Enchondroma

• General considerations
• Benign cartilaginous tumor
• Develops in the medullary cavity
• Usually solitary, although they can occur as multiple lesions in syndromes to be discussed
• Arise from ectopic rests of hyaline cartilage
• Occur mostly in 2nd to 3rd decade
• Most common site is small bones of the hands and feet
• Most occur in the proximal phalanx
• Most common tumor of the hand
• Also occur in the humerus, femur, tibia and ribs
• In long bones, their calcification is similar to an intramedullary bone infarct
• Bone infarcts tend to have a well-circumscribed, sclerotic margin
• May fracture or, rarely, undergo malignant transformation
• On CT, lucent regions in an otherwise dense enchondroma suggest malignancy
• Rapid growth of lesion or pain not related to a pathologic fracture may  suggest malignant transformation
• Clinical findings
• Usually asymptomatic and found serendipitously
• May be associated with pain and swelling which should raise suspicion of either a pathologic fracture or, less likely, malignant transformation
• Malignant transformation almost never occurs in the hands and feet
• Imaging findings
• Conventional radiography is the study of first choice
• Well-defined lytic and slightly expansile lesion (in small bones)
• Usually have some internal calcification and endosteal thinning
• Internal calcifications tend to resemble “rings and arcs” of cartilage calcification
• MRI findings
• Numerous internal foci with high-signal intensity on T2
• Low to intermediate signal on T1
• Lobulated in contour
• Bone scan
• Negative if uncomplicated enchondroma
• Multiple enchondromas occur in Ollier's disease
• Nonhereditary
• Frequently unilateral
• Enchondromas are frequently larger than with solitary enchondroma
• May have limb shortening of affected limb
• May have Madelung’s deformity of the wrist
• Greater incidence of malignant transformation because there are more lesions present (25-50%)
• Enchondromas associated with cavernous hemangiomas of soft tissues is called Maffucci’s Syndrome
• Nonhereditary
• Even more rare than Ollier’s disease
• Multiple hemangiomas usually in extremities (digits)
• Look for phleboliths in hemangioma
• Growth disturbance of affected bones
• Malignant transformation
• Greater than solitary enchondroma, less than Ollier’s
• Hemangioma may become sarcoma in 5% of cases

Enchondroma with pathologic fracture. Left: There is a non-displaced fracture through the base of the proximal phalanx of the 4th toe (white arrow). Right: A well-defined, slightly expansile, lytic lesion is seen in the proximal phalanx (white circle) through which the fracture has occurred.
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