Extramedullary hematopoiesis in pilomatricomas.

We report on seven adult patients with pilomatricomas showing histopathologic findings of extramedullary hematopoiesis. There was no Ovidence of hematological disorders or systemic diseases. Clinically, the lesions appeared to be firm, painless nodules situated on the upper extremities, head, and back. Histopathologically, they represented stereotypical examples of regressive pilomatricomas with relatively small basaloid areas and large masses of cornified eosinophilic material containing shadow cells with variable areas of calcification or ossification. Bone marrow cellular elements, including myeloid and erythroid precursors, and (in two cases) megakaryocytes were present. The finding of extramedullary hematopoiesis in seven (5.8%) of 120 cases of pilomatricomas may suggest that this phenomenon is not uncommon in these neoplasms. Interestingly, hematopoietic infiltrates were histopathologically detected to be contiguous with areas of osseous metaplasia in only two of the seven pilomatricomas in our study. It should further be stressed that extramedullary hematopoiesis in regressive lesions of pilomatricomas is a localized phenomenon and that these findings may not be linked with a systemic hematological disorder. The significance of extramedullary hematopoiesis in pilomatricomas, however, remains to be determined.