Histopathology of rare chondroosteoblastic metaplasia in benign lipomas

Lipomas are frequent findings in the routine work of a pathologist. Variants of lipomas are characterized by an additional component, e.g. capillaries in angiolipomas, but ordinarily their classification does not pose any problem. In contrast to the high incidence of lipomas metaplastic formation of cartilage and bone is only rarely seen. This metaplasia is thought to develop on the basis of myxoid and chondroid change within the lipoma. Mechanical stress, trophic disturbances, the conspicuously frequent contact with periosteum and even still unknown factors may represent the causes for the metaplastic transformations. Four own case reports of chondro- and osteolipomas are described and discussed in view of the gross and microscopic findings.