Abstract: Objective To explore the clinicopathological features, immunophenotype, diagnosis, and differential diagnosis of nodular fasciitis(NF)in the head and neck. Methods The clinical manifestations of 28 patients with NF diagnosed pathologically in the head and neck at the Eye, Ear, Nose and Throat Hospital, Fudan University from 2008 to 2019 were collected, and their pathological morphology and immunohistochemical expression were analyzed using hematoxylin and eosin staining and EnVision. Finally, a retrospective analysis and literature review were performed. Results The number of men and women is analogous(male-to-female ratio: 1∶1.15). The age ranged from 4 to 77 years, and mean age was 40 years. The course of the disease was shorter, in the 25 patients aged less than 6 months. The average diameter of the mass was 1.3 cm, and boundary was relatively clear, 15 cases(53.6%)were located around the outer ear, face in six cases(21.4%), back of the nose and parotid gland both in three cases(10.7%), and neck in one case(3.6%). Macroscopic examination showed that tumors were mostly nodular. Microscopically, they were consisted of proliferating spindle-shaped or fat spindle-shaped fibroblasts and myofibroblasts. They were arranged in a swirling and braided pattern, and the mucus-like matrix and collagen fibers were observed. The microcystic cavity was fishnet-shaped, and extravasated red blood cells and multinucleated giant cells were often seen in the interstitial space. Immunohistochemistry expressed vimentin, SMA, MSA, calponin, and CD10 but not CK, desmin, CD34, S-100, WT-1, or ALK. During the postoperative follow-up period, which ranged from 2 to 125 months, no local replace occured. Conclusion NF is a benign, self-limiting fibroblastic/myofibroblastic proliferative lesion. Local surgical resection is the best treatment option. Because of its rapid progress, microscopic mitotic figures are easy to see and can invade surrounding tissues. It can easily be misdiagnosed as a malignant soft tissue tumor, and other tumorous lesions must be excluded before the diagnosis of NF. Subsequently, a pathological diagnosis should be made. Immunohistochemical expression results are helpful in the definitive and differential diagnoses of the disease. In addition, MYH9-USP6 gene fusion has been reported in NF^［1］. Therefore, FISH detection is feasible to help diagnose and differentiate the disease.

Key words: nodular fasciitis, clinicopathological features, immunophenotype, diagnosis, differential diagnosis