To validate the Iwate difficulty scoring system and Institut Mutualiste Montsouris (IMM) scoring system (Appendix 2) in both laparoscopic and robotic liver resections

Minimally-invasive liver resections (MILR) are increasingly conducted world-wide today. Several international consensus meetings were convened to enable the safe dissemination of laparoscopic and robotic liver resections. The Iwate difficulty scoring system (Appendix 1) was formulated in Japan to grade the difficulty of liver resections. This was to allow beginners to adopt a stepwise approach to safely perform MILR according to their experience and competency level. Although this system has been recently validated in a recent Japanese multicenter study, it has not been externally validated in a large cohort of patients. Thus far, it has only been validated in several small single center studies. Furthermore, its utility for robotic liver resections has not been well-studied.

Inclusion Criteria:

• All consecutive patients operated at a single institution during a fixed period
• Most recent operation date allowed (up till December 31, 2020, to allow three months follow-up).
• All minimally invasive hepatectomy approaches can be included, including lap- assisted (hybrid), hand-assisted, robotic-assisted and pure laparoscopy.
• The data of all patients including those that had repeat liver resections, concomitant surgeries (e.g. colectomies, hilar lymph node dissection, enbloc resections) may be included
• Patients with no "liver tumors" such as recurrent pyogenic cholangitis/ gallbladder may be included
• The site of the "lesion/ pathology" will be considered as the tumor site, size will be considered less than 3 cm unless tumor invades the liver.

Exclusion Criteria:

• • Patients < 18 years of age

  • Patients with liver transplant living donor hepatectomies

Hospital of patients who underwent Minimally Invasive Liver Resection from January 1, 2000 to December 31, 2020.