[Intramuscular nodular fasciitis--a clinicopathological study with emphasis on myogenic giant cells].

Nodular fasciitis is a frequently occurring pseudosarcomatous fibrous proliferation which usually affects the subcutaneous tissue. In the present study, we investigated tissue specimens from 26 patients with intramuscular nodular fasciitis. The median age of patients was 31 years, with the tumors occurring mainly in the extremities (11 patients) and the trunk (11 patients). These had an average size of 2.6 cm. Males predominated (male:female 9:4). Histological examination revealed a proliferation of myofibroblasts (positive for smooth muscle-actin) embedded in a myxoid or fibrous stroma. In 25/26 cases, myogenic giant cells were observed (positive for desmin, negative for smooth-muscle actin and CD 68). Less frequently (11/26 patients), osteoclastic giant cells were found (positive for CD 68, negative for desmin and smooth-muscle actin). In intramuscular nodular fasciitis, myogenic giant cells are encountered more often than previously described. They are relevant for the differential diagnosis of sarcoma and fibromatoses, since they can be misinterpreted as neoplastic giant cells. However, the uniformity of the myofibroblastic proliferate and the myogenic phenotype of the giant cells without proliferative activity (no mitoses, negativity for Ki-67) lead to a correct diagnosis.