Fasciitis nodularis pseudosarcomatosa M72.41

Benign, rapidly growing subcutaneous tumor of unknown genesis originating from the fascia with a tendency to spontaneous regression, histologically reminiscent of a fibrosarcoma.

Unclear; traumas? Molecular biology revealed a MYH9/USP6 fusion gene. This is probably a defect that promotes a reactive inflammatory process (Wil M et al. 2018).

Solitary, usually not > 2.0 cm, maximum up to 3.0 cm in size, subcutaneous, coarse, usually asymptomatic, often caked to the underlying tissue, easily delimited, rapidly growing, sometimes painful under pressure . Spontaneous regression has been observed in individual cases. S.a.u. Fasciitis ossificans; see also cranial fasciitis of childhood.

Connective tissue tumor originating in the fascial tissue and growing into the subcutaneous fatty tissue, rarely also into the musculature, which is rich in vessels and consists mainly of large, spindle-shaped fibroblasts and myofibroblasts with numerous mitoses. Few vascular incisions, partly with prominent endothelia. In varying density multinucleated giant cells, partly with bizarre nuclear formations. Underlaid is a loose myxoid stroma, which has a diagnostically significant fibrous structure.

Immunohistology: spindle cells = vimentin pos., muscle actin (HHF35 and alpha-SMA pos.); giant cells = S100 pos., muscle actin pos.

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