Minimally Invasive Lymphadenectomy for Biliary Tumors: Stepwise Progress

Abstract

A recent issue of Annals of Surgical Oncology contains a study that reports the perioperative and long-term outcomes of laparoscopic lymphadenectomy for biliary tract tumors (intrahepatic cholangiocarcinoma and gallbladder cancer). Ratti et al. used propensity score matching to compare laparoscopic and open lymphadenectomy for biliary tract tumors, and attempted to isolate the lymphadenectomy-related outcomes from the concomitant hepatobiliary resection. They reported lower overall and lymphadenectomy-related morbidity in the laparoscopic group, while the number of retrieved lymph nodes and long-term oncologic outcomes were similar between groups. The authors, who are true experts in the field, should be commended for their efforts to push minimally invasive techniques forward in hepatobiliary surgery. Propensity score matching and instrumental variables are methodologies used to address selection bias, and are commonly encountered in surgical observation studies. The validity of these methods depends on which variables are used to predict the propensity score. Although propensity score matching can assist with the statistical control of known factors, it does not control for unknown factors or factors not included in the matching process. In this study, eight variables were selected for matching: age, American Society of Anesthesiologists (ASA) score, diagnosis, underlying liver disease, radiological nodal status, nodularity, tumor dimensions, T stage, and extent of hepatectomy. The chosen variables are important to determine whether the patient is a surgical candidate and to define the magnitude of the operation, but, with the exception of the radiological nodal status, have little to do with a laparoscopic lymphadenectomy. Variables that are perhaps more important to the laparoscopic lymphadenectomy component of the procedure, albeit more difficult to quantify, such as presence of vascular and biliary anatomic variants, surgeon experience, and laparoscopic hepatobiliary surgical volume, were not included in the matching process. Omission of confounding variables such as these from a propensity score analysis may lead to significantly biased results. Another common pitfall of propensity score analyses of surgical procedures is the accounting of crossover procedures (i.e. a procedure that was started as laparoscopic and converted to open). Obviously, crossover procedures should be analyzed with intent-to-treat principles, but most commonly this is not the case in retrospective surgical observational studies. Selection of variables for propensity score matching, and accounting for crossover procedures, are only a couple of many methodological issues that must be considered and reported in a propensity score analysis. It is imperative that an individual with statistical expertise be involved with the construction and design of a propensity score analysis. Expert hepatobiliary surgeons have detailed knowledge of hepatobiliary anatomy, extensive surgical experience, and sound clinical judgment. Only about 60% of patients have ‘normal’ (type I) hepatic arterial anatomy as is frequently reproduced in anatomy texts such as Netter; 10 different variations of arterial anatomy have been described (i.e. replaced right hepatic artery, accessory left, etc.). The knowledge and recognition of these variations is essential for safe hepatobiliary surgery. Most variations in biliary and portal venous anatomy are encountered in an intrahepatic and perihilar location and are less relevant to a hepatoduodenal ligament lymphadenectomy, but failure to appreciate these variations during hepatobiliary resections can result in catastrophic complications. Lymphatic drainage of the gallbladder, as initially described by Ito et al., Society of Surgical Oncology 2019