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IWATE Difficulty Score

Difficulty of Laparoscopic Liver Resection

The IWATE criteria score laparoscopic hepatectomy difficulty across four domains: tumour location, extent of resection, proximity to major vessels, and liver function reserve. Scores classify procedures from Low to Expert difficulty.

HepatobiliaryLaparoscopicSurgical Planning
IWATE Calculator
4 Difficulty Domains
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IWATE Difficulty Score (0–12)

Difficulty Levels

ScoreDifficultyRecommended Approach
0–3LowSuitable for surgeons learning laparoscopic liver surgery (≥20 minor cases)
4–6ModerateRequires experienced laparoscopic liver surgeon (≥60 procedures including major)
7–9HighHigh-volume specialist centre; hybrid or hand-assisted approaches acceptable
10–12ExpertExpert centre only; meticulous case selection; open conversion threshold should be low

Segment Anatomy Reference

Anterolateral (Low difficulty): S2, S3 (left lateral), S4b (inferior left medial), S5 (anterior right), S6 (posterior right inferior)

Posterosuperior (Higher difficulty): S7 (posterior right superior), S8 (anterior right superior)

Highest difficulty: S1 (caudate lobe — retrohepatic, bilateral portal pedicle supply), S4a (superior left medial — proximity to left hepatic vein confluence and middle hepatic vein)

Clinical Application

  • Pre-operative planning: Calculate IWATE score at multidisciplinary team meeting when considering laparoscopic approach for hepatic resection.
  • Learning curve: The IWATE system was developed to guide case selection during the laparoscopic liver surgery learning curve. Low-difficulty cases should be mastered before advancing to moderate/high difficulty.
  • Conversion to open: A pre-operative score does not mandate a laparoscopic approach. Intraoperative factors may necessitate conversion — this should not be considered a complication.
  • Cirrhotic liver: The addition of 2 points for chronic liver disease reflects the increased technical difficulty (fragile parenchyma, harder haemostasis, reduced remnant function reserve) and higher risk of decompensation.
  • Limitations: Tumour size, position within segment, previous surgery, and patient habitus are not explicitly included in the 4-factor IWATE score — these should be considered alongside it in decision-making.
  • Companion score: The IWATE score should be used alongside functional assessment (ICGR15, future liver remnant volume) and oncological staging for comprehensive pre-operative planning.

References

  1. Kawaguchi Y, et al. Validation of the IWATE criteria as an efficient difficulty scoring system for laparoscopic liver resection. J Hepatobiliary Pancreat Sci. 2015;22(5):378–385.
  2. Kawaguchi Y, et al. Predictors of difficulty in laparoscopic liver resection: a systematic review and meta-analysis. Ann Surg. 2018;267(5):845–853.
  3. Halls MC, et al. Establishment of the Southampton Difficulty Score for laparoscopic liver surgery. Surg Endosc. 2018;32(3):1457–1463.

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