Hemangioma is the most common benign tumor affecting the liver.  Hepatic hemangiomas are mesenchymal in origin and usually are solitary. Some authorities consider them to be benign congenital hamartomas. Hemangiomas are composed of masses of blood vessels that are atypical or irregular in arrangement and size.
The etiology of these lesions remains unknown, although oral contraceptives and steroids may accelerate the growth of a hemangioma. Whether or not these drugs actually induce the formation of the hemangioma is unclear.
Although no definite familial or genetic mode of inheritance has been described, Moser et al reported a large family of Italian origin in which 3 female patients in 3 successive generations had large symptomatic hepatic hemangiomas.  The authors postulated that restriction of the disease to the female sex could be explained by sex-dependent differences in penetrance, the expression of a presumed liver-hemangioma gene, or the production of proliferative factors, such as female sex hormones.
Several pharmacologic agents have been postulated to promote tumor growth. Steroid therapy,  estrogen therapy, and pregnancy  can increase the size of an already existing hemangioma. One study prospectively evaluated 94 women with hepatic hemangiomas, with a mean follow-up period of 7.3 years (range, 1-17 y).  An increase in the size of the hemangiomas was seen in 23% of women who received hormonal therapy as opposed to 10% of control subjects (P=0.05). Hemangiomas have also been reported in pregnant women following ovarian stimulation therapy with clomiphene citrate and human chorionic gonadotropin. 
United States data
The reported incidence rate of hepatic hemangiomas is approximately 2%. The prevalence rate at necropsy is as high as 7.4%. The widespread use of noninvasive abdominal imaging modalities has led to increased detection of asymptomatic lesions in vivo.
Sex- and age-related demographics
Women, especially with a history of multiparity, are affected more often than men. The female-to-male ratio is 4-6:1.
Hepatic hemangiomas can occur at all ages, but most are diagnosed in individuals aged 30-50 years. Female patients often present at a younger age and with larger tumors.
Overall, a patient with a hepatic hemangioma has an excellent prognosis. Malignant transformation has not been described.
Complications depend on the size and location of the tumor. It needs to be emphasized that the following complications are rarely described:
Rupture with resultant hemoperitoneum: Rarely, large tumors rupture spontaneously or after blunt trauma. Patients may present with signs of circulatory shock and hemoperitoneum.
Compression of bile ducts and nearby arteries and veins: One case has been reported of lower extremity edema caused by compression of the inferior vena cava by a cavernous hemangioma of the caudate lobe of the liver.
Gastric compression: Early satiety, nausea, and vomiting may occur when large lesions compress the stomach, producing gastric outlet obstruction.
High-output congestive heart failure