EXTRAMEDULLARY HEMATOPOIESIS IN PILOMATRICOMAS

We report on seven adult patients with pilomatricomas showing histopat hologic findings of extramedullary hematopoiesis. There was no evidenc e of hematological disorders or systemic diseases. Clinically, the les ions appeared to be firm, painless nodules situated on the upper extre mities, head, and back. Histopathologically, they represented stereoty pical examples of regressive pilomatricomas with relatively small basa loid areas and large masses of cornified eosinophilic material contain ing shadow cells with variable areas of calcification or ossification. Bone marrow cellular elements, including myeloid and erythroid precur sors, and (in two cases) megakaryocytes were present. The finding of e xtramedullary hematopoiesis in seven (5.8%) of 120 cases of pilomatric omas may suggest that this phenomenon is not uncommon in these neoplas ms. 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 stress ed that extramedullary hematopoiesis in regressive lesions of pilomatr icomas is a localized phenomenon and that these findings may not be li nked with a systemic hematological disorder. The significance of extra medullary hematopoiesis in pilomatricomas, however, remains to be dete rmined.