Lipidized and aneurysmal fibrous histiocytoma with epithelial cysts on the left calf

Dear Editor, Benign fibrous histiocytoma (FH) is a well-known mesenchymal tumor composed of a mixture of fibroblastic and histiocytic cells. Several variants exist such as cellular, epithelioid, atrophic, aneurysmal and lipidized. Of these, aneurysmal FH and lipidized FH are considered rare variants and are observed in less than 2% of FH. Here, we report an extremely rare case of FH which showed features of both the aneurysmal and lipidized variants. A 59-year-old Japanese man was referred to our hospital for the evaluation of a tumor on the left calf. The tumor had developed 20 years before presentation and had gradually enlarged. Physical examination revealed a well-circumscribed tumor, 10.0 cm 9 10.4 cm 9 7.9 cm in size, with partial erosion (Fig. 1a). Incisional biopsy suggested a fibrous histiocytic tumor, however, malignancy was not excluded because of its large size, and magnetic resonance imaging (MRI) suggesting abundant blood flow and heterogeneous enhancing signals (Fig. 1b). The tumor was surgically removed with a 1-cm margin and the defect was covered with a full-thickness skin graft. The tumor was well-circumscribed and was not continuous with muscle (Fig. 1c). Histopathologically, the tumor comprised spindle cells and foam cells surrounded by hyalinized collagen bundles, which are typical features of lipidized FH (Fig. 1d).