Benign liver tumors.

Benign liver tumors are becoming a subject of great interest because increased access to medical care has allowed discovery of many incidental focal lesions. These tumors may be hepatocellular, biliary, or stromal in nature. Several new lesions have been described in recent years causing a need to reassess the pathogenesis and classification of hepatic tumors. Hepatocellular nodules may be neoplastic or a regenerative response to injury. The size and structure of regenerative nodules varies with the distribution and severity of the hepatic injury, leading to a complex classification. Variation in fat content is easily detected on ultrasonography as focal fatty change and focal fatty sparing. Biliary and stromal cells also produce neoplastic or regenerative lesions. Biliary lesions are often cystic in nature. Stromal lesions are varied because of the many nonparenchymal cell types in the liver.