Hemosiderotic fibrohistiocytic lipomatous lesion: Ten cases of a previously undescribed fatty lesion of the foot/ankle

We address the clinicopathologic features of a previously undescribed heavi ly-pigmented spindle cell proliferation within a circumscribed benign lipom atous lesion that occurs mainly in the ankle region of older females. Patie nts with "lipoma with fibrohistiocytic proliferation" were retrieved from o ur files. Slides and clinical information were reviewed, and immunohistoche mistry was performed (n = 5). Ten patients with hemosiderotic fibrohistiocy tic lipomatous lesions were identified. All cases demonstrated a well-circu mscribed fatty lesion with random focal proliferations of plump, slightly p leomorphic spindled cells, scattered inflammatory cells, and abundant iron pigment. The spindled cells had vesicular nuclei with indistinct nucleoli; occasional hyperchromatism was observed. No nuclear cytoplasmic inclusions were identified. The spindled component had a reactive appearance. In most cases, the fatty component, with homogeneously sized adipocytes, predominat ed. The lesions occurred in the foot/ankle region (8/10, one each cheek and hand) of primarily females (8/10) with a mean age of 50.6 years (range 42- 63 years), size of 7.7 cm (range 2.5-17 cm), and prior duration of 3.1 year s. Seven of eight patients had a history of prior trauma The spindled compo nent was positive for vimentin, calponin, CD34, and occasionally KP-1 or ly sozyme and negative for caldesmon, S100, and desmin. Follow-up on eight pat ients revealed four with recurrences or residual disease over three years, requiring re-excision. No cases metastasized or caused patient death (mean 12 years, range 1-23 years). We describe a predominantly fatty lesion that is hemosiderin rich with a "fibrohistiocytic" proliferation, composed of hi stiocytes, myofibroblasts, and C34-positive fibroblasts, which occurs predo minantly in the ankle region of middle-aged females. We believe that this i s a reactive process due to antecedent trauma, the inflammatory cells, hemo siderin, mixed spindled cells, and homogeneous non-neoplastic appearance of the fat. HFLL can be distinguished from previously described lesions. Corr ect identification of hemosiderotic fibrohistiocytic lipomatous lesion is i mportant, as it may locally recur.