Enchondroma is a solitary, benign, intramedullary cartilage tumor that is usually found in the short tubular bones of the hands and feet. The peak incidence is in the third decade and is equal between men and women.

It is the most common primary tumor in the hand and is normally found in the diaphysis. The mature hyaline cartilage located centrally within short tubular bones usually presents clinically as a fracture due to an enlarging lesion. Enchondromas are also found incidentally in long bones and undergo malignant transformation in less than 1% of cases.
Multiple enchondromatosis is a non-heritable condition also known as Ollier's disease. Multiple enchondromas and hemangiomas of soft tissue are otherwise known as Maffucci's Syndrome. In both conditions, males are affected more than women and the disease process often only affects one side of the body. In both diseases, there is a 30% risk of malignant transformation of the enchondromas.  Enchondromas are difficult to differentiate from low grade chondrosarcoma by radiology. Lesions located near the shoulder or the pelvis may have a higher risk of sarcomatous degeneration (Krikun). Chondrosarcoma is much more common in older patients, so large enchondromas in older individuals demand a careful work-up.
Enchondromas are usually long and oval and have well-defined margins. In larger lesions, the lucent defect has endosteal scalloping and the cortex is expanded and thinned. Calcifications throughout the lesion can range from punctate to rings. CT is useful for detecting matrix mineralization and cortex integrity. MRI is helpful for describing the non-mineralized portion of the lesion and visualizing any aggressive or destructive features.

Radiographic and imaging features of enchondroma that are considered worrisome due to the potential for malignancy include large size, a large unmineralized component, significant thinning of the adjacent cortex, and bone scan activity greater than that of the anterior superior iliac spine.
Features of enchondroma that are very strongly associated with malignant transformation are progressive destruction of the chondroid matrix by an expanding, non-mineralized component, an enlarging lesion associated with pain, or an expansile soft tissue mass.
On gross examination, an enchondroma consists of bluish-gray lobules of fine translucent tissue. The degree of calcification of the lesion determines if the consistency is gritty.Under the microscope, a thin layer of lamellar bone surrounding the cartilage nodules is a positive sign that the lesion is benign. At low power, there are lobules of different sizes. Blood vessels are surrounded by osteoid. Enchondromas have chondrocytes without atypia inside hyaline cartilage. The nuclei are small, round and pyknotic. The cellularity varies between lesions and within the same lesion.

Each potential enchondroma needs to be evaluated for cellularity, nuclear atypia, double nucleated chondrocytes and mitotic activity in a viable area without calcifications to distinguish it from low-grade chondrosarcoma. Small peripheral lesions are more likely to be benign than large axial lesions. The pathologic diagnosis is so difficult it always needs to be made in conjunction with the radiologist and the surgeon.

A solitary painless enchondroma may be observed. Painful or worrisome lesions should be treated with biopsy followed by intralesional resection. Large defects can be filled with bone graft. All specimens must be analyzed carefully for malignancy.

Gitelis, S. et al, Benign Bone Tumors, Instructional Course Lectures, 45:p. 426-46, 1991.

Giudici, A. et al, Cartilaginous Bone Tumors, Radiologic Clinics of North Amenca, 31(2):p. 237-259, March 1993.

Bullough, Peter. Orthopaedic Pathology (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors: Diagnosis, Treatment and Prognosis, W.B. Saunders, Co., 1991.

Krikun M. Imaging of Bone Tumors Philadelphia, W.B Saunders, 1993

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