S15C2P4-3:Red arrows identify histiocytes with enlarged nuclei that are deeply cleaved. There is nuclear atypia; the lesion was classified as an atypical xanthogranuloma, or atypical histiocytoma. Acidophilic inclusions of cytoplasm  are present in some of the nuclei.

S15C2P4-4: There are scattered multinucleated giant cells, but they are not touton type. The nuclei of histiocytes are mostly bland, but some are indented. In the area with lymphoid cells, centrally and to the left, many of the histiocytes are of migratory type. The changes would suggest an active recruitment of histiocytes into the lesion in this area; the lesion in this area is “immature.”

S15C2P4-5: An immunoreaction for S100 protein shows scattered positive dendritic cells among the histiocytes.

S15C2P4-6: At a margin of the lesion,  S100 protein (+) dendritic histiocytes are richly distributed among collagen bundles of the reticular dermis. Click the navigation bar, “next page in sequence” to go to next page; this Case is continued on the next page.