Nodular fasciitis is a reactive lesion and is most commonly mis-diagnosed as a neoplastic tumor.
These lesions do not recur after excision.
Nodular fasciitis often occurs in young and middle age adults with an equal frequency in males and females.
Usually, there is a history of rapid growth in extremities.
Grossly, the lesion appears as a nodule.
Microscopically, early lesions consist of short bundles of spindle fibroblasts and myofibroblasts in a loose myxoid stroma. Some cells have large nuclei and nucleoli and may exhibit mitosis, however, the mitotic figures are not atypical. As the lesion matures, the periphery becomes more cellular showing a haphazard, closlely packed and somtimes a vaguely stroiform fibroblastic proliferation. Some mononuclear inflammatory cells and red blood cells are also present and occasionally, lipid-laden histiocytes, benign appearing giant cells, foci of cartilage and osteoid and atypical ganlion-like cells are seen. In the end stage lesion, thick bundles of collagen have replaced most fibroblasts. The lesion shows permeation of adjacent structures such as muscle, therefore, the lesion has indistinct borders and may show presence of entrapped muscle fibers.