Validation of the Iwate scoring system for the stratification of laparoscopic liver resections: An international multicenter study

Introduction: The Iwate difficulty scoring system (DSS) is one of the most widely validated DSS for laparoscopic liver resection (LLR). However, these studies only validated the 4 difficulty levels and did not validate the 12-point difficulty index of the system. To address current limitations in the studies validating the Iwate difficulty scoring system (DSS), we performed an international multicenter study to validate the Iwate DSS across both its four difficulty levels and 12-point difficulty index. Methods: A retrospective cohort study of 22,252 patients undergoing LLR across 64 centers worldwide between 2005 and 2021 was performed. Baseline characteristics and perioperative outcomes were analyzed across the four difficulty levels and 12-point difficulty index of the Iwate DSS. Results: A total of 14,759 patients met the inclusion criteria. The main indications for LLR were hepatocellular carcinoma/intrahepatic cholangiocarcinoma (52.8 %), and metastatic tumors liver (26.5 %). In terms of underlying liver pathology, 5127 patients (34.8 %) had liver cirrhosis, and 1214 patients (8.3 %) had portal hypertension. Intraoperative outcomes (operation time, blood loss, blood transfusion, use of Pringles maneuver and open conversion) and postoperative outcomes (length of stay, morbidity, major complications, and 90-day mortality) significantly increased with stepwise increases across the four difficulty levels (P < 0.001) and 12-point difficulty index (P < 0.001). These trends remained significant following adjustment for baseline characteristics (P < 0.001). Conclusion: The Iwate DSS 12-point difficulty index and four difficulty levels correlated well with LLR difficulty as determined by key surrogate perioperative measures.