Chapter 66: Liver Anatomy

The liver typically presents a reddish-brown hue, changing color or texture with conditions such as fatty deposition (yellowish tinge) or venous outflow obstruction (bluish tinge). Grossly, the liver is wedge-shaped and resides mainly in the right hypochondriac and epigastric regions. Its surfaces are divided into the superior, anterior, and right continuous diaphragmatic surface, which is shaped by the diaphragm and related to the ribs, lung, and pleura, and the inferior (visceral) surface, which contacts adjacent viscera like the stomach fundus, duodenum, right kidney, and right suprarenal gland. The liver is stabilized by primary suspensory factors, including the inferior vena cava (IVC) and major hepatic veins, as well as several peritoneal attachments, such as the falciform, coronary, and triangular ligaments. The falciform ligament contains the round ligament of the liver, which is the remnant of the fetal left umbilical vein. Historically divided into four external lobes (right, left, caudate, and quadrate), modern surgical anatomy employs Couinaud’s functional segmentation, which organizes the liver into eight segments based on the distribution of the portal venous branches. These divisions are defined by major internal fissures that contain the hepatic veins: the main portal fissure (Cantlie’s line) houses the middle hepatic vein and separates the right and left hemilivers; the left portal fissure contains the left hepatic vein, separating the left medial and lateral sectors; and the right portal fissure contains the right hepatic vein, separating the right anterior and posterior sectors. The caudate lobe, corresponding to Segment I, is functionally separate and typically drains directly into the IVC by multiple small tributaries. The porta hepatis, a deep fissure, transmits the portal triad—composed of the hepatic portal vein (which conveys blood from the gastrointestinal tract), the hepatic artery (with frequent anatomical variants), and the hepatic ducts—surrounded by perivascular fibrous capsules (Glissonian sheaths). Knowledge of anatomical variations in the hepatic artery and portal vein is crucial for surgical procedures, such as liver transplantation and tumor resection. Microscopically, the liver is structured around functional units called acini, which show metabolic heterogeneity across three zones related to blood flow direction. The parenchyma consists primarily of polyhedral hepatocytes, arranged in plates separated by sinusoids. The sinusoids are lined by highly fenestrated endothelial cells, allowing plasma access to the perisinusoidal space (of Disse), and contain specialized stellate macrophages (Kupffer cells) responsible for phagocytosis and immune clearance. Hepatic stellate cells, which store Vitamin A, reside in the space of Disse and contribute to fibrosis and cirrhosis following liver injury. Bile secreted by hepatocytes collects in canaliculi and flows outward toward the portal tracts, opposite to the centripetal blood flow. Increased pressure in the portal system results in portal hypertension, leading to the development of porto-systemic shunts (anastomoses) at several sites, clinically manifesting as esophageal varices, rectal varices, or "caput medusae".