Hepatic adenomas are uncommon benign epithelial liver tumors that develop in an otherwise normal appearing liver. They are seen predominantly in young women (20 to 44 years-old), are frequently located in the right hepatic lobe, and are typically solitary (70 to 80 percent), although multiple adenomas have been described in patients with prolonged contraceptive use, glycogen storage diseases (GSD), and hepatic adenomatosis. Adenomas range in size from 1 to 30 cm. Symptoms such as abdominal pain are more likely with larger lesions (figure 1) .
The prognosis of hepatic adenomas is not well established. However, they have been associated with malignant transformation, spontaneous hemorrhage, and rupture. As a result, their distinction from other types of benign liver tumors is important. This can most often be accomplished using a combination of imaging techniques, although rarely a definitive diagnosis may only be achieved following resection. (See "Solid liver lesions: Differential diagnosis and evaluation".)
ETIOLOGY AND INCIDENCE
Hepatic adenomas are strongly associated with use of oral contraceptives, anabolic androgens, and glycogen storage disease. They are less commonly associated with pregnancy and diabetes mellitus.
The incidence of hepatic adenomas has increased in the last several decades, a trend that coincided with the introduction of oral contraceptives [2-5]. In addition, adenomas are increasingly encountered as incidental findings in patients undergoing ultrasound, computed tomography, or magnetic resonance imaging for unrelated or non-specific symptoms.
Contraceptive use and estrogen therapy — Hepatic adenomas were rarely reported before the advent of oral contraceptives (OCPs) in the 1960s . The association between OCPs and the development of liver tumors was first described in 1973 . Multiple subsequent studies have confirmed this association and have also demonstrated that the development of hepatic adenomas correlated with the dose and duration of hormonal therapy [5,7-10]. The annual incidence is approximately 1 per 1,000,000 in women who have never used OCPs, compared to 30 to 40 per million in long-term users [7,11]. In a study comparing OCP use in 79 women with hepatic adenomas to 220 controls, the largest risk of development of hepatic adenoma occurred in women over the age of 30 years who had used OCPs for longer than 25 months, particularly those who had used OCPs with a high estrogenic component .