Clinical Utility of the Difficulty Scoring System for Predicting Surgical Time of Laparoscopic Liver Resection

To the Editor:

We read with great interest the study by Uchida et al. titled: Clinical Utility of the Difficulty Scoring System for Predicting Surgical Time of Laparoscopic Liver Resection. ¹ We congratulate them on their work and for publishing their experience and perspective. They studied 78 patients who underwent laparoscopic liver resection (LLR) and retrospectively assigned a difficulty score as reported by Ban et al. ² They reported that the difficulty score significantly correlated with surgical time and blood loss, but not with morbidity and postoperative hospital stay, and concluded that the difficulty score was found to be an effective predictor of surgical time for LLR. We wish to share our experience as well as clarify some points.

There are questions in their study that may interest readers and clarifications we wish to seek. First, a minor clarification—the LLR scoring system by Ban et al. has an index of 1–12 points and not 1–10 as mentioned, this is evident in Figure 1 as the score goes up to 11. The maximal score is 12 based on the maximal points of each factor—tumor size/proximity to major vessel/liver function—maximal of 1 point each, tumor location—maximal 5 points, and extent of liver resection—maximal 4 points. ²

Second, a sizable proportion (14.1%) of patients in their study consists of patients who had a previous liver resection or had a laparoscopic assisted procedure (83.3%—pure laparoscopic surgery). In our opinion, these patients should be excluded—as being a repeat procedure, depending on the number of adhesions, previous procedure performed, or the proportion and nature of the nonlaparoscopic component; these factors introduce potential confounders to the correlation between the difficulty score and its outcomes such as operative time and blood loss. ³

Third, notably several other outcomes commonly considered as surrogates of operative difficulty were not presented such as blood transfusions requirement, conversion rate, the need for Pringle's maneuver, and its duration (if required). In the same note, it is also not clear the extent on how the difficulty score is able to predict longer operative time. If the score increases by 1 point, how much more operative time is predicted to be required by their analysis. This can be a very useful information, for the surgical time as well as for preoperative planning and patient counseling.

The benefits of LLR is to lessen to some varying degree if the procedure requires more blood loss or operative time than an open approach, but the laparoscopic benefits are completely negated or absent in an event of a conversion. ⁴ Therefore, with this reasoning, we believe that conversions as an outcome should be the important event where one assesses whether various factors including the difficulty score can predict.

There are additional points that deserve to be addressed in their study: (1) Selection bias is inherent in retrospective studies; what were their selection criteria and learning experience for LLR in their practice/institution? (2) What was the correlation between the difficulty levels, in addition to the scores when it was analyzed with respect to their surgical outcomes? (3) It is not clear whether lesions such as liver cysts or gallbladder cancers were included in their study as the difficulty score appears to be based on solid tumors—the tumor size and proximity to major vessels factoring in the score will not be less relevant; likewise, the need for additional procedure such as hilar lymphadenectomy in gallbladder cancer might confound surgical outcomes such as operative time. It will be informative and readers will be interested to know the final pathology of the tumor resections as well. (4) Im et al. also recently validated the score in their experience in laparoscopic left lateral sectionectomy with modifications suggested for those who underwent laparoscopic left lateral sectionectomy for intraductal stones, this is worth a mention in the discussion as well. ⁵