Enchondroma

Enchondroma is a type of benign bone tumor that originates from cartilage. The exact etiology of it is not known. While it may affect an individual at any age, it is most common between the ages of 20 and 30 years. It most commonly affects the small tubular bones of the hands or feet (40%-65%), especially the proximal phalanx, followed by the middle phalanx and metacarpals. In these locations it tends to be diaphyseal. It also may affect the appendicular skeleton, especially the distal femoral shaft and proximal humerus, where it tends to be in the metaphyseal regions [1,2]. Enchondromas may also be seen in the pelvis and shoulder. Although enchondromas are typically benign and asymptomatic, they often come to attention because of complications like pathologic fracture or malignancy transformation. Transformation of asymptomatic solitary enchondromas to chondrosarcoma is unusual, although enchondromas of long bones carry a higher risk of transformation. The risk of malignancy transformation in Ollier’s disease (enchondromatosis) is 5%-30% and in Maffucci's disease (multiple hemangiomas and enchondromas) the risk is reported to be 20%. On bone scan, enchodromas typically demonstrate moderate radioisotope uptake when the lesion is actively calcifying. On plain films, enchondromas often demonstrate a lytic pattern with central radiolucency with a well-defined bony margin. Commonly, these lesions appear as a lytic area containing rings and arcs of chondroid calcifications. On X-ray or CT, enchondroma may be expansile or non-expansile but it should not destruct the cortex or extend into the soft tissues. On MRI T1-weighted images demonstrate low or intermediate signal intensity lesion and T2-weighted images demonstrate high signal intensity lesion with lobulated borders [3]. Differential diagnostic considerations are nonossifying fibroma, simple bone cyst, fibrous dysplasia, eosinophilic granuloma, and clear cell chondrosarcoma. If solitary or multiple enchondromas become symptomatic or enlarge, they may require biopsy to exclude malignancy [4].