Synovial metaplasia of the skin.

Synovial metaplasia has been described in bone or soft tissues following surgical procedures or under experimental conditions. Three cases in which skin biopsies showed synovial metaplasia of the dermis are herein reported. The metaplastic foci were associated with cyst formation and transepidermal fistulae. All patients had a history of previous surgical procedures in the area, and in all, the lesions clinically resembled suture granulomas. Microscopically, the lesions bore a striking resemblance to hyperplastic synovium. The immunohistochemical studies showed strong staining with vimentin and scattered positivity with alpha-1-antichymotrypsin (alpha-1ACT) and lysozyme. No basement membrane antigens or elastic fibers were demonstrated. We believe that the name "metaplastic synovial cyst" is an appropriate pathologic designation for this entity. An increased awareness of its occurrence will help to establish its true incidence.