Enchondromas of Long Bones and Other Skeletal Lesions Found Incidentally Need Critical Evaluation, But Rarely Systematic Follow-Up ()
1. Introduction
Each case presenting with an incidental finding in musculoskeletal imaging raises concern regarding diagnosis and further management.
Among the series of incidental bone findings referred to our tumor group for evaluation cartilaginous tumors were the most frequent, usually referred with the objective to “rule out sarcoma”.
Several authors (Patel et al. [1], Davies et al. [2], and Ahmed et al. [3]) recently questioned, whether follow-up imaging is needed in incidentally found painless chondroid lesions in long bones without aggressive features in imaging.
Historically the risk of developing chondrosarcoma ex enchondroma has been overestimated, as enchondromas were detected in standard radiographs only in the presence of distinct calcifications. In the era of MRI, enchondromas are found more frequently, and with a prevalence of 2.8% in knee MRI according to Stomp et al. [4] may be regarded as a “normal concurrent finding”.
With our data, we wish to contribute to the discussion of how to proceed with enchondromas found incidentally regarding follow-up. We also include the other incidental bone lesions to expand on differential diagnostic aspects.
2. Materials and Methods
Patients
153 cases have been referred by orthopaedic surgeons to our dedicated musculoskeletal tumor group for the evaluation of incidental bone findings from July 2008 through June 2021. Imaging was performed in most patients because of shoulder or knee problems. All patients had standard X-Ray and MRI documentation. The diagnoses as an incidental finding were based upon the patients’ history and physical examination and are summarized in Table 1.
Based on X-Ray and MRI 73 of the patients had cartilaginous tumors and 63 of these were diagnosed as enchondroma of a long bone. One of the 63 had bilateral enchondromas in the distal femur. Histologic examinations were performed on 5 of the 63 enchondroma cases. One humeral lesion was curetted elsewhere for suspected chondrosarcoma and eventually diagnosed as enchondroma without atypia; one patient with a distal tibia enchondroma had a biopsy as an external radiology expert felt another entity needed to be ruled out.
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Table 1. List of incidentally found bone lesions regarding diagnosis, size of the enchondromas, management and follow-up data.
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Figure 1. Female, 60 years: Enchondroma. MRI for rotator cuff evaluation. Proton-density-fat-saturated images show the enchondroma with a length of 63 mm unchanged over 2.8 years.
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Figure 2. Male, 63 years: Enchondroma. MRI for evaluation of meniscal problems. The length (126 mm) and structural characteristics of “rings and arcs” remained unchanged over 7 years. In 2015 only sagittal images were provided. Clinically the patient is asymptomatic in 2021.
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Figure 3. Female, 50 years: Enchondroma. Knee MRI for evaluation after contusion of the knee joint. The presentation of two separate lesions is unusual, but the images are typical for a chondroid matrix with inhomogenous contrast enhancement in the T1 weighted fat saturated images. No increase in size over the 4.5 years follow-up (top 2016, bottom 2020).
Two enchondroma cases of the femur found incidentally were curetted and filled with bone to prepare for later knee replacement or cruciate ligament reconstruction respectively; one proximal fibula enchondroma was curetted elsewhere.
One 30-year-old patient with an atypical radiological finding in the MRI performed for suspected ligament injury from distorsion of the knee joint (Figure 4) was eventually diagnosed as chondrosarcoma grade II of the medial tibial plateau and treated by wide resection and endoprosthetic reconstruction.
It is mandatory to report any malignant tumor including atypical chondromatous lesions to the Swiss Confoederation Cancer Registry. None of the patients of this study has been recorded up to January 2022, thus further documenting uneventful development.
Other cartilaginous lesions considered to be enchondromas type Ollier (n = 3), and osteochondromatous lesions are listed for completeness.
Follow-up with imaging had been recommended to the referring colleagues at first presentation. Request for follow-up information was written at the time of this study. Patients were also asked for information about their present health.
3. Results
Follow-up imaging is available for 35 of the 63 enchondroma patients at 1 to 13 years (mean 4.3 years) with no change in size, except for one femoral diaphyseal enchondroma with increasing diameter from 3.4 mm at age 18 years to 4.2 mm at age 20 years. 14 patients answering to personal contact by phone or letter responded to have remained asymptomatic at follow-up over 2 to 12 years (mean 5.6 years). 14 patients could not be contacted because of having moved to an unknown address.
The data of the enchondroma and non-enchondroma lesions are summarized in Table 1. MRIs of representative cases of enchondroma, chondrosarcoma, fibrous dysplasia and non-ossifying fibromas are presented in Figures 1-6.
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Figure 4. Male, 31 years: Chondrosarcoma grade II. MRI performed for suspected meniscal lesion after distorsion of the knee joint. The pattern is consistent with a ring-and-arc chondroid matrix. However, it exhibits aggressive features such as endosteal scalloping and soft tissue extension. Furthermore, the intraepiphyseal location must raise suspicion for an atypical process.
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Figure 5. Female, 23 years: Fibrous dysplasia. Arthro-MRI was performed for suspected labral lesion. Localized defect in osteoblastic differentiation and maturation with replacement of normal bone by large fibrous stroma. Coronal proton density weighted image with fat saturation (left) showing higher signal compared to the T1 weighted image (right). Physiologic signal in the femoral head and greater trochanter.
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Figure 6. Male, 19 years: Large non-ossifying fibroma/fibrous cortical defect. This lesion already “matured” with ossification and consequently low signal on all sequences; T1 (a); proton density weighted (b); T1 fat-saturated and contrast enhancement (c).
4. Discussion
The purpose of this study is to assist in the decision making when faced with an incidental long bone finding presented to a musculoskeletal specialist.
Extensive literature upon the question of how to manage incidental orthopaedic findings exists; we, therefore, cite only a few selected references (Kim et al. [5], Velasco et al. [6], Nguyen et al., [7], Hiremath et al. [8], du Preez et al. [9]). Vanel et al. [10], Notrott et al. [11]).
Until recently follow-up imaging of incidentally found enchondromas has been generally considered mandatory. Since this strategy has been challenged by Ahmed et al. [3], we wish to contribute to this question with our data. In addition, we want to shed some light on other incidental bone findings.
Diagnoses encountered in our cases have been as follows.
4.1. Enchondroma
Tumors producing a chondroid matrix are histologically classified as cartilaginous neoplasms (Fletcher et al. [12]) and comprise a spectrum ranging from resting lesions to highly aggressive malignant neoplasms. Enchondroma, periosteal chondroma, enchondromatosis (Ollier and Maffucci Syndrome) and osteochondroma (“exostosis”) are benign tumors grouped together as chondromas, pathologically sharing hyaline cartilage. Chondroblastoma, chondromyxoid fibroma and synovial chondromatosis also exhibit cartilaginous differentiation.
Chondrosarcomas are malignant cartilage-differentiating tumors graded usually II or III.
Enchondromas are benign cartilaginous neoplasms that develop within the medullary space of bone and are derived from growth plate chondrocytes in bone (Milgram et al. [13], Zhang et al. [14]). Enchondromatous lesions continuing to grow and exhibiting destructive features have historically been reported as low- grade chondrosarcoma, grade 1. However, as they do not metastasize and therefore don’t fulfill criteria for malignancy, recently they are reported as central atypical cartilaginous tumor and should no longer bear the label “sarcoma” (WHO Classification of Tumours [12].
The differentiation between enchondroma and central atypical cartilaginous tumor hinges on imaging features as the histology may be identical (Nguyen et al. [7]). Aggressive features suggesting chondrosarcoma include endosteal scalloping more than two third of length of the lesion, large non-calcified component, and larger lesions (Murphey et al. [15], Choi et al. [16]). Choi et al. [16] in their study of 18 patients with low-grade chondrosarcoma and 16 patients with enchondroma, both groups with histo-pathological examinations, found higher incidence of predominantly intermediate signal in T1-weighted images, multilocular appearance on contrast-enhanced T1-weighted images, cortical destruction, soft tissue mass and adjacent abnormal bone marrow and soft tissue signal among the low-grade chondrosarcoma cases.
Scalloping is seen in most cases of proximal fibula and humeral head enchondromas, which may be explained by the thin cortex, and in these locations not necessarily indicate aggressiveness.
However, there are no clear-cut imaging criteria to separate enchondroma from low-grade chondrosarcoma with a high interobserver inconsistency regarding diagnosis and grading (Geirnaerdt et al. [17]), Jones et al. [18], Gelderblom et al. [19], Deckers et al. [20], Eefting et al. [21]).
Endosteal scalloping was found to allow differentiation between enchondroma and chondrosarcoma when involving more than one-third of the lesion (Murphey et al. [15]). Longitudinal tumor extent more than 5 cm was found to be a predictable indicator of malignancy (Geirnaerdt et al. [17]).
However, the data indicate a low risk for the evolution from quiescent enchondroma to a more active atypical chondromatous lesion (a nomenclature now replacing the description as low grade (I) chondrosarcoma). They are therefore actually considered as “leave alone lesions”; patients should be informed about the benign nature and to watch development and present again, when the incidental lesion becomes symptomatic.
The data furthermore do not support the recommendation of curettage of enchondromas and atypical chondromatous tumors still frequently advocated (e.g. Deckers et al. [22]) which is associated naturally with a certain rate of complications.
If control of the incidental lesion by repeat imaging is recommended this should be at long intervals, e.g. 3 to 5 years. First, this would save expenses and secondly this warrants that the patient does not get “tired” from follow-up before changes can be expected.
The few lesions found larger than 5 cm longitudinal extent in our patients even in the presence of scalloping showed no progression within the time frame of observation (Figures 1-3).
4.2. Other Incidentally Found Lesions
Osteochondromas are readily diagnosed and except for cases with a large cartilaginous cap can be resected without further preoperative investigations (WHO classification of Tumours [12]). The terminology “(osteo-)cartilaginous exostoses” is not any longer recommended (WHO classification of Tumours [12]).
Fibrous dysplasia typically presents an incidental finding in its monostotic form. Follow-up consultation is needed only when symptoms develop (DiCaprio et al. [23]).
The liposclerosing myxofibrous tumor (LSMFT) is a benign fibro-osseous lesion, has distinct radiographic features and is generally diagnosed incidentally (Deel et al. [24]). Heim et al. [25] proposed that LSMFT probably represents a traumatized variant of fibrous dysplasia and involutional/ischemic changes can be so extensive that residual fibrous dysplasia areas are completely absent.
Non-ossifying fibromas are easily diagnosed and rarely need intervention, but apparently, even orthopaedic surgeons may have difficulties to make the diagnosis especially in larger lesions (Herget et al. [26]).
The so-called periosteal desmoids are mentioned as we consider them normal variants of no relevance except for ruling out neoplasms mimicking these minor abnormalities (Tscholl et al. [27]).
Clinical relevance of calcaneal cysts depends upon size (Pogoda et al. [28]). It is of interest that calcaneal cysts and calcaneal lipomas may be a single entity and a pathogeneic continuity may exist (Malghem et al. [29]).
The incidentally found case of the osteofibrous dysplasia with rhabdoid elements and spontaneous resolution has been published recently (Exner et al. [30]).
5. Drawbacks and Limitations of This Study
Follow-up of the patients in our observational group is incomplete and with an average of 4.1 years short for lesions, which only at very long term, probably decades, may change their activity.
Patients not followed by the authors usually stay in the initial medical setting; therefore they most likely would have presented to the referring orthopaedist or to our group in case of symptoms or imaging changes of their bone lesion.
Furthermore, the diagnoses were almost exclusively based on imaging findings alone.
Other lesions that typically present incidentally as e.g. intraosseous hemangioma were not encountered in this series but need to be recognized.
6. Summary and Conclusions
Our findings agree with those of Ahmed et al. [3], Patel et al. [1], and Davies et al. [29] that asymptomatic patients with long bone enchondromas less than 5 cm longitudinal extension with no endosteal scalloping do not need systematic imaging follow-up and can be discharged after explanation of the diagnosis and instruction to seek medical attention in case of any change, development of discomfort or increasing pain.
The lesions larger than 5 cm have remained stable in our patients; however, follow-up is too short to exclude progression into chondrosarcoma grade II or even grade III at longer intervals. Therefore we cannot provide data on the time interval needed to develop dedifferentiation. Until more data are available it may therefore be cautious to repeat imaging. This, however, should be done at rather longer time intervals; 5-year intervals may be reasonable as with shorter intervals patients not seeing definitive progression would become reluctant to submit to further examinations creating unnecessary concerns and last but not least costs. We hope that systematic follow-up data will add to the scientifically based care of patients with incidentally found enchondromas.
Ethical Approval
The study was approved by the institutional review boards.
Informed Consent
Informed consent was obtained from all patients.
Authors’ Contribution
The first author collected the data, all authors contributed equally to the evaluation and interpretation of images, and finalizing the manuscript.