Neoplasms of the liver, either benign or malignant, have characteristic microscopic or gross appearances. Benign tumors of the liver include hemangiomas (the most common), focal nodular hyperplasias, nodular regenerative hyperplasias, and adenomas. Hemangiomas are characterized by numerous small endotheliallined spaces filled with blood. The lack of erythrocytes or blood would raise the possibility of the lesion being a lymphangioma, while pleomorphic or atypical endothelial cells would suggest the possibility of an angiosarcoma. Focal nodular hyperplasia, which has a characteristic gross appearance of a central stellate scar within the tumor, microscopically reveals hepatic nodules surrounded by fibrous bands having numerous proliferating bile ducts. This type of tumor is related to bih-control pills, but has no association with malignancy. In contrast, nodular regenerative hyperplasia involves the entire liver and forms multiple spherical nodules. Histologic sections reveal plump hepatocytes surrounded by rims of atrophic cells. Nodular regenerative hyperplasia is clinically impoant because it is associated with the subsequent development of poal hypeension. Two types of hepatic adenomas are the liver cell adenoma and the bile duct adenoma. Liver cell adenomas are seen in female patients taking bih-control pills. These adenomas may bleed, but are not associated with malignancy. Histologically, cords of hepatocytes are present, but there is no lobular architecture. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition