Musculoskeletal Imaging

Enchondroma

a chondroma arising within bone. Solitary enchondromas, which develop in the medullary cavity, are usually central tumours located in the metaphysis of a long tubular bone or in the diaphysis of a short tubular bone in the hand or foot. The presence of multiple enchondromas leads to a condition termed enchondromatosis. The tumours are composed of lobules of hyaline cartilage and are often asymptomatic. If pain is present, malignant transformation should be suspected; this complication occurs more commonly in the long tubular bones and those of the pelvic and shoulder girdles. Most solitary tumours involve the hands, particularly the proximal phalanges, or feet. In addition, solitary enchondromas occur in the long tubular bones, especially the humerus, femur, tibia and innominate bones (Fig.1). Some enchondromas lead to bone expansion (enchondroma protuberans), which simulates the appearance of an osteochondroma. In adults, rib lesions may also be caused by enchondromas.

Radiographically, enchondromas of the hand or foot appear as well-defined medullary lesions with some degree of calcification, lobulation and endosteal erosion. Other features that may be present are cortical expansion and pathologic fracture (Fig.2). Enchondromas are the most common benign tumour of the hand, and the presence of a solitary, well-marginated, lobulated intraosseous lesion in the bones of the hands is highly suggestive of enchondroma. Enchondromas in the long tubular bones most typically appear on radiographs as centrally or eccentrically placed medullary osteolytic tumours of variable size with or without calcification, with lobulated erosion of the endosteal margin of the cortex. MR imaging of enchondromas usually reveals a well-circumscribed lesion of low signal intensity in T1-weighted spin-echo MR images and of high signal intensity in T2-weighted spin-echo and many gradient-echo MR images (Fig.3). Foci of calcification are observed as regions of low signal intensity.

Malignant transformation of a solitary enchondroma may sometimes occur but is more likely in tumours in the long tubular or flat bones. Chondrosarcoma is the usual result after malignant transformation of an enchondroma. Radiographic findings suggesting malignant transformation include an enlarging radiolucent area, pathologic fracture, soft tissue mass, and disappearance of pre-existing calcification within the enchondroma (Fig.4).

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Fig.1

a. AP radiograph shows punctate calcification in the humeral head and neck. b. CT scan demonstrates an osteolytic lesion with well-defined sclerotic margins and a chondroid matrix.
Enchondroma, Fig.1 (a)
Enchondroma, Fig.1 (b)
Enchondroma, Fig.2
Enchondroma, Fig.3 (a)
Enchondroma, Fig.3 (b)
Enchondroma, Fig.3 (c)
Enchondroma, Fig.4 (a)
Enchondroma, Fig.4 (b)