Mesenchymal hamartoma of the liver in the adult: association with distinct clinical features and histological changes.

Mesenchymal hamartoma of the liver (MHL) is an uncommon mass lesion composed of architecturally abnormal bile ducts in an uncommitted myxoid stroma. Most MHL are diagnosed in childhood. More than 50% of cases are seen in the first year of life, although a few cases have been previously reported in adults. The spectrum of pathological findings in the cases presenting in adults, including differences in comparison with MHL in children, has not been fully characterized. In this report, we describe 3 cases of MHL in patients 46, 63, and 66 years of age. Each of the patients was a woman who had a solid or multicystic hepatic mass ranging from 5 to 24 cm in maximum dimension. In contrast to the childhood cases, the stromal component was fibrotic with areas of dense hyalinization and only focal myxoid areas. In 1 case, the mesenchymal component was the predominant feature of the lesion, with only occasional ductal elements identified with thorough tissue sampling. Immunohistochemical analysis with a panel of antibodies showed that, as in normal bile ducts, the ductal structures within the lesion were immunoreactive for cytokeratin 7 and negative for cytokeratin 20. The stroma was composed of a prominent population of fibroblasts and myofibroblasts that were positive for smooth muscle actin and vimentin. Analysis of the current findings, together with the previous case reports, shows that in contrast to MHL in children, this lesion in adults is found more commonly in women who present with abdominal pain. Recognition of the clinicopathologic differences between adult and pediatric cases will facilitate accurate diagnosis of this uncommon lesion.