Abstract: 【Abstract】 To report a case of cutaneous metaplastic synovial cyst. A 14-year-old male patient presented with a cystic mass on the forehead for more than 6 months. Histopathological findings revealed an intradermal cystic structure with multiple intraluminal broad band-like villiform protuberances, which was lined with a membrane resembling hyperplastic synovium and composed of a variety of cellular structures; some areas of the cystic wall were covered with fibrin-like hyaline connective tissues, and some areas were highly cellularized and lined with multiple layers of epithelioid cells and spindle cells. Immunohistochemical study revealed diffuse expression of vimentin and positive staining for the histocyte marker CD68, but negative staining for cytokeratin and smooth muscle actin in epithelioid cells and spindle cells. According to the clinical manifestations and histopathological findings, the diagnosis of cutaneous metaplastic synovial cyst was confirmed.

Key words: Synovial cyst, Metaplasia, Skin