Enchondroma

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.

References
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

Adapted, with permission from bonetumor.com By Henry DeGroot III, M.D.