The origins of osteochondromas and enchondromas. A histopathologic study.

Histopathologic sections of large pieces of tissue obtained from both surgical and postmortem specimens of osteochondromas and enchondromas were analyzed to elucidate the pathogenesis of these two lesions. The osteochondroma is derived from aberrant cartilaginous epiphyseal growth plate tissue, which proliferates autonomously and separates from the normal growth plate near its edge. As growth progresses, the aberrant tissue remains in a subperiosteal location, where it may either disappear through remodeling or proliferate as an early osteochondroma perpendicular to the orientation of the growth plate from which it was derived. The enchondroma also is derived from the actively proliferating cartilaginous tissue of growth plates. For unknown reasons certain groups of chondrocytes do not proceed to undergo hypertrophy and death. As a result, a column of uncalcified cartilage extends from the underside of the growth plate into the region in which all other cartilaginous tissue has been remodeled into primary bone. The bridge to the plate may either remain intact or become interrupted by normal bone. An isolated group of chondrocytes may (1) be walled off from normal tissue by lamellar bone; (2) undergo calcification and secondary osseous remodeling, either in part or in total; or (3) proliferate as an intraosseous chondroma (benign enchondroma). A similar but not identical process of enchondroma formation may occur in fibrous dysplasia of bone, systemic growth plate dysplasias similar to achondroplasia, and osteogenesis imperfecta.