Intraoperative and postoperative outcomes
As shown in Table Intraoperative and postoperative outcomeIn the internal validation data set, 82 (69.5%) patients were classified as the non-difficulty group and 36 (30.5%) were classified as the difficulty group. Compared with the non-difficulty group, the difficulty group had a significantly longer operative time (In the external validation data set, 104 patients and 46 patients were assigned into non-difficulty and difficulty group, respectively. As shown in Table Meanwhile, univariable and multivariable analyses showed that surgical difficulty was the independent risk factor for perioperative mortality (Table S1, Supplemental Digital Content 2, 