To present a novel "Hat–Spherical Model" for partial nephrectomy and evaluate its oncological, functional outcomes and complication risks in the application for localized kidney cancer treatment.

Two hundred and ten patients with localized kidney cancer underwent open or laparoscopic "Hat–Spherical" partial nephrectomy from Mar. 2011 to Dec. 2013, and were included for this retrospective analysis. Of the 210 patients, 145 were males and 65 were females. The age ranged from 25 to 78 (56±12) years. The tumor greatest dimension was ≤4.0 cm in 143 cases (68.1%), 4.1–7.0 cm in 49 cases (23.3%) and >7.0 cm in 18 patients (8.6%). According to PADUA (Preoperative Aspects and Dimensions Used for an Anatomical) classification, 90, 86 and 34 patients were respectively stratified as low– (42.9%), intermediate– (40.9%) and high–risk (16.1%) groups. In contrast to traditional technique, the key points of "Hat–Spherical" partial nephrectomy were as follows: after clamping, the renal capsule was incised sharply 3–5 mm away from the tumor edge, and the incision plane was wedge–shaped and towards the tumor pseudocapsule. The "transition zone" between pseudocapsule and normal renal parenchyma was the ideal surgical plane. When reached, the tumor was bluntly separated from the surrounding parenchyma following the natural plane. When close the bottom or approaching the renal sinus, the tumor was enucleated along the pseudocapsule. The positive surgical margin rate, warm ischemic time, complication rate and the postoperative eGFR decline were evaluated. The "Trifecta" criteria, in which the 3 key outcomes of negative cancer margin, minimal renal functional decrease and no urological complications, were applied to evaluate the "Hat–Spherical" partial nephrectomy technique.

Ninety–two patients underwent open "Hat–Spherical" partial nephrectomy. The mean operation time was 120±45 min, the mean warm ischemic time was 15±5 min. The estimated blood loss was 246±188 ml. Twenty–two patients (23.9%) needed renal calyceal repairing. One hundred and eighteen patients underwent laparoscopic "Hat–Spherical" partial nephrectomy. The mean operation time and warm ischemic time were 145±50 min and 23±7 min, respectively. The mean estimated blood loss was 185±120 ml and 30 patients (25.4%) needed renal calyceal repairing. The rate of positive surgical margin was 0.95% (2/210). A total of 42 patients (20.0%) experienced complications during 30 days postoperatively, including 36 ClavienⅠ–Ⅱ minor complications and 6 cases of Clavien Ⅲ–Ⅳ major complications. There were 6 postoperative bleeding events (2.9%) and 4 urine leakages (1.9%). There was no perioperative death. The median (range) follow–up was 18 (10–38) mon. The mean decrease in postoperative eGFR was 9.8±20.4 ml/(min· 1.73 m²), and 62 patients had a greater than 10% reduction in the actual vs volume predicted postoperative eGFR. Until the last follow–up, there was no local recurrence and distant metastasis. Trifecta outcome was achieved in 85 patients (40.5%).

The "Hat–Spherical" partial nephrectomy has three main technical advantages, including safely keeping negative surgical margin, maximal preservation of renal parenchyma and reducing the risk of vessel and renal calyceal injury. The superiority of "Hat–Spherical" technique over traditional partial nephrectomy needs further validation by prospective comparative clinical trials.

Kidney cancer; "Hat–Spherical" partial nephrectomy; Transition zone