Nodular fasciitis has been generally considered as a benign and probably reactive fibroblastic growth originating from the subcutaneous fascia. In the present paper, we report a case with nodular fasciitis arising in the retroauricular region. The patient was a 23-year-old woman who had noticed a mass about 5 mm in diameter in the left retroauricular region. She was referred to our hospital because the mass was gradually growing and was tender to touch. At the initial examination, a pigmented mass about 1 cm in size was found in the left retroauricular region. The surface was smooth and the mass was freely mobile. Computed tomography (CT) revealed a mass-like tension which showed the same enhancement as a venous intensity. At operation, we found a white solid mass which had no capsule. The mass was easily removed, because it was not adherent to the surrounding tissues. The pathological diagnosis was nodular fasciitis which showed positive immunostaining for vimentin, HHF 35 (muscle actin), type III collagen and lysozyme, but negative immunostaining for desmin, S-100 protein and CD 34. This rare condition can be diagnosed only by pathological examination, however, it must be kept in mind in the differential diagnosis of retroauricular mass lesions.
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