Fortunately, Enchondroma Lesions Are Rarely Malignant
Although transformation of a solitary enchondroma to malignancy is rare, any concern for possible malignancy should prompt referral to a major musculoskeletal tumor center.
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In the world of orthopaedic oncology, differentiating benign lesions from those with a more menacing natural history is important. One of the most common bone lesions discovered as an incidental finding is the benign cartilage lesion known as the enchondroma. With at least 85 percent remaining asymptomatic, these lesions are typically found on routine multimodal imaging studies during investigations of activity-related musculoskeletal complaints, such as a sports injury to the rotator cuff or knee, or arthritis of a joint.
Understanding the presentation and appearance of these benign lesions is important, as it will direct future care and may help ease anxiety and quell uncertainty in the patient with a newly discovered bone lesion. Although transformation of a solitary enchondroma to malignancy is rare, any concern for possible malignancy should prompt referral to a major musculoskeletal tumor center.
The enchondroma lesion itself is made up of a benign growth of hyaline cartilage. Its exact cause is unknown. It displays equal prevalence in males and females between ages 20 and 50, when it is often discovered, although enchondroma lesions may begin to grow in early childhood. There is no sex predilection, and since most enchondromas are asymptomatic, the true prevalence and most frequent age of onset are unknown. Common locations for enchondromas include the metatarsal and metacarpal bones, distal femur (Figure 1) and proximal humerus (Figure 2).
Less than 15 percent of enchondromas are symptomatic (active). Active lesions are painful and may increase the risk for pathologic fracture if associated with cortical thinning (endosteal scalloping). A patient with constitutional symptoms (e.g., night sweats, weight loss, nocturnal pain) should be evaluated aggressively for malignant transformation. Associated soft-tissue masses are indicative of either fracture hematoma or chondrosarcoma transformation.
Understanding the common radiographic findings for a benign lesion is important. Although extremely rare (< 1 percent incidence), malignant transformation of an isolated enchondroma has been described. A basic understanding of benign radiographic characteristics can aid in determining the possibility of malignant progression.
Plain radiographs should always be interpreted in the context of the history and physical exam. Enchondromas most commonly appear as elongated intramedullary lesions located in a centralized position of the metaphyseal and metadiaphyseal regions. They typically are solitary, well-formed lesions with a calcified matrix resembling popcorn (the exception is enchondromatosis; see below). Hand enchondromas are more commonly radiolucent but can also display punctate stippling in conjunction with cortical thinning (though rarely cortical destruction). Typically, periosteal reaction is seen only with associated pathologic fracture. A representative radiographic differential diagnosis for enchondroma should include low-grade chondrosarcoma and bone infarct. In general, after skeletal maturity, enchondromas do not grow and rarely cause pain.
Endosteal scalloping may occur with enchondromas. Anteroposterior and lateral plain film evaluation should be undertaken initially. Scalloping may be incidental or, if severe enough, may lead to undue cortical stress and, in rare instances, pathologic fracture. Soft-tissue or extracortical masses associated with an enchondroma should heighten suspicion for potential transformation to a chondrosarcoma.
Although solitary enchondromas are largely the rule, multiple foci of enchondromas in a single patient can be found in syndromes such as Maffucci’s syndrome and Ollier’s disease (enchondromatosis). Maffucci’s syndrome is characterized by soft-tissue hemangiomas and multiple enchondromas, often in the hands but also involving long bones. Radiographic clues include calcified soft-tissue phleboliths within the hemangiomas, as well as aggressive-appearing multifocal lytic bone lesions. In both Maffucci’s syndrome and Ollier’s disease, angular and rotational deformities can be caused by lesions involving the growth plates. A sudden increase in pain and destructive cortical changes are worrisome for malignant transformation. Both syndromes are associated with an increased risk of secondary chondrosarcoma, with incidence as high as 30 percent in Ollier’s disease and up to 50 percent in Maffucci’s syndrome.
Though it is rare in solitary enchondromas, malignant transformation must always be considered. Clues that signal a potential for malignant degeneration include greater than 50 percent endosteal scalloping, full-thickness cortical destruction (Figure 3), periosteal changes and associated soft-tissue masses. Isolated pelvic enchondromas are extremely rare, and any enchondroma-like lesion in the pelvis warrants suspicion for a potential chondrosarcoma. Beyond plain films, CT scans are helpful for evaluating the degree of endosteal scalloping, and MRI is most reliable in delineating the true extent of intramedullary or extracortical involvement in conjunction with any soft-tissue mass (Figure 4). Bone scans are largely nonspecific in diagnosing solitary enchondromas (due to a near-universal propensity for increased uptake) but may be helpful in recognizing the patient with multiple enchondromatosis.
Since most enchondromas are incidental findings, management usually consists of regular follow-up via serial radiographs, with observation being the treatment of choice for most lesions that are asymptomatic. Any questionable lesion-associated pain may be distinguished from periarticular pathology with a simple intra-articular injection. An adequate biopsy is indicated in lesions with associated pain and worrisome radiographic characteristics (i.e., full-thickness cortical destruction) for a low- or intermediate-grade chondrosarcoma. Definitive diagnosis often requires more than a needle biopsy, with a clear-cut diagnosis often depending on the permanent pathology. As in the management of all sarcomatous lesions, the surgeon who will be doing the definitive surgery should be involved early, with the patient referral made prior to biopsy. Intralesional curettage and use of adjuvant therapy (e.g., liquid nitrogen, phenol) for low-grade extremity chondrosarcoma have produced excellent long-term results, with recurrence rates of approximately 6 percent (J Bone Joint Surg Am. 2012;94:1201-1207).
The incidence of benign bone lesions far surpasses the number of diagnosed sarcomas. Although the vast majority of enchondromas will remain indolent over the patient’s lifetime, every orthopaedic surgeon should be familiar with the diagnostic characteristics of common bony and soft-tissue lesions. Any concern for possible malignancy should initiate a referral to a major musculoskeletal tumor center, such as Cleveland Clinic. In the vast majority of cases, the good news you convey to the patient concerning the benign characteristics of his or her lesion will dispel uncertainty and provide reassurance. The welcome words “It’s not cancer” will reliably bring a smile to the face of patient and provider alike.
Dr. David Joyce is a PGY-6 orthopaedic resident at Cleveland Clinic and will be pursuing an orthopaedic trauma fellowship at Vanderbilt University.
Dr. Mesko is a staff physician in the Department of Orthopaedic Surgery’s Musculoskeletal Tumor Center.
Dr. Ilaslan is Assistant Professor of Radiology in Cleveland Clinic’s Imaging Institute.
Dr. Lietman, Co-Director of the Musculoskeletal Tumor Center, specializes in orthopaedic oncology and adult reconstruction.
Dr. Michael Joyce, Co-Director of the Musculoskeletal Tumor Center, specializes in trauma, oncology, total joint replacement and musculoskeletal tissue banking.