A 30-Year-Old Man With a Soft Tissue Mass on the Right Elbow

A 30-year-old previously healthy man presented with a painless soft tissue mass on his right elbow. Macroscopic examination revealed a firm, tan-white multilobulated tissue measuring 2.8 × 2.2 × 1.4 cm, attached to a small amount of fibroadipose tissue.Light microscopic examination of hematoxylin-eosin– stained sections showed a tumor with a vaguely multinodular configuration. The tumor had a background of myxoid and hyaline areas with dense inflammatory infiltrate consisting of lymphocytes, plasma cells, and neutrophils with prominent eosinophilic infiltrate (Figure 1).High-power examination of the cellular areas revealed bizarre atypical cells deposited in a hyalinized and myxoid stroma. Some of these atypical cells were large epithelioid cells with abundant basophilic cytoplasm, large vesicular nuclei, and macronucleoli. These cells were similar to virocytes or Reed-Sternberg cells (Figure 2). Others were multivacuolated cells of varying size, bearing a close resemblance to pleomorphic lipoblasts (Figure 3). Multiple giant cells were seen, the cytoplasm of which was packed mainly by neutrophilic and eosinophilic leukocytes (Figure 4). No mitotic activity was noted.Immunohistochemically, the tumor cells were diffusely positive for vimentin. CD68 staining was positive in a few scattered multivacuolated cells. All other markers, including keratin CAM 5.2, keratin AE1:AE3, epithelial membrane antigen, S100 protein, HMB-45, Melan-A, smooth muscle actin, desmin, factor VIII, CD15, CD30, and CD34, were negative.What is your diagnosis?We report a case of inflammatory myxohyaline tumor (IMT) of the distal extremities occurring in a 30-year-old man who presented with a painless mass on his right elbow. Histologic examination of the tumor showed an intense acute and chronic inflammation, with prominent eosinophilic infiltrate in a myxohyaline background. There were 3 main types of tumor cells seen. The first type was similar to virocytes or Reed-Sternberg cells, the second type was multivacuolated cells mimicking pleomorphic lipoblasts, and the third type was giant cells with features of emperipolesis. Immunohistochemically, the tumor cells were diffusely positive for vimentin, with a few scattered cells being positive for CD68. Inflammatory myxohyaline tumor of the distal extremities is a low-grade malignant tumor with high risk for local recurrence. Distant metastases are unusual.Inflammatory myxohyaline tumor (IMT) of the distal extremities is also known as inflammatory myxohyaline tumor of the distal extremities with virocyte or Reed-Sternberg–like cells,1 acral myxoinflammatory fibroblastic sarcoma,2 and inflammatory myxoid tumor of the soft parts with bizarre giant cells.3 It was first described by Montgomery et al in 1997.4 It was often mistaken for an inflammatory or infectious process, Hodgkin disease, or various sarcomas.1It is rare to see IMT of the distal extremities, and it occurs primarily in adults, with a peak incidence in the fourth and fifth decades of life. Men and women are affected equally. Most patients present with a slowly growing, painless, ill-defined mass of the distal extremities. Grossly, the tumor is typically multinodular and poorly circumscribed and is often removed piecemeal by the surgeon. Gelatinous-appearing areas are conspicuous in the lesions, with extensive myxoid change. The tumor ranges in size from 1 to 8 cm (mean, 3–4 cm). Microscopically, the tumor has a myxoid background with marked inflammatory reaction consisting of neutrophils, plasma cells, lymphocytes, and eosinophils. The inflammatory cells are admixed in a rich vascular network resembling nonspecific granulation tissue. Three main types of neoplastic cells are usually seen in this tumor. The first type of cells is characterized by large polygonal ganglion-like cells with basophilic cytoplasm, an oval nucleus with vesicular chromatin, and a huge prominent nucleolus. They are similar to Reed-Sternberg cells, which are seen in the mixed cellularity type of Hodgkin disease. The second type comprises multivacuolated cells of varying size mimicking pleomorphic lipoblasts. The third type of cells seen in IMT is characterized by the presence of giant cells in which the cytoplasm is packed mainly by neutrophils, lymphocytes, and eosinophils. It may also contain plasma cells and red blood cells, consistent with emperipolesis. Mitotic activity usually does not exceed 1 in 10 cells per high-power field, without atypical mitotic figures. Necrosis is rarely seen.5Immunohistochemically, the tumor cells are diffusely positive for vimentin, with a few scattered multivacuolated cells being positive for CD68. All other markers, including keratin CAM 5.2, keratin AE1:AE3, epithelial membrane antigen, S100 protein, HMB-45, Melan-A, smooth muscle actin, desmin, factor VIII, CD15, CD30, and CD34, are negative.5It is important to distinguish IMT from other myxoid tumors of soft tissue as myxoid variants of malignant fibrous histocytoma and pleomorphic liposarcoma. They differ from IMT by their much higher mitotic rate, with frequent atypical mitoses. No marked inflammatory reaction or emperipolesis is seen. Pleomorphic liposarcoma and the myxoid variant of malignant fibrous histiocytoma are rare in the soft tissues of the hands and fingers. Rosai-Dorfman disease is included in the differential diagnosis, as it is characterized by emperipolesis, without intranuclear and cytoplasmic vacuoles. Immunohistochemically, the tumor cells in Rosai-Dorfman disease are positive for S100.3 Ultrastructurally, the IMT tumor cells have features of modified fibroblasts, including an abundance of intermediate filaments and dilated rough endoplasmic reticulum.2 The only case study in which cytogenetic information is included showed t(1;10) and loss of chromosomes 3 and 13.6 Inflammatory myxohyaline tumor has a high propensity for local recurrence. Only one case with metastases to the regional lymph nodes is documented.2 Metastases to distant lymph nodes and lung occur but are rare (<2% of all reported cases).2In summary, awareness of this entity is important to avoid misdiagnosing this IMT as an inflammatory process, Hodgkin disease, or various types of sarcomas. Helpful diagnostic features are the presence of mixed inflammatory cells in a myxohyaline background, with 3 main types of tumor cells. The first type is similar to virocytes or Reed-Sternberg cells, the second type is multivacuolated cells mimicking pleomorphic lipoblasts, and the third type is giant cells with features of emperipolesis. In our case report, the histologic features of IMT support the overall diagnosis, with prominent eosinophilic infiltrate as a unique feature.

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