Mesenchymal hamartoma of the liver.

Mesenchymal hamartoma is a benign, cystic lesion that arises from connective tissues of the portal tracts. It is most common in children under 5 years of age. The diagnosis can be suspected when a relatively asymptomatic child has a large, smooth mass in the liver. Radionuclide scans demonstrate a solitary lesion, and on ultrasound there are cystic spaces and septa. These are perfectly benign lesions and may be simply enucleated.