Moynihan’s Hump: Our Eyes See What Our Mind Knows
Executive Summary
Moynihan’s hump, also referred to as a "caterpillar hump," is a rare but surgically significant arterial anomaly of the right hepatic artery (RHA). Characterized by a tortuous course that brings the RHA into close proximity with the gallbladder or cystic duct, this variation poses a high risk of misidentification. If the RHA is mistaken for the cystic artery—which is frequently very short in these cases—it may be ligated or injured, leading to severe complications such as ischemic necrosis of the liver or life-threatening hemorrhages. Adherence to established safety protocols, including the "critical view of safety" and the "hug the gall bladder" dictum, is essential for preventing biliary and vascular injuries.
Definition and Anatomical Overview
The standard anatomy of the biliary region involves the gallbladder being supplied by the cystic artery, typically a branch of the RHA that originates behind the common hepatic duct. This artery passes through the Triangle of Calot, defined by:
Superiorly: The inferior surface of the liver.
Laterally: The cystic duct.
Medially: The common hepatic duct.
The Moynihan’s Hump Variation
Moynihan’s hump is a dangerous anomaly where the RHA follows a tortuous "caterpillar turn."
Positioning: The artery takes a loop that brings it close to the gallbladder, often passing in front of (anterior to) the common hepatic duct, though it may also pass posteriorly.
The Cystic Artery Relationship: The length of the cystic artery depends on its origin relative to the hump's loops.
Distal Loop Origin (Common): The cystic artery is very short, arising from the convexity of the loop.
Proximal Loop Origin (Rare): The cystic artery is long and crosses over the tortuous RHA.
Incidence and Surgical Significance
Statistical data indicates that the incidence of Moynihan’s hump of the RHA varies between 1.3% and 13.3%. Despite its rarity, its significance in laparoscopic cholecystectomy is paramount because:
Misidentification: The unusually large, looped RHA is frequently mistaken for a large cystic artery.
Ligation Risks: In attempts to ligate a short cystic artery, the RHA itself may be accidentally ligated or torn.
Proximity: The RHA may supply the gallbladder through several small "twigs," increasing the likelihood of injury during routine dissection.
Clinical Consequences of Injury
Vascular injuries involving the RHA can lead to three primary categories of complications:
Bile duct injury remains one of the most common causes of litigation against abdominal surgeons in the developed world.
Case Study Analysis: Successful Management
A case involving a 55-year-old female with symptomatic cholelithiasis demonstrates the necessity of intraoperative caution. During a laparoscopic cholecystectomy, surgeons identified an "unusually large" cystic artery that appeared to turn back toward the common hepatic duct rather than entering the gallbladder.
Intervention and Outcome:
Consultation: The primary surgeon sought a second opinion from another consultant.
Identification: Further dissection revealed a Moynihan’s hump with a very short cystic artery.
Execution: Dissection was performed cautiously without traction on the cystic artery to create space for ligation.
Critical View: Clips were applied separately to the cystic duct and the short cystic artery only after achieving a "critical view of safety."
Follow-up: The patient was discharged on the second postoperative day with an uneventful two-month follow-up.
Established Safety Rules for Surgeons
To mitigate the risks associated with Moynihan’s hump, the following safety protocols are recommended:
Anatomical Proficiency: Surgeons must possess thorough knowledge of variations. The principle "Your eyes see what your mind knows" highlights that anomalies can only be identified if the surgeon is aware they exist.
Optimal Visualization: Maintain high-quality operative field illumination; in laparoscopy, the camera serves as the surgeon's eyes.
Dissection Dictum: Follow the "hug the gall bladder" rule to stay clear of the deeper structures of Calot's triangle.
Critical View of Safety: Ensure that exactly two—and only two—structures are clearly seen entering the gallbladder before any clipping or ligation occurs.
Ego Management: Surgeons should not hesitate to call for a second opinion or convert to an open procedure if the anatomy remains unclear. Patient safety must take precedence over professional pride.
Conclusion
Every cholecystectomy presents a unique anatomical landscape. Moynihan’s hump serves as a critical reminder that a "standard" procedure can quickly become life-threatening without a rigorous understanding of biliary and vascular anomalies. Safety in these cases is predicated on visual confirmation, meticulous dissection, and the willingness to seek collaborative input when unusual structures are encountered.
