A 29-year-old man presented with gradually increasing swelling over the proximal left little finger. There was no history of trauma. The patient had several cats at home and was concerned about the possibility of cat-scratch disease. Initial radiographs showed a soft tissue shadow but no bony changes. Subsequent radiographs obtained at the time of orthopedic oncology consultation showed an increase in the size of the soft tissue mass accompanied by bony erosion but no periosteal reaction. Magnetic resonance imaging showed a heterogeneous mass nearly completely encircling the underlying proximal phalanx.
Core needle biopsy of the mass showed a variably cellular, vaguely nodular neoplasm composed of inflammatory, myxoid, and hyalinized areas. The inflammatory zones contained large atypical epithelioid cells surrounded by lymphocytes, plasma cells, and sheets of eosinophils (Figure 1). Many of the large atypical cells showed large vesicular unilobed or bilobed nuclei, prominent eosinophilic macronucleoli, and abundant cytoplasm, thus resembling Reed-Sternberg cells (Figure 2). The myxoid areas showed cords of cells reminiscent of extraskeletal myxoid chondrosarcoma, alternating with areas showing lipoblast-like cells (Figure 3). Mitoses were rare. The atypical cells were negative for S100, CD1a, CD15, and CD30. Because of the rarity of the lesion, it was sent to an outside expert in soft tissue pathology, who concurred with our diagnosis.
The patient underwent ray resection of the finger. The specimen showed a bulbous protuberance of the middle interphalangeal joint. Sectioning revealed a 3-cm, gray-white tumor (Figure 4) involving the subcutaneous tissue, skeletal muscle, and superficial portions of the underlying bone. There was focal hemorrhage, but no necrosis. Microscopic sections showed an appearance identical to the biopsy specimen.
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Pathologic Diagnosis: Myxoinflammatory Fibroblastic Sarcoma
Abstract
A 29-year-old male patient presented with a slowly growing mass in his left little finger. Radiologic studies showed a soft tissue mass around the middle interphalangeal joint. Trucut biopsy of the mass and a subsequent resection showed a neoplasm composed of inflammatory, myxoid, and hyalinized areas. Large atypical epithelioid cells with macronucleoli and abundant cytoplasm were seen against a background of lymphocytes, plasma cells, and sheets of eosinophils. The myxoid areas showed cords of cells in a loose background alternating with areas showing lipoblast-like cells. The variegated light microscopic appearance, coupled with the cytologic features of the atypical epithelioid cells, is key to the diagnosis of myxoinflammatory fibroblastic sarcoma. This entity must be considered whenever a myxoid or inflammatory mesenchymal lesion is encountered in the distal extremities.
Myxoinflammatory fibroblastic sarcoma (MIFS) was first described by Montgomery et al1 in 1998 as “inflammatory myxohyaline tumor of the distal extremities with virocyte or Reed-Sternberg like cells” and later in the same year by Meis-Kindblom and Kindblom2 as “acral myxoinflammatory fibroblastic sarcoma.” A total of 121 cases have been reported in the literature to date (December 2004), 95 of them from the 2 initial series.1–9 Myxoinflammatory fibroblastic sarcoma is currently included in the World Health Organization classification of tumors of soft tissue under the heading of fibroblastic/myofibroblastic tumors.
Myxoinflammatory fibroblastic sarcoma generally presents as a soft tissue mass of the distal extremities (hands or feet), although it has also been reported in the proximal soft tissues of the limbs.1,5 Most patients are adults, with a peak in the fourth and fifth decades of life, but patients in reported cases have ranged in age from 4 to 91 years.1,2 Male and female patients are equally affected. The most common presentation is a slowly growing painless mass in the hands or feet.
Gross examination usually reveals a multinodular tumor with myxoid areas. Histologically, MIFS shows variable nodularity and is characterized by a striking admixture of inflammatory, myxoid, and hyalinized areas. The inflammatory areas show sheets of eosinophils, lymphoid aggregates, and plasma cells with admixed large, bizarre, ganglion-like cells. The ganglion-like cells are uni- or multinucleate with a prominent eosinophilic macronucleolus, distinctly resembling Reed-Sternberg (“virocyte-like”) cells. The myxoid and hyalinized areas vary in proportion, the former showing cords of epithelioid, stellate, or vacuolated lipoblast-like cells in a myxoid matrix. The lipoblast-like cells have a hyperchromatic nucleus pushed to one side by 1 or more large vacuoles, which stain positively for mucin. Mitotic figures are rare. Immunohistochemically, the tumor cells show strong positivity for vimentin and variable expression of CD68 and CD34. They are negative for leukocyte common antigen, T- and B-cell markers, CD15, CD30, and keratins.
The differential diagnosis of MIFS1,2,7 includes benign entities such as nodular fascitis, tenosynovial giant cell tumor, inflammatory myofibroblastic tumor, and infectious lesions. Although these tumors may focally resemble MIFS, they lack the atypical virocyte-like cells that are characteristic of this tumor. Malignant tumors that may resemble MIFS are myxoid malignant fibrous histiocytoma, myxoid liposarcoma, leiomyosarcoma, inflammatory fibrosarcoma, and epithelioid sarcoma. These lesions rarely occur in the hands and feet, whereas such a location is characteristic of MIFS. The presence of foci of high-grade pleomorphic storiform sarcoma and a predominantly myxoid matrix favors a diagnosis of myxoid malignant fibrous histiocytoma over MIFS, whereas the presence of large areas of inflammation and virocyte-like cells should suggest the latter diagnosis. Myxoid liposarcoma usually occurs in deeper soft tissues and lacks an inflammatory background. Further, the vacuoles seen in true lipoblasts contain fat rather than mucin, as seen in MIFS. Necrosis or immunoreactivity for keratin should suggest epithelioid sarcoma, whereas desmoplasia or inflammation favors MIFS over epithelioid sarcoma.
References
The authors have no relevant financial interest in the products or companies described in this article.
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