Hepatic myelolipoma is a rare, benign fat-containing lesion of the liver, usually asymptomatic and found incidentally. Its diagnosis by imaging remains difficult because of a lack of pathognomonic signs. The definite diagnosis is by resection or biopsy. 

Epidemiology 

Hepatic myelolipomas are extremely rare; only 17 cases have been described in the literature.

Clinical presentation

Hepatic myelolipomas are usually asymptomatic. 

Pathology

These lipomatous tumours of the liver are extremely uncommon. Their composition is a mixture of fatty, muscular, haemopoietic, and vascular tissues and the histopathological spectrum includes angiomyolipomas, lipomas and myelolipomas.

The hepatic myelolipomas consist of adipose and myeloid tissue. Their pathogenesis, including hepatic localisation remains unclear, and an association with liver cell metaplasia has been suggested.

Radiographic features

Ultrasound

Appears as a hyperechoic well-circumscribed, lobulated mass. 

CT

Hypodense mass, with fatty attenuations ranging from -20 to -100 HU. Occasionally, the attenuation value is greater than zero, which is dependent on the relative proportions of fat and other elements in the tumour. 

• unenhanced: lobulated well-circumscribed hypodense mass with fat density
• arterial phase: no enhancement
• portal venous phase: hypodense without enhancement

MRI

Appears as a well-defined mass with a pseudocapsule, heterogeneous fatty architecture and contents. 

Treatment and prognosis

Surgical treatment is reserved for symptomatic patients or in case of diagnostic uncertainty. 

Malignant transformation has not been described.

History and etymology

The first case of a hepatic myelolipoma was described in France by Grosdidier in 1973. 

Differential diagnosis

• hepatic angiomyolipoma
• hepatic lipoma
• hepatic adenoma
• haemangioma
• hepatic adrenal rest tumour
• focal nodular hyperplasia

For a wider range of differentials, read more in our article on fat containing liver lesions.