Answer: Angiomatoid fibrous histiocytoma

Histology: At low magnification the lesion has a zonal histology. Within the center of the lesion are dilated angiomatous areas filled with blood. Surrounding the blood are bland histiocytic appearing cells with hemosiderin deposition. These cells lack pleomorphism and mitotic activity. External to the histiocytic cells is a prominent lymphoid reaction containing germinal centers.

Discussion: While the histiocytic component could be consistent with benign fibrous histiocytoma, the overall architecture of this lesion differs from this entity. Furthermore, benign fibrous histiocytomas typically have other mixture of cell elements such as foam cells and giant cells. The presence of lymphoid nodules with germinal centers suggests involvement of the lymph node. However, the location of this lesion immediately underneath the skin and the lack of other elements of nodal architecture such as sinuses demonstrate that the lymphoid tissue is merely a reaction to the lesion rather than a lymph node. Hematomas lack such a reaction as seen in the current case. The features seen in this lesion are typical of angiomatoid fibrous histiocytomas. While the vast majority of patients experience a benign clinical course, occasional patients may have local recurrences as well as metastases, similar to plexiform fibrohistiocytic tumor, designated as fibrous tumors of intermediate malignancy. In the past, these used to be designated as angiomatoid malignant fibrous histiocytoma.