior MI) + 3.0 points (if patient history of complicated diabetes). Mean (MC)2 risk score for all renal cryoablations was 4.7 (standard deviation, 1.9; range, 2.5-15.3). The observed major complication rates were 2.0% (95% confidence interval [CI]: 0.6%, 4.6%) in the low-risk group (score < 5.0), 12.8% (95% CI: 7.5%, 19.9%) in the moderate-risk group (score of 5.0-8.0), and 39.1% (95% CI: 19.7%, 61.5%) in the high-risk group (score > 8.0). Application of the (MC)2 scoring system to the validation group yielded a concordance index of 0.82 (95% CI: 0.62, 1.00).
Conclusion: The results of this study suggest that the (MC)2 risk score is a valuable tool for predicting major complications in patients undergoing renal cryoablation. However, external validation is warranted.