Application of DDD nephrometry score to surgical decision-making for renal tumors

Objective To present a DDD scoring system to access the surgical complexity of renal tumors to assist in the surgical decision-making process. Methods We retrospectively evaluated 561 patients who were histopathologically diagnosed with renal cell carcinoma with available imaging data between January 2013 and September 2017. The surgical approaches, as well as RENAL and DDD scores, were compared. We performed a review of the available English literature published in the last decade and relating to the surgical anatomy pertinent to renal mass excision, and established a solid single renal mass scoring system, the DDD nephrometry score, based on the three most reproducible and pertinent features that characterize the critical anatomical attributes of renal tumors. Each feature in our nephrometry score was designated by an English letter, forming the acronym DDD: (D1)iameter (scores tumor size as the maximal diameter inside the kidney), (D2)epth of the deepest portion of the tumor with the medulla and collecting system or sinus, and (D3) istance (shortest from the mass to the main renal vessels). The points of D1, D2, and D3 were summed as DDD score and tumors were stratified into three complexity levels. The relationships between each D variate and the operation method options were tested by the Mann-Whitney rank sum test. The further Mann-Whitney rank sum test was used to compare the different effects of DDD nephrometry score and RENAL score on surgery method choice. Results In this cohort, 383 (68.3%) patients were men and 178 (31.7%) were women. The mean age was (57.3±11.9) years, and mean BMI was (25.1±3.5) kg/m2. Mean D1 was (4.3±2.0) cm. D2 was 1 pt in 50 (8.9%) patients, 2 pts in 110 (19.6%), and 3 pts in 401 (71.5%). D3 was 1 pt in 357 (63.6%) patients, 2 pts in 33 (5.9%), and 3 pts in 171 (30.5%). There were 36 (6.4%), 186 (33.2%), and 339 (60.4%) patients in the low, moderate, and high DDD score groups, and 140 (25.0%), 289 (51.5%), and 132 (23.5%) in the low, moderate, and high RENAL score groups, respectively. Regarding surgical procedures, 329 (58.6%) patients′ tumors were removed by radical nephrectomy (RN), in which 47 (8.4%) were removed by open radical nephrectomy (ORN) and 282 (50.2%) by laparoscopic radical nephrectomy (LRN); 232 (41.4%) patients′ tumors were removed by partial nephrectomy (PN), in which 32 (5.7%) were removed by open partial nephrectomy (OPN) and 200 (35.7%) by laparoscopic partial nephrectomy (LPN). For partial nephrectomy (PN) rate, significant differences were observed between any two RENAL or DDD score groups (P<0.001 for all), and there was a higher PN rate with the lower score group. Likewise, the same results were observed in the laparoscopic group, and the laparoscopic partial nephrectomy (LPN) rate was higher with the lower score group (P<0.001 for all). As for laparoscopic nephrectomy (LRN) or open nephrectomy (ORN), differences were not significant between low and moderate RENAL or DDD score groups (P=0.135 and P=0.602, respectively), but significant between the low and high groups (P=0.025, <0.018). High DDD score and RENAL groups had significant more patients undergoing ORN than low and moderate groups, respectively. Conclusions DDD score is based on only three variants and all of them are intuitive and pellucid. Even junior urologists and radiologists could easily master this system and it can be measured easily on preoperative CT images. The DDD score could be used to reflect the surgical complexity and assist to make treatment decisions for patients with renal tumors. Key words: Renal cell carcinoma; Surgical procedures; DDD score; RENAL score