Enchondromas are benign cartilaginous tumors that usually form in the intramedullary region of long bones. They are common in the long bones of the hand, where tumors can cause noticeable pain. In other regions of the skeleton, enchondromas often are asymptomatic and are most commonly found incidentally on imaging studies after trauma.1–3 Although 10% of diagnosed enchondromas are found in the humerus, the true prevalence in the population is likely greater.4 In one study, the prevalence of enchondromas on routine magnetic resonance imaging (MRI) scans of the humerus was 2.1%.5 Asymptomatic enchondromas usually can go untreated with regular observation.6–9 However, rarely, when larger lesions cause pain or fracture, the recommended treatment strategy is open curettage and reconstruction with preservation of the surrounding bone.6–8,10
On diagnosis, care must be taken to differentiate enchondromas from low-grade chondrosarcomas.3,11 Histologically, it can be difficult to distinguish between them because they both have low cellularity, with a large amount of hyaline matrix formation.7,11–15 The diagnostic dilemma is even greater because of the small quantities of tissue available for review, including the modest recovery associated with core needle biopsy. However, clinical and radiologic factors can be helpful in differentiating between enchondromas and chondrosarcomas.3,7,15–21 Chondrosarcomas commonly present with pain, often dull and occurring at night.3,11,13,20,22–24 Therefore, any cartilaginous lesion presenting with pain should be approached with a high degree of suspicion for malignancy. However, at the humerus, pain may not be a useful marker for malignancy.1–3 Although enchondromas usually are asymptomatic and do not cause pain, the high incidence of painful rotator cuff pathology may lead to the discovery of incidental enchondromas on imaging. In a series of 57 humeral enchondromas, only 1 lesion presented with pain attributed to the active enchondroma. For most of the other lesions, pain was associated with other shoulder pathology.2 This diagnostic difficulty leads to an increased emphasis on proper radiologic evaluation.
Technetium-99m radionuclide bone scans often are used in the evaluation of apparent low-grade cartilaginous lesions. Uptake of this radionuclide can be seen in regions of osteoid deposition or angiogenesis, which is common with neoplastic changes in bone, such as low-grade chondrosarcomas.20,25–30 Enchondromas can show varied levels of uptake, depending on the degree of osteoid deposition and blood vessel formation.7,20,26,29–34 As a result, in the proper clinical context, the finding of low uptake on radionuclide bone scan, or a “negative” finding, can be highly specific for enchondroma, effectively excluding malignancy with high specificity. On the other hand, the finding of high uptake on bone scan, or a “positive” finding, does not exclude benign enchondroma. However, because the incidence of positive findings among enchondromas is not known, it remains to be seen whether these scans actually add utility in distinguishing between enchondromas and low-grade chondrosarcomas. The goal of the current study was to determine the utility of bone scans by reviewing the diagnostic workup of all patients with apparent well-differentiated cartilaginous lesions who were referred to one orthopedic oncology specialty practice.
Materials and Methods
A retrospective review was conducted of all patients at one academic medical center who underwent radionuclide bone scan for eventual diagnosis of enchondroma between January 2004 and December 2010. All diagnoses were made based on clinical history and imaging studies by physicians with advanced training in orthopedic oncology. Patients were followed for at least 1 year after diagnosis to confirm that there was no growth or change in the lesion. The need for informed consent was waived for this retrospective study; however, the study followed the Health Insurance Portability and Accountability Act guidelines for confidentiality and was approved by the local institutional review board.
Patient demographics and clinical presentation data were collected, including patient age, sex, location of lesion, and presence of pain or fracture on presentation. Radiographs and MRI scans were reviewed for evidence of aggressive features, including soft tissue involvement, endosteal scalloping, and periosteal involvement.
For all bone scans, radiology reports were reviewed to determine whether increased radionuclide uptake was observed at the site of the lesion and whether increased uptake was “mild” or “significant.” In practice, this determination was made by radiologists based on comparison with normal radionuclide uptake seen at the iliac crest. Bivariate logistic regression was used to determine the association of bone scan results with endosteal scalloping, an aggressive feature, on radiographs and MRI scans.
All statistical analyses were performed with Stata version 13.0 software (StataCorp, LP, College Station, Texas). All statistical tests were two tailed, and the level of significance was set at alpha=0.05.
During initial evaluation, 25 patients with an eventual diagnosis of enchondroma underwent radionuclide bone scanning (Table 1). The lesions showed no progression during average follow-up of 69 weeks. Mean age was 50 years (range, 25–64 years). For 23 patients (92%), enchondroma was an incidental finding on imaging. For 2 patients (8%), enchondroma was diagnosed as a result of pain, apparently from the site of the lesion. All patients were treated conservatively and followed with serial radiographs to confirm that the lesion did not progress.
Patient and Lesion Characteristics
On bone scan, 18 patients (72%) had positive findings at the site of the enchondroma (Table 1), 5 patients (20%) had weakly positive findings, and 2 patients (8%) had negative findings.
For all patients, radiographs were obtained during workup, and 2 patients (8%) showed endosteal scalloping (Table 1). The other patients showed no aggressive features on radiographs. Five patients (20%) showed calcifications, although this is not a sign of an aggressive lesion. Of the 22 patients who had MRI scans during workup, 4 patients (18%) showed endosteal scalloping. The other patients (82%) had no aggressive features on MRI. No statistically significant association was seen between positive findings on bone scan and aggressive features on radiograph (P=.485), MRI scan (P=.398), or in general (P=.310; Table 2).
Association of Positive Bone Scan Results With Aggressive Features
When treating patients with low-grade cartilaginous lesions, differentiating between benign and malignant lesions is critical. In the humerus, imaging may be especially important because pain from concurrent rotator cuff pathology may be difficult to differentiate from a painful, metabolically active chondrosarcoma. Often radionuclide bone scans are obtained during workup.7,16,19,20,26,29,30,35 Chondrosarcomas consistently show high levels of radionuclide uptake on bone scan.17,19,20,27,29,35 However, with enchondromas, uptake can be variable, ranging from no increased uptake to high uptake, depending on osteoid deposition and angiogenesis.7,20,26,29–34
In the current series, unlike chondrosarcomas, only 2 of 25 of enchondromas showed negative findings on bone scan. In the current study population, radionuclide bone scans had only 8% sensitivity for the diagnosis of enchondromas. With such low sensitivity for differentiating enchondromas from low-grade chondrosarcomas, routine use of radionuclide bone scans is likely unwarranted. Increased uptake seen on bone scans represents regions of osteoid deposition or angiogenesis.20,25–30 This finding is common in benign enchondromas, which may have increased metabolism compared with normal bone.
An additional finding of the current study was that positive findings on bone scan in an enchondroma showed no statistically significant association with aggressive features seen on radiograph or MRI scan. These features, which include endosteal scalloping, periosteal reaction, cortical destruction, remodeling, and soft tissue invasion, have been well correlated with disease progression.7,9,16,17,19–21,36 In the current population, 92% of enchondromas had no aggressive features on radiograph, and 82% of patients who underwent MRI scan showed no aggressive features. Further, in suspected low-grade lesions, aggressive features do not necessitate immediate surgical intervention.3,6,8 In the current series, the 6 patients who showed endosteal scalloping were followed with imaging at regular intervals to ensure that no disease progression occurred.
Although radionuclide bone scanning has low utility for differentiating between enchondromas and low-grade chondrosarcomas, bone scans may have value in identifying multiple bony lesions. In cases of enchondromatosis, such as Ollier's disease or Maffucci syndrome, in which patients have multiple benign cartilage lesions, radionuclide bone scan can be used to judge the extent of disease and find previously unidentified lesions.37 For these patients, whole body scans highlight lesions throughout the body that may suggest malignant transformation and require further evaluation. Even in these cases, care must be taken not to infer whether a lesion is benign or malignant, based on increased uptake on bone scan. Even in the context of aggressive enchondromatosis, lesions with high uptake do not indicate malignancy.32
The primary limitation of this study was that the authors did not have bone scan results from patients with similar clinical presentation who had low-grade chondrosarcomas. Without this comparison, it is impossible to report on the positive or negative predictive value of radionuclide bone scans in diagnosing enchondromas. Nevertheless, in this population, sensitivity was 8% for confirming the diagnosis of enchondroma, representing minimal utility in routine workup of low-grade cartilaginous lesions.
Based on the current findings and given the utility of patient presentation, plain radiographs, and MRI scans in the diagnosis of these lesions, regular use of radionuclide bone scans for workup of well-differentiated cartilaginous lesions is not warranted. Physicians who have experience in the diagnosis of musculoskeletal tumors may rely instead on the clinical and radiographic findings, with regular observation over time to ensure that there is no disease progression.
Numerous radiographic signs of local aggressiveness have been described that may be used in differentiating low-grade chondrosarcomas from enchondromas. Chondrosarcomas usually show signs of soft tissue inflammation, endosteal scalloping, or periosteal involvement.7,9,16,17,19–21,36 Suspected enchondromas that do not show these aggressive features on radiographs can be observed over time with serial radiographs to monitor for these signs.3,6,8,9 Because of the low specificity of clinical pain in diagnosing chondrosarcomas, radiologic features are critical in the diagnosis of cartilaginous humeral lesions. In addition to radiographs, other imaging modalities have been used, including MRI scans,7,10,35,36 computed tomography,7,35,38 and radionuclide bone scans.7,16,19,20,26,29,30,35
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- Hong ED, Carrino JA, Weber KL, Fayad LM. Prevalence of shoulder enchondromas on routine MR imaging. Clin Imaging. 2011;35(5):378–384. doi:10.1016/j.clinimag.2010.10.012 [CrossRef] PMID:21872128
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- Qasem SA, DeYoung BR. Cartilage-forming tumors. Semin Diagn Pathol. 2014;31(1):10–20. doi:10.1053/j.semdp.2014.01.006 [CrossRef] PMID:24680178
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- Normand AN, Cannon CP, Lewis VO, Lin PP, Yasko AW. Curettage of biopsy-diagnosed grade 1 periacetabular chondrosarcoma. Clin Orthop Relat Res. 2007; 459(459):146–149. doi:10.1097/BLO.0b013e3180619554 [CrossRef] PMID:17452919
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Patient and Lesion Characteristics
|Patient Age at Diagnosis, y||Location of Lesion||Presentation||Bone Scan Findings||Radiographic Findings||Magnetic Resonance Imaging Findings||Management|
|48||Metaphyseal||Incidental finding||Negative||No aggressive features||No aggressive features||Observation|
|51||Metadiaphyseal||Incidental finding||Negative||Endosteal scalloping||No aggressive features||Observation|
|25||Metadiaphyseal||Incidental finding||Weakly positive||Calcifications/no aggressive features||No aggressive features||Observation|
|39||Metadiaphyseal||Incidental finding||Weakly positive||No aggressive features||No aggressive features||Observation|
|46||Metadiaphyseal||Incidental finding||Weakly positive||No aggressive features||Endosteal scalloping||Observation|
|59||Metaphyseal||Incidental finding||Weakly positive||No aggressive features||Endosteal scalloping||Observation|
|63||Metadiaphyseal||Incidental finding||Weakly positive||No aggressive features||No aggressive features||Observation|
|33||Metaphyseal||Incidental finding||Positive||Calcifications/no aggressive features||Not performed||Observation|
|38||Metadiaphyseal||Pain||Positive||Endosteal scalloping||No aggressive features||Observation|
|38||Metadiaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|44||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|45||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|45||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|46||Metaphyseal||Incidental finding||Positive||Calcifications/no aggressive features||No aggressive features||Observation|
|50||Metadiaphyseal||Incidental finding||Positive||No aggressive features||Endosteal scalloping||Observation|
|52||Metaphyseal||Incidental finding||Positive||No aggressive features||Not performed||Observation|
|52||Metaepiphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|53||Metaphyseal||Pain||Positive||No aggressive features||No aggressive features||Observation|
|58||Epiphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|58||Metaphyseal||Incidental finding||Positive||No aggressive features||Endosteal scalloping||Observation|
|60||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|62||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
|63||Metaphyseal||Incidental finding||Positive||Calcifications/no aggressive features||Not performed||Observation|
|64||Metaphyseal||Incidental finding||Positive||Calcifications/no aggressive features||No aggressive features||Observation|
|64||Metaphyseal||Incidental finding||Positive||No aggressive features||No aggressive features||Observation|
Association of Positive Bone Scan Results With Aggressive Features
|Outcome||No./Total No.||Odds Ratio (95% CI)||P|
|Aggressive features on radiograph||2/25 (8%)||0.35 (0.02–6.57)||.485|
|Aggressive features on MRI||4/22 (18%)||0.38 (0.04–3.52)||.398|
|Any aggressive featuresa||7/25 (28%)||0.38 (0.06–2.46)||.310|