Low-grade, aggressive fibrous histiocytoma of the medial canthus

Abstract

Fibrous histiocytoma (FH) encompasses a heterogeneous group of mesenchymal tumours composed of varying proportions of fibroblastic and histiocytic elements. Here we describe the rare occurrence of FH in the medial canthus. A 26-year-old woman presented with a 5-month history of an enlarging, mildly tender, yellowish mass in the left medial canthal area (Fig. 1A). Clinically, the appearance was consistent with a noninflamed, cystic lesion, and a diagnosis of epidermal inclusion cyst was favored. Excisional biopsy revealed spindle cells occasionally in a storiform arrangement (Fig. 1B), focal vacuolated histiocytes, rare multinucleated giant cells, and prominent peripheral sclerotic collagen bundles. There was no overlying epidermis or capsule. These findings were in keeping with a benign fibrosing process. Six months later, the patient presented with a recurrent mass requiring a second biopsy. This specimen had similar features but, additionally, showed a hyperplastic epidermis and 3–4 atypical mitoses in 20 high-power fields. Immunohistochemical staining was positive for smooth-muscle actin, muscle-specific actin, vimentin, and CD68. Staining for CD34, desmin, S-100, and HMB45 was negative. The diagnosis was low-grade aggressive FH of the medial canthus. There has been no further recurrence after 46 months. FH, believed to be derived from a pluripotential primitive mesenchymal cell, has been described in the orbit, eyelids, conjunctiva, episclera, limbus, cornea, and lacrimal sac. In a review of 150 cases of orbital FH, Font and Hidayat1 distinguished 3 groups: benign, locally aggressive, and malignant. Epithelioid and cellular variants of benign FH have been reported in the medial canthus.2 Four cases of canthal malignant FH have also been reported together with a review of the differential diagnosis.3 The major differential diagnosis of benign or aggressive FH in the canthal region is nodular fasciitis. Histologic and immunohistochemical findings, as demonstrated in our case, can be helpful in diagnosis; however, many overlapping features can make this distinction difficult. Some nodular fasciitis lesions show a storiform pattern, and the amount of myxoid matrix can be minimal.4 Transitional forms can make the distinction between FH and nodular fasciitis particularly difficult, if not impossible in some cases.4