Moynihan's hump of the right hepatic artery in Calot's triangle: a systematic review and meta-analysis of its incidence and surgical importance

Introduction: A rare variation known as "Moynihan's or caterpillar hump" of the right hepatic artery raises the danger of vascular and biliary injuries during hepatobiliary surgery. This research intends to carefully record every case (i.e., patients undergoing laparoscopic cholecystectomy or cadaver dissections) where the right hepatic artery received a caterpillar hump.

Methods: The literature search was conducted with the medical subject headings (MeSH) and EMTREE (subject headings unique to Embase) keywords. The keywords with Boolean operators (OR, AND, and NOT) were used to create search strings in all possible combinations to retrieve bibliographic data. Two authors independently performed a risk of bias assessment and data extraction. The random effects model was used to conduct a meta-analysis.

Results: Thirty studies with a total of 8418 subjects reported that Moynihan's hump was present in 3.81% of them, with a predictive interval of 0.88-16.45%. The incidence of the hump was 3.1% in surgical studies (7496 subjects) and 7.22% (95% CI 4.7-10.93%) in cadaveric data (625 cadavers). Only ten studies addressed the relationship between the caterpillar hump and the common bile duct.

Conclusion: A patient with an unusually "small cystic artery" or "large right hepatic artery" is likely to have a "caterpillar hump". The caterpillar's hump of the right hepatic artery is subject to rare anatomical variations in its course that increase the risk of incorrect vessel ligation or injury during laparoscopic cholecystectomy.