A new histologic approach to the differentiation of enchondroma and chondrosarcoma of the bones. A clinicopathologic analysis of 51 cases.

Fifty-one cases of central, hyalin cartilage tumors of the long and flat bones were analyzed. Although Grade 2 and 3 chondrosarcomas could be diagnosed on the basis of cytologic features alone, low-grade chondrosarcoma could not be adequately differentiated from pure, benign enchondroma(s) by cytology alone. The tumors can be distinguished by a new histologic approach based on tissue patterns. The crucial enchondroma patterns consist of multiple nodules of hyalin cartilage separated by normal marrow in conjunction with partial to complete encompassing plates of lamellar bone that conform to the irregular shapes of the cartilage nodules. The chondrosarcomatous patterns consist of a single confluent mass of cartilage, which commonly permeates the marrow, "trapping" host lamellar bone on all sides, and which forms bands of fibrosis between the confluent peripheral cartilage lobules. Other less common patterns included cartilagenous infiltration of the Haversian systems or marrow fat and/or the development of a soft tissue mass. A central secondary chondrosarcoma is defined as one that shows the combination of both the enchondromatous and chondrosarcomatous patterns. All 18 of the pure enchondromas diagnosed by the methods proposed in this article behaved with strict benignity (i.e., without evidence of recurrence or metastasis with an average follow-up period of 7.2 years). The 33 primary and secondary chondrosarcomas diagnosed using the described patterns behaved with the predicted frequency of recurrence, metastasis, and patient demise.