Fibrous Histiocytoma

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Clinical Features

    Densely fibrous mucosal mass is poorly 
demarcated from the underlying connective tissue.






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Fibrous histiocytoma represents a benign but diverse group of neoplasms which exhibit both fibroblastic and histiocytic differentiation. The cell of origin is believed to be the histiocyte, but the varied microscope appearances of the lesion has led to the use of numerous alternative diagnostic terms, including dermatofibroma, sclerosing hemangioma, xanthogranuloma, fibroxanthoma, and nodular subepidermal fibrosis. A malignant variant of this neoplasm is discussed in the following section.

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Clinical Features

The most common location of fibrous histiocytoma occurrence is the skin of the extremities, where it usually presents as a small, firm nodule. Oral and perioral lesions are uncommon, but when seen they occur predominantly on the buccal mucosa and vestibule. The oral lesion is typically found in middle-aged and older adults, where it presents as a painless submucosal nodule which can vary in size from a few millimeters to several centimeters. Deeper tumors tend to be larger and most lesions cannot be easily moved about beneath the epithelium.

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Pathology and Differential Diagnosis

Fibrous histiocytoma is characterized by a submucosal, cellular aggregation of spindle-shaped, fibroblast-like cells with relatively pale, oval nuclei; scattered rounded histiocytic cells are also present. Foamy histiocytes and Touton-type multinucleated giant cells, with nuclei pushed to the periphery, may be seen to contain phagocytosed lipid or hemosiderin; these cells sometimes are so numerous that they form xanthomatous aggregates. A background stoma of variably dense collagenic tissue and vascularity is seen. The spindled cells may be arranged randomly but usually there are large areas with tumor cells streaming in interlacing fascicles from a central nidus and intersecting with cells from adjacent aggregates, imparting a storiform or crisscross pattern on low power magnification (Figure 6).

The fibrous histiocytoma is poorly demarcated from surrounding tissues and is separated from the overlying mucosa by a zone of fibrovascular connective tissue (grenz zone). The overlying epithelium often demonstrates considerable acanthosis, with regular elongation of rete processes. Chronic inflammatory cells, especially lymphocytes, are usually scattered throughout the tumor in small numbers. The lesional stroma is occasionally very densely fibrotic or hyalinized, leading some in the past to use the diagnostic misnomer sclerosing hemangioma. Deeper lesions may contain focal areas of dystrophic calcification or metaplastic osteoid.

Acid phosphatase, nonspecific esterase and succinate dehydrogenase enzymes are consistently present in lesional cells, especially those resembling rounded histiocytes. A significant proportion of cases will be immunoreactive for alpha-1-antitrypsin and factor XIIIa antigen. CD68, a macrophage antigen, usually does not mark the tumor cells. Electron microscopy has shown a spectrum of cell types from spindled fibroblastic cells to rounded histiocyte-like cells; endothelial lesional cells are not seen.

When the lesion is comprised predominantly of proliferating sheets of histiocytes with few Touton giant cells and foamy cytoplasm, the terms xanthogranuloma or juvenile xanthogranuloma have traditionally been applied. These are typically better circumscribed and less fibrosed than the more routine fibrous histiocytoma. This lesion is usually diagnosed during the first two decades of life and must be differentiated from soft tissue lesions of Langerhans cell disease (histiocytosis X) and from routine xanthoma, or reactive histiocyte proliferations as seen after trauma, or in persons with hyperlipidemia or hypercholesterolemia. The histiocytic cells of a xanthoma typically express S-100 protein, while the lesional cells of the fibrous histiocytoma do not. Cholesterol clefts, moreover, are commonly seen in the xanthoma. The multinucleated giant cells of Langerhans disease do not typically have their nuclei pushed to the cell periphery.

Benign fibrous histiocytoma is often confused with other benign fibrous lesions and must be differentiated from nodular fasciitis, myofibroma, palisading encapsulated neuroma, neurofibroma, leiomyoma and the spindle cell type of myoepithelioma. It is important, moreover, to separate this tumor from aggressive forms of fibrous and fibrohistiocytic neoplasms such as dermatofibrosarcoma protuberans, malignant fibrous histiocytoma and fibrosarcoma.

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Treatment and Prognosis

Benign fibrous histiocytoma is treated by wide surgical excision, with 5-10% of cases recurring locally. Deeper and larger lesions have a higher rate of recurrence. More aggressive examples usually show the microscopic features of dysplasia, such as marked cellularity, mitotic activity, focal necrosis, even atypical giant cells. It is sometimes, however, very difficult to predict biological behavior on the basis of cellular features, as illustrated by the occasional case which metastasizes despite its bland histopathologic appearance. For this reason extended follow-up is recommended after surgical removal.

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References (Chronologic Order)

Note: General references can be found by clicking on that topic to the left.

Hoffman S, Martinez MG Jr. Fibrous histiocytomas of the oral mucosa. Oral Surg Oral Med Oral Pathol 1981; 52:277-283.

Gonzalez S, Duarte I. Benign fibrous histiocytoma of the skin: a morphologic study of 290 cases. Pathol Res Pract 1982; 174:379-391.

Thompson SH, Shear M. Fibrous histiocytomas of the oral and maxillofacial regions. J Oral Pathol 1984; 13:282-294.

Fletcher CD. Benign fibrous histiocytoma of subcutaneous and deep soft tissue: a clinicopathologic analysis of 21 cases. Am J Surg Pathol 1990; 14:801-809.

Gray PB, Miller AS, Loftus MJ. Benign fibrous histiocytoma of the oral/perioral regions: report of a case and review of 17 additional cases. J Oral Maxillofac Surg 1992; 50:1239-1242.

Bielamowicz S, Dauer MS, Chang B, Zimmerman MC. Noncutaneous benign fibrous histiocytoma of the head and neck. Otolaryngol Head Neck Surg 1995; 113:140-146.

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