Intraarticular nodular fasciitis--a rare lesion: clinicopathologic analysis of a series.

Nodular fasciitis is a benign myofibroblastic proliferation with a predilection for the subcutaneous tissues of the upper extremities, trunk, and head and neck of young adults. Nodular fasciitis is not generally recognized to arise within joints. In this study, the clinicopathologic and immunohistochemical features of 10 cases of intraarticular nodular fasciitis are described. Six patients were female and 4 were male, with a median age of 33 years (range, 9-50 years). Lesional size ranged from 2 to 4 cm (median, 2.6 cm). Seven tumors arose in the knee, 2 in the hand, and 1 in the ankle. Most patients complained of joint pain; 4 presented with a palpable mass. Only 1 patient reported antecedent trauma. The duration of symptoms prior to surgery ranged from 2 months to 1 year (median, 6 months). The clinical differential diagnoses included giant cell tumor of tendon sheath, pigmented villonodular synovitis, synovial chondromatosis, inflammatory arthritis, and lymphoma. Grossly, the lesions were solid, nodular, rubbery, or firm masses. Histologically, all tumors were circumscribed but unencapsulated and showed typical features of nodular fasciitis, being composed of cytologically bland plump spindle cells arranged in short, intersecting bundles within a variably loose myxoid to collagenous stroma, containing extravasated red blood cells and scattered lymphocytes. Five lesions showed prominent stromal hyalinization, in 2 cases keloidal in appearance. In 4 cases, the tissue at the periphery of the lesion showed hemosiderin deposition. By immunohistochemistry, all tumors examined were positive for SMA, 1 was positive for desmin, and all were negative for caldesmon and S-100 protein; none showed nuclear staining for beta-catenin. Clinical follow-up information was available for 5 patients, ranging from 2 to 86 months. No lesion recurred. In summary, intraarticular nodular fasciitis occurs most commonly in the knees of young adults, and often appears to have a somewhat longer preoperative duration than typical subcutaneous or intramuscular nodular fasciitis. Intraarticular lesions show morphologic features similar to other cases of nodular fasciitis, with the exception that stromal hyalinization and adjacent hemosiderin deposition are common, likely attributable to frictional trauma in this location.