Diagnostic Considerations
Enchondroma
In middle-aged or elderly patients, enchondroma should be differentiated from low-grade chondrosarcoma. Clinical distinctions can be made on the basis of pain, and radiologic distinctions are based on preservation of cancellous bone or adjacent cortex. In terms of histologic features, chondromas lack cellular atypia. In enchondroma, the cartilage cell nuclei are small and uniform. A homogenous chromatin is present, and multinucleated chondrocytes are infrequent. The cartilage matrix is well formed, without prominent myxoid features.
Another condition to be considered in the differential diagnosis is chondroid differentiation in fibrous dysplasia. During histologic examination, the presence of fibro-osseous elements adjacent to cartilaginous nodules and the radiologic finding of diaphyseal localization and a ground-glass appearance favor the diagnosis of fibrous dysplasia.
Bone islands and bone infarcts can mimic enchondroma. Bone islands are densely sclerotic and appear as bone within bone because of the presence of cortical bone in cancellous bone. As seen under a microscope, bone islands are composed of compact lamellar bone.
Bone infarcts commonly occur in the metaphysis of long bones around the knee. Epiphyseal involvement may be described as avascular necrosis. On radiographs, bone infarcts appear as irregular, sharply demarcated intramedullary opacities at the metaphysis or the metaphyseal-diaphyseal area. They are composed of irregular fragments of necrotic bone trabeculae, with intervening hyalinized fibrous tissue and fat necrosis. The amount of dystrophic calcification varies.
Periosteal (juxtacortical) chondroma
Juxtacortical chondrosarcoma may appear similar to periosteal chondroma. However, juxtacortical chondrosarcomas are usually large (>5 cm), and they do not have the buttressing of solid periosteal new bone at the margins (this lack is a characteristic feature of these lesions).
Periosteal osteosarcoma is a predominantly cartilaginous form of a surface osteosarcoma that may have the Codman triangle at its upper limits. However, periosteal osteosarcoma also lacks the buttressing of solid periosteal new bone at the margins. In periosteal chondroma, there may be excavation of the underlying cortex, but it is not associated with complete cortical disruption. Furthermore, the lesion in periosteal chondroma is clearly demarcated from the medullary cavity by a continuous rim of cortical bone.
Ollier disease and Maffucci syndrome
Ollier disease is a nonhereditary skeletal disorder involving multiple enchondromas, typically metaphyseal. It commonly affects the appendicular skeleton, but the axial skeleton is not exempt. The cartilage of Ollier disease, unlike that of solitary enchondromas, has a propensity for continuous slow growth. Patients require lifelong surveillance because of a risk of secondary sarcomatous change. In some cases, surgery is indicated to correct deformity or limb-length discrepancy. In extreme cases, amputation may be needed to address stunted growth.
Maffucci syndrome consists of multiple enchondromatosis (like Ollier disease), with extraskeletal soft-tissue angiomatosis involving the skin, soft tissues, and visceral organs (including the lungs and liver). The soft-tissue angiomas are typically cavernous angiomas with frequent thrombosis and calcified thrombi.
The concern with Ollier disease and Maffucci syndrome is the incidence of secondary chondrosarcoma. Although the risk is hard to estimate for a single lesion, about 10-30% of patients with Ollier disease develop secondary chondrosarcomas. With Maffucci syndrome, at least one of the enchondromas may undergo malignant transformation at some point in the patient's lifetime.
Soft-tissue (synovial) chondroma
Soft-tissue chondromas are chondromas that arise from tenosynovial sheaths or soft tissues adjacent to tendons in the hands and feet of adults. These tumors may undergo secondary changes, including dystrophic calcification, enchondral ossification, myxoid degeneration, and hemorrhage in the lesion. Because of these changes, soft-tissue chondromas may be hard to differentiate from chondrosarcomas.
Histopathologic and clinical findings should be correlated with radiographic results. Notably, even though the changes on the plain radiographs are characteristic, in 10% of synovial chondromas, no calcification can be documented in the plain radiographs. If radiography reveals a consolidated calcified mass in the joint, a synovial chondrosarcoma should be suspected.
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Enchondroma of proximal femur.
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Plain radiograph reveals chondroma in left proximal femur (A) and low-grade chondrosarcoma in right superior pubic ramus and symphysis (B).
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MRI showing chondroma (A) and low-grade chondrosarcoma (B).
