The original idea that SCM originates from a metaplasia in the subintimal layer of the synovium, where the synovium is in direct contact with the articular cartilage, has been challenged. The high incidence of hypercellularity, binucleated cells, and cellular atypia was always an argument against a metaplastic origin for the disease. Evidence of clonal chromosomal changes, like translocation of chromosome 1218 and chromosome 5 and 6 abnormalities,19,20 in addition to other alterations,19,21 provide some evidence supporting a neoplastic rather than a metaplastic origin for SCM. Given the presence of mitosis in the present case, the lack of mitotic activity in SCM, as stated by other authors,22 is not a universal feature and cannot be used as an argument against a neoplastic origin for SCM.
Although mitotic activity is uncommon in SCM, the present case illustrates the possible presence of mitotic activity in GSSCM. The simple presence of mitotic activity, a common finding in some other chondral tumors,23,24 does not preclude the diagnosis of benign SCM, as suggested before,8 and correlation of the clinical and radiologic manifestations with histopathologic findings is crucial for a correct diagnosis.