Fusion of the planes of the liver: an anatomic entity merging the midplane and the left intersectional plane.

Background: Alignment of the gallbladder fossa and the round ligament may be associated with an almost unknown portal vein branching anomaly.

Study Design: Ultrasonographic imaging allowed detection of this anomaly, which we characterized as fusion of the planes of the liver. When appropriate, additional specific radiologic examinations were performed (CT scanner supplemented with a three-dimensional reconstruction, a biliary cartography, or an angiography). Surgical consequences were studied from this series and from the literature.

Results: Seven patients (0.5%) had the following criteria: 1) round ligament, gallbladder fossa, and termination of the portal vein occurring in the same plane; 2) typical portal vein branching, including a right posterior branch, left branches, and a main medial branch terminated by the Rex's recessus; 3) two main hepatic veins without a significant middle hepatic vein; and 4) absence of the horizontal part of the left hepatic duct. Fusion of the planes may have been involved in two cases of iatrogenic bile duct injury and contraindicated a tumor resection and a right-liver donation. A review of the literature revealed that lack of recognition of the fusion of the planes led to a high proportion of surgical iatrogenic injury. Fusion of the planes could result from incomplete development of the central part of the liver, in agreement with embryologic knowledge.

Conclusions: Knowledge of the fusion of the planes by hepato-biliary surgeons is important. This anomaly may lead to serious complications if it remains undetected during liver resection or bile duct surgery.