Excerpt from Enchondroma and Enchondromatosis

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Background

Enchondromas are benign cartilaginous neoplasms that are usually solitary lesions in intramedullary bone. The primary significant factors of enchondromas are related to their complications, most notably pathologic fracture, and a small incidence of malignant transformation, which may be associated with pathologic fracture.

When multiple enchondromas coexist, the diagnosis of enchondromatosis should be considered.

Multiple enchondromas may occur in 3 distinct disorders:

• Ollier disease is a nonhereditary disorder characterized by multiple enchondromas with a predilection for unilateral distribution. The enchondromas can grow large and can be disfiguring.
• Maffucci syndrome is nonhereditary and is less common than Ollier disease. This syndrome results in multiple hemangiomas in addition to enchondromas.
• Metachondromatosis consists of multiple enchondromas and osteochondromas. Of the 3 disorders, metachondromatosis is the only one that is hereditary, which is by autosomal dominant transmission.

Pathophysiology

Enchondromas are ectopic hyaline cartilage rests in intramedullary bone. The lesions replace normal bone with mineralized or unmineralized hyaline cartilage, thereby generating a lytic pattern on radiographs or, more commonly, a lytic area containing rings and arcs of chondroid calcifications. The lesions likely arise from cartilaginous rests that are displaced from the growth plate.

Endosteal growth may occur and does not imply malignant transformation in the hands and feet, wherein the lesions appear to be more cellular. Although the extent of cellularity is not correlated with malignant transformation, mitotic figures are seldom seen in the lesions, and their presence may be correlated with malignancy. Pathologic fracture predisposed by thinning of the cortex is not typically associated with malignancy in the hands and feet; however, in other areas such as the long bones and flat bones, pathologic fracture is suggestive of malignant transformation.

Complete transgression through the cortex with a soft-tissue component is highly suggestive of malignancy. Although malignant transformation to several types of tumors is reported, chondrosarcoma is the most common by far.

Frequency

United States

Enchondromas account for 12-14% of benign bone neoplasms and 3-10% of osseous neoplasms in general (Unni, 1996).

Mortality/Morbidity

Most often, enchondromas are of no consequence and patients are asymptomatic. Enchondromas are not life threatening; however, painful malignant transformation should be the primary concern and cannot be excluded, even in the presence of a benign appearance on radiographs and images from other modalities. Malignant transformation is virtually nonexistent in the hands and feet but may be seen in the long bones and flat bones.

• In a patient with enchondromatosis, the incidence of chondrosarcoma is much higher than in other patients, and the rate may be as high as 50% (Unni).
• In Maffucci syndrome, hemangiomas also may undergo sarcomatous transformation; however, osseous lesions do so more frequently and most commonly result in chondrosarcomas.
• In the event of malignant transformation to chondrosarcoma, patients with low-grade chondrosarcoma have a 5-year survival rate of 65-85%, whereas patients with the highest-grade chondrosarcomas have a 5-year survival rate of 15% (Springfield et al, 1996).

Race

No racial predilection is known.

Sex

Enchondromas occur equally in males and females.

Age

Solitary enchondromas most often are discovered in those aged 20-40 years. Ollier disease is usually detected in those aged 0-10 years.

Anatomy

Solitary enchondromas are intramedullary lesions, although they may expand enough to cause endosteal scalloping of the cortex. They have a predilection for the small bones of the hands and feet, where most occur. Of these, half are in the proximal phalanx, followed in frequency by the metacarpal and middle phalanx and, lastly, by the distal phalanges and carpus. Other locations are the shoulder, pelvis, and long bones. Enchondromas tend to occupy the diaphyseal region in the short tubular bones and the metaphyseal region in the longer bones. Ollier disease occurs with highest frequency in the long bones.

Approximately 50% of solitary enchondromas are found in the hands, typically in the middle and distal portions of the metacarpals and the proximal portions of the phalanges (Unni). The next most common sites are the proximal and distal parts of the femur and the proximal part of the humerus. Enchondromas at the mid shaft of the tibia are rare.

Clinical Details

When patients have pain and/or rapid growth of the lesion, malignant transformation should be suspected, even in the absence of suggestive radiographic findings. Enchondromas are metabolically active and may continue to grow and evolve throughout the patient's lifetime; thus, progressive calcification over a period of years is not unusual. Loss of calcification in a focal region suggests malignant degeneration with destruction of the underlying enchondroma by sarcomatous tissue.

Primary clinical complications include pathologic fracture and malignant transformation, which may be concomitant. In particular, pathologic fracture does not imply malignant transformation in the hands and feet, in which endosteal scalloping and cortical thinning may be extensive without malignant transformation.

When the lesion has calcifications, the primary differential diagnoses are bone infarct and chondrosarcoma. When the lesion is purely lytic, as shown on radiographs, the differential diagnosis consists of benign lytic lesions such as nonossifying fibroma, simple bone cyst, fibrous dysplasia, eosinophilic granuloma, and clear cell chondrosarcoma (which tends to involve the end of the bone—in particular, the proximal humerus).

Preferred Examination

Initially, radiography is the imaging modality of choice. If further characterization is necessary, magnetic resonance imaging (MRI) or computed tomography (CT) scanning is performed. If uncertainty remains, bone scanning may be helpful, but some lesions require biopsy.

Limitations of Techniques

X-ray findings may not demonstrate or adequately characterize subtle calcifications to the extent that CT scans do. When calcifications are not present on either examination, MRI may be performed, which should reveal the classic appearance of noncalcified hyaline cartilage. Dystrophic calcifications in bone infarcts may be difficult to differentiate from chondroid matrix with ionizing radiation, and MRI may be helpful in these cases.

Occasionally, dystrophic calcifications in bone infarcts may be difficult to differentiate from enchondromas on plain radiographs. When a clearly serpiginous rind of sclerosis encapsulates the lesion, the diagnosis of bone infarct is straightforward; however, when this finding is not present, MRI may be useful in differentiating the 2 entities.

In lesions in which calcifications are not seen radiographically, the diagnosis may be made with the help of MRIs. CT scans may demonstrate the presence of calcification not depicted on radiographs.

Chondrosarcoma—in particular, low-grade chondrosarcoma—may be indistinguishable from enchondroma. Certain imaging features may be helpful in distinguishing enchondroma from chondrosarcoma (see Radiograph section below). However, even a lesion with no imaging features suggestive of malignancy and an imaging appearance compatible with an enchondroma should be resected when it is associated with pain. Low-grade chondrosarcoma may be indistinguishable from enchondroma on all images, and the diagnosis may be difficult, even with histologic evaluation.

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