Nodular fasciitis of the parotid gland, masquerading as pleomorphic adenoma.

It is difficult to distinguish nodular fasciitis (NF) from other neoplasm of the parotid gland, especially pleomorphic adenoma (PA) by fine needle aspiration cytology. A 39-year-old female noticed a mass in the parotid region. The aspirate material showed cohesive parts composed of the cells that had oval or spindle-shaped nuclei and relatively abundant cytoplasm and some cells with plasmacytoid features. The background substance was fibromyxoid. PA was diagnosed based on the cytologic findings. Subsequently, parotidectomy was performed and NF was diagnosed based on histologic and immunohistochemical findings. NF in the parotid region is rare and may be misdiagnosed as other benign or malignant tumors of the parotid gland. The clinical history of rapid growth and the presence of mitoses and inflammatory cells help to distinguish NF from PA. In addition, immunohistochemical stains for smooth muscle actin and CD68 are useful to confirm the diagnosis of NF.