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Sawa et al. Mini-invasive Surg 2024;8:30 https://dx.doi.org/10.20517/2574-1225.2024.43 Page 7 of 11

Figure 3. Surgical and postoperative outcomes compared between OLR and MIS groups in grade I. (A) Operation time is not
significantly different; (B) Blood loss, (C) complication of Clavien Dindo 2 or more, and (D) postoperative hospital stay are better in MIS
group. The numbers of cases of complication of Clavien Dindo 2 or more were 78 cases (34.8%) in OLR and 13 cases (12.4%) in MIS
group (C). OLR: Open liver resection; MIS: minimally invasive surgery.

Minor/major classification has been traditionally used on the basis that a resection of ≥ 3 contiguous
[11]
Couinaud segments is defined as a major resection . New classifications for MISLR were reported by Ban
et al., Wakabayashi et al., Kawaguchi et al., Hasegawa et al., and Halls et al. according to the difficulty of
MISLR [9,17-20] . The classifications proposed by Ban et al., Wakabayashi et al., Hasegawa et al., and Halls et al.
score MISLR procedures according to an index scale [11,17-20] . The three-level complexity classification
proposed by Kawaguchi et al. is simple and based on the type of liver resection procedures. Different from
other classifications, this classification was originally developed for MISLR, and was subsequently validated
[11]
[21]
for OLR and RLR . We used this classification in our current study because it was the only new
classification validated for both MISLR and OLR. Russolillo et al. demonstrated that the classifications
proposed by Kawaguchi et al. and Hasegawa et al. predicted the technical complexity of MISLR better than
classification proposed by Halls et al. . Goh et al. reported that the classifications proposed by
[22]
Wakabayashi et al., Hasegawa et al., and Kawaguchi et al. were significantly associated with surgical
complexity and postoperative outcomes; however, the classification proposed by Halls et al. was not
associated with postoperative outcomes . The analysis of the area under the curve of the receiver operating
[23]
characteristic curve demonstrated that the three-level complexity classification was significantly better than
the minor/major classification for both OLR and MISLR in terms of predicting the operative time, estimated
blood loss, and postoperative complications [10,11] . Furthermore, for MISLR, the classification by Kawaguchi
et al. was similar to that by Wakabayashi et al. in terms of predicting the estimated blood loss and