Solitary synovial osteochondroma.

Solitary synovial osteochondroma (SSO) is a rare variant of extraskeletal osteochondroma. The aim of this study was to review 5 cases of SSO, including clinical, radiographic, and histopathologic features. Five cases of SSO were retrieved from our files. Histopathologic and radiographic findings were reviewed, and a clinicopathologic correlation was performed. Patients' ages ranged from 33 to 63 years. Knee mass was the most common presentation. All cases were well circumscribed and had multiple cartilaginous lobules surrounded by fibroadipose tissue. Microscopically, lobulated adult-type hyaline cartilage with central calcification was noted. Cytologic atypia was present in one case, but malignant features were absent. Two cases were suggestive of chondrosarcoma on imaging studies. Patients underwent surgery, which was curative in cases for which follow-up was available. In conclusion, SSO is a rare lesion that may mimic low-grade chondrosarcoma at times. Correct recognition of SSO depends on radiographic and clinicopathologic analysis.