Clinicopathologic conferenceA giant radiopaque mass in the masticatory space

A 2-year-old boy presented with a giant mass in the masticatory space. The mass exhibited a lobulating ossification, with no attachment to the adjacent normal bone. An enucleation was performed under the tentative diagnosis of extra-articular synovial chondromatosis, benign ossifying neoplasm, non-neoplastic heterotopic ossification, or low-grade malignancy. Upon microscopic examination, the excised mass was composed of multiple osteocartilaginous areas. We hereby present detailed clinicopathological findings.