[A case of fibrous hamartoma of infancy and a review of the Japanese literature].

A case of fibrous hamartoma of infancy in the left axilla of an 18-month-old boy, is reported with some discussion (citations of references). The tumor was situated in the subcutaneous fatty tissue, and its border was unclear. It was removed easily and found to measure 2.5 X 1.5 X 1.5 cm. Histologically, in addition to the three main components, i.e., trabeculae of fibrous tissue, immature mesenchymal cells with a mucoid matrix and interspersed mature fat, a capillary vasoformative proliferation, peripheral nerve fibers and lymph follicle-like structures mingling with and transforming into one another were noted throughout the tumor. On the basis of these findings, immature mesenchymal cells were considered as having very important roles with regard to the histogenesis of fibrous hamartoma of infancy.