Parotid Gland Nodular Fasciitis: A Clinicopathologic Series of 12 Cases with a Review of 18 Cases from the Literature.

Nodular fasciitis (NF), very uncommon in the parotid gland, is a benign myofibroblastic proliferation that may be mistaken for other neoplastic proliferations. The mass-like clinical presentation and histologic features result in frequent misclassification, resulting in inappropriate clinical management. There are only a few reported cases in the English literature. Cases within the files of the authors' institutions (retrospective) confined to the parotid gland were compared to cases reported in the English literature (Medline 1966-2014). The patients included five females and seven males, aged 11-70 years (mean 45.2 years). All patients presented with a mass lesion, present on average 1.9 months, without a documented history of trauma. The lesions were 0.7-5.2 cm (mean 2.2 cm). Seven patients had fine needle aspiration. The majority of the lesions were circumscribed (n = 9), composed of spindle-shaped to stellate myofibroblasts (MF) arranged in a storiform growth pattern, juxtaposed to hypocellular myxoid tissue-culture-like areas with extravasation of erythrocytes. Dense, keloid-like collagen (n = 7) and occasional giant cells were seen (n = 6). Mitotic figures (without atypical forms) were readily identifiable (mean 4/10 HPFs). By immunohistochemical staining, the MF were reactive with vimentin, actins, and calponin, while the histiocytes were reactive with CD68. All patients had surgical excision. One patient developed local recurrence (12 months later). All were alive and disease free at last follow-up, with a mean 133 months of follow-up. The principle differential diagnoses include fibrosarcoma, fibromatosis, pleomorphic adenoma, myoepithelioma, neurofibroma, schwannoma, solitary fibrous tumor, leiomyoma, fibrous histiocytoma and myxoma. NF of the parotid gland occurs in middle-aged patients who present with a mass (mean 2.2 cm) in the parotid gland of short duration (1.9 months). FNA misinterpretation frequently leads to excision. Separation from myoepithelial and mesenchymal lesions affecting the parotid gland results in appropriate management.