Hepatocellular Adenoma

Excerpt

Hepatocellular adenoma (HCA), otherwise known as hepatic adenoma, is a rare, benign epithelial hepatic neoplasm often linked to exogenous estrogen intake, usually in the form of oral contraceptive pills. The lesion is also associated with steroid abuse, Fanconi anemia, aplastic anemia, metabolic syndrome, and glycogen storage disease (GSD). HCAs are benign but are at high risk of hemorrhage and malignant transformation.

Although typically solitary, multiple adenomas can occur. Hepatic adenomatosis refers to the presence of 10 or more tumors. Advances in radiologic diagnosis and subtype classifications based on molecular behavior have emerged, which provide a more systematic approach to treating patients with hepatic adenomas. Elective resection is recommended in men with adenomas regardless of size and in women with adenomas greater than 5 cm.

Liver Anatomy and Histology

The liver is located inferior to the diaphragm and occupies the abdominal right upper quadrant (RUQ). This organ has a complex anatomical configuration crucial for its multifunctional roles. The liver is encased in the visceral peritoneum and extends from the midclavicular line to the right costal margin at the level of the 5th intercostal space. The organ's superoposterior aspect houses the bare area where the diaphragm and inferior vena cava (IVC) converge.

The Couinaud classification subdivides the liver into 8 functionally independent segments based on vascularization, bile duct distribution, and lymphatic drainage. These wedge-shaped segments have apices directed toward the hepatic hilum and receive a single branch each of the bile duct, portal vein, and hepatic artery.

Hepatic veins run between adjacent segments, ultimately draining into the IVC, while the middle hepatic vein delineates the liver's right and left lobes. The right hepatic vein further partitions the right lobe into posterior and anterior segments, while the falciform ligament separates the left lobe into medial and lateral segments. The portal vein horizontally divides segments into superior and inferior sections. Segment I is the caudate lobe, distinguished from other lobes by its unique characteristics, such as a dual blood supply and direct drainage into the IVC. Segments II, III, and IV constitute the left hepatic lobe sections. Segments V, VI, VII, and VIII constitute the right lobe hepatic sections.

The liver's blood supply, primarily from the portal vein, enhances liver imaging during the portal venous phase—a property crucial for diagnostic purposes. Tumors supplied by the hepatic artery exhibit enhanced imaging during arterial phases, a principle utilized in therapeutic interventions like transarterial chemoembolization. Hepatic veins appear as anechoic tubes on ultrasound and drain into the IVC. The portal triad—consisting of portal veins, hepatic arteries, and bile ducts—manifests as echogenic foci within the liver parenchyma.

The hepatic lobule serves as the primary functional unit, comprising hexagonal arrays of hepatocytes surrounding central veins. Hepatocytes organize into cords within lobules, enveloping sinusoids housing Kupffer and stellate cells. The lobule's organization into portal triads ensures efficient blood flow across zones delineated by their proximity to portal tracts or central veins. This alternative organization, known as the portal acinus, delineates functional zones. Zone 1 surrounds portal tracts involved in oxidative metabolism. Zone 3 envelopes central veins primarily engaged in drug biotransformation. Zone 2 exhibits mixed functionality.