INTRODUCTION Nodular fasciitis is a benign reactive proliferation of fibroblasts in the subcutaneous tissues.
It is also referred to as subcutaneous pseudosarcomatous fibromatosis or proliferative fasciitis. It is seen most commonly in young individuals between 30 and 40 years of age, with about 10% occurring in children. The cause is unknown, but in some cases there may be a history of trauma. It is believed that they may be triggered by a local injury or inflammatory process. Because of the rich cellularity, mitotic activity, and rapid growth these lesions are often misdiagnosed as a sarcoma. Occasionally metaplastic bone formation may occur within the lesion in which case they may be referred to as ossifying fasciitis.
CLINICAL PRESENTATION Nodular fasciitis presents as a small rapidly growing, solitary, grey to white solid lesion in the subcutaneous tissue that may be flat or slightly elevated. In about one-third of cases there may be associated pain or tenderness. Rarely, they may arise in Tenon's capsule or conjunctiva, or in the deep orbit.
HISTOPATHOLOGY Nodular fasciitis is characterized by a proliferation of spindle-shaped to plump fibrob-lasts that tend to be haphazardly arranged. A vague storiform (cartwheel) pattern is sometimes present focally. Mitoses are frequent, but atypical mitotic figures are rare. Cleft-like spaces between fibroblasts may be seen (shown below). Capillaries within the lesion commonly have plump endothelial cells. The tumors are very cellular and collagen is typically sparse. Lymphocytes are scattered throughout the tumor, though they are not abundant.
DIFFERENTIAL DIAGNOSIS The differential diagnosis includes benign tumors such as fibrous histiocytoma, epidermal hyperplasia, neurofibroma, and spindle cell lipoma. They can also be mistaken for malignant lesions including leiomyosarcoma, fibrosarcoma, and malignant peripheral nerve sheath tumors.
TREATMENT Treatment is not necessary since these are benign with no potential for metastatic spread.
However, because of their rapid initial growth, biopsy or excision is usually performed. Spontaneous resolution has been reported, and intralesional steroid injection has been reported to result in rapid regression.
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