As examined by gross pathology, AMSF tumors are typically lobulated, with gelatinous, fleshy, or firm areas that vary in color and texture; they are most often localized to subcutaneous adipose tissue but may infiltrate into nearby tissues. Histopathologic microscopic examinations of hematoxylin and eosin stained tumors characteristically show spindle-shaped cells admixed with prominent inflammation-like areas containing a mixture of neutrophils, lymphocytes, and plasma cells. The areas of these lesions that contain spindle cells are often also occupied by distinctively large, variably-shaped epithelioid cells that have vesicle-laden nuclei and acidophilic (readily stained with acid dyes) nucleoli. These cells have been termed Reed-Sternberg cell-like, virocyte-like (i.e. cells which, similar to some viruses, have sticklike protrusions), and ganglion cell-like. The tumors may also contain large vacuolated pseudolipoblasts (i.e. cells that resemble lipoblasts). These various cell types are embedded in a myxoid (i.e. more blue or purple compared to normal connective tissue because of excessive uptake of the hematoxylin stain) and collagen fiber-laden tissue background. In addition to the cited cell types, the tumors may contain degenerated, dying, and or deat cells and large histiocyte-like cells that have engulfed other cells, usually neutrophils (this cell-engulfing phenomenon is termed emperipolesis). In one large study, emperipolesis of white blood cells appeared to be a helpful indicator of AMSF.) The proportions, numbers, and types of these cells varies greatly among cases and thereby may present diagnostic challenges. For example, a AMSF tumors can have dense inflammatory infiltrates which obscure other cell types and thereby suggest that the lesion is a purely inflammatory reaction. A recent immunohistochemical immunostaining small study on AMSF tumor tissue detected cells that expressed the vimentin protein in almost all cases; expressed MUC1 (also termed EMA), CD31, CD34, CD68, and PDPN proteins in a variable number of cases; and did not express CD45, CD15, CD30, HMB-45, MLANA (also termed Melan-A), desmin, GFAP, or S100 proteins. Earlier studies had reported that these cells express vimentin, periodic acid-Schiff, CD34, CD68, and S100 proteins in many cases but not MUC1, cytokeratin, or desmin proteins. The expression profiles of these proteins, which sometimes differed in different studies, have not been helpful in identifying a tumor as an AMSF.
Acral myxoinflammatory fibroblastic sarcoma
Superficial acral fibromyxoma
Peripheral ossifying fibroma
Juvenile hyaline fibromatosis
Aggressive infantile fibromatosis
Aggressive fibromatosis
Diffuse infantile fibromatosis
Juvenile active ossifying fibroma