Nodular fasciitis: diagnosis by fine needle aspiration biopsy

OBJECTIVE: To describe the cytomorphologic features of nodular fasciitis that differentiate it from schwannoma. STUDY DESIGN: The cytomorphologic features of 10 cases of nodular fasciitis were compared to those of 4 cases of biopsy-proven schwannoma. Aspirate smears were evaluated for cellular cohesion, cell type and stroma. Immunoperoxidase stains were utilized in select cases. RESULTS: The cases of nodular fasciitis exhibited cohesive clusters of epithelioid to spindle-shaped cells in a background of single, intact mesenchymal cells; inflammatory cells; and myxoid stroma. In contrast, schwannomas lacked single, intact cells and inflammation. Schwannoma stroma was also myxoid but appeared more finely fibrillar, and cell clusters were notable for alternating areas of hypercellularity and hypocellularity. Immunoperoxidase stains demonstrated smooth muscle actin reactivity in 5 cases of nodular fasciitis and S-100 in 2 cases of schwannoma. CONCLUSION: Nodular fasciitis can be distinguished from schwannomas on the basis of cytomorphologic features and immunocytochemical profile. Cytologic diagnosis of nodular fasciitis is important since it obviates the need for surgical excision.