Medial Segment of the Male Liver Posterior Aspect

Description

Posteriorly, the medial segment of the liver (Couinaud segment IV) occupies the paramedian portion of the visceral surface, positioned medial to the gallbladder fossa and lateral to the fissure for the ligamentum teres. Superiorly it approaches the porta hepatis, where the transverse fissure separates it from the caudate lobe (segment I) lying more posterior and cranial. The quadrate lobe corresponds to the inferior part of this medial segment on the visceral surface, bounded anteriorly by the inferior border and posteriorly by the hepatic hilum. Orientation on the posterior aspect matters because segment IV sits at the intersection of surgical surface anatomy and portal inflow territory, a frequent point of reference during cholecystectomy and hepatic resection planning. The medial segment is supplied by segmental branches of the left portal vein and left hepatic artery, and its bile drains toward the left hepatic duct, relationships that explain why hilar dissection or left-sided cholangiocarcinoma can quickly threaten this territory. Small variations in the fissures and the apparent size of the quadrate lobe can mislead learners into thinking in lobes rather than segments. A common teaching trap. Use this illustration in hepatobiliary anatomy blocks, operative atlases describing left hepatectomy or segmentectomy IV, and radiology teaching files when correlating visceral surface landmarks with CT or MRI segmental maps. It also suits manuscripts and patient-facing education that need accurate terminology for the quadrate lobe versus the medial segment (segment IV) in an adult male liver. Anatomical accuracy verified by SciePro's Medical Advisory Board.