Three-dimensional topology-based T-index as an indicator of surgical difficulty of partial nephrectomy in patients with small renal mass.

Purpose: To accurately describe the three-dimensional topology of renal tumors, our study suggests a new nephrometry scoring system, the T-index, that combines information about intraparenchymal extension and peripherality of the renal tumor.

Materials and methods: This study included 113 patients who underwent partial nephrectomy for small clear cell renal cell carcinoma between 2007 and 2014. Manual segmentation of the renal parenchyma, sinus, and tumor was performed using preoperative computed tomography images. The T-index was calculated by adding the reciprocals of the distances from all points on the tumor-parenchyma interface to the renal sinus. Correlations with perioperative factors and the impact of the T-index on postoperative complications were evaluated and compared with existing nephrometry scoring systems (PADUA, RENAL, contact surface area [CSA], and C-index).

Results: The mean value of the T-index among the 113 patients was 116.1±100.5 (1/mm). The T-index showed the strongest correlation with perioperative factors compared with other nephrometry scoring systems. The T-index was able to predict the risk for postoperative complications, either overall (p=0.015) or major complications (p=0.030). A predictive model based on the T-index of the overall postoperative complications presented the best performance (area under the curve, 0.692; 95% CI, 0.599-0.776) compared with other nephrometry scoring systems.

Conclusions: The T-index can be considered as a single value comprising key structural indicators for surgical complexity. Our findings suggest that the T-index can provide a quantitative and objective scoring system associated with surgical difficulty and postoperative complications of partial nephrectomy.