Nodular fasciitis of the parotid gland, masquerading as pleomorphic adenoma

Abstract

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.

Keywords: Adenoma, pleomorphic; Nodular fasciitis; Parotid gland.

Fig. 1.

Computed tomography image and gross finding of the parotid mass. (A) Computed tomography scan shows a 1.9×1.3×1.2-cm-sized, heterogeneously enhancing lobulated mass (*). (B) The excised tumor is relatively well demarcated, but not encapsulated. The cut surface of the mass is solid and gray white.

Fig. 2.

The cytologic findings of the parotid mass. (A) On low power, the aspirate shows moderately increased cellular areas and rather fibrous stroma. (B) The cells in the loose fibrocellular part have oval or spindle-shaped nuclei with abundant cytoplasm and are arranged in short loose bundles with myxoid background. (C) Some cells seem to have plasmacytoid features and many inflammatory cells are present (arrows). One mitotic cell is also found (*). (D) The cells in some areas consist of tight fascicles (A–D, Papanicolaou stain).

Fig. 3.

The histologic and immunohistochemical findings of the parotid mass. (A) The tumor is composed of relatively uniform spindle-shaped cells arranged in short fascicles. (B) The stroma focally shows loose myxoid features and diffusely scattered extravasated erythrocytes are also noted. (C) A mitotic cell (*) is present. The spindle cells are positive for alpha-smooth muscle actin (D), and negative for S-100 (E). (F) Ki-67 nuclear labeling cells are mildly increased.