European Journal of Radiology

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1 European Journal of Radiology 77 (2011) 6 12 Contents lists available at ScienceDirect European Journal of Radiology journal homepage: When should we biopsy a solitary central cartilaginous tumor of long bones? Literature review and management proposal Caroline Parlier-Cuau a,, Valerie Bousson a, Christian M. Ogilvie b, Richard D. Lackman b, Jean-Denis Laredo a,c a Department of Radiologie Ostéo-Articulaire, Hôpital Lariboisière, Assistance Publique-Hôpitaux de Paris (AP-HP), Faculté de Médecine Denis Diderot, Université Paris 7, Paris, France b Department of Orthopedic Surgery, Pennsylvania Hospital, 800 Spruce Street, Philadelphia, PA 19107, USA c Department of Musculoskeletal Radiology, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA article info abstract Article history: Received 14 June 2010 Accepted 15 June 2010 Keywords: Enchodroma CT MRI Guidelines Differentiation between benign and low-grade malignant cartilaginous tumors is a radiological and pathological challenge. Based on a literature review, we propose the following guidelines for the management of a solitary central cartilaginous tumor of long bones distinguishing three situations: 1. The tumor is considered to be aggressive and requires surgery if one of the following criteria is present: cortical destruction, Moth-eaten or permeative osteolysis, spontaneous pathologic fracture, periosteal reaction, edema surrounding the tumor on MR images, and soft tissue mass. Tumor biopsy followed by complete intralesional treatment is indicated. 2. The tumor is classified as active if two of the following active criteria are present: pain related to the tumor, endosteal scalloping superior to two-thirds of the cortical thickness, extent of endosteal scalloping superior to two-thirds of the lesion length, cortical thickening and enlargement of the medullary cavity. Tumor biopsy or excision is indicated. 3. The tumor is classified as possibly active if one of the previous active criteria is present. In such cases, bone scintigraphy and dynamic-enhanced MR imaging should be obtained. Radionuclide uptake superior to the anterior iliac crest at bone scintigraphy and early and exponential enhancement at dynamic-enhanced MR are considered as two additional active criteria. After these two examinations, if only one criterion is still present, the lesion can be regarded as possibly quiescent, and the following monitoring is suggested: first follow-up at three to six months and then once a year. Otherwise, if two or more active criteria are present, biopsy is recommended. 4. The tumor is considered quiescent and does not require surgery if no active or aggressive criterion is present. A radiological follow-up can be proposed Elsevier Ireland Ltd. All rights reserved. Differentiation between solitary enchondromas (Chs), lowgrade central chondrosarcomas (CSs) and high-grade central chondrosarcomas (CSs) is a radiological and pathological challenge. In hands and feet, CSs are very uncommon, and a Ch can be confidently diagnosed on its radiological appearance in the very large majority of cases and thus will not require a biopsy. On the contrary, in the axial skeleton, CSs are more frequent than Chs [1] and a biopsy is almost always indicated in this location. In long bones, Corresponding author at: Service de Radiologie Ostéo-Articulaire, Hôpital Lariboisière, AP-HP, Faculté R Diderot Paris VII, 2 rue Ambroise Paré, Paris, France. Tel.: ; fax: address: Caroline.parlier@lrb.aphp.fr (C. Parlier-Cuau). this differentiation is particularly critical since a small image suggestive of Ch is found incidentally in as much as three percent of routine knee MR examinations [2], while CSs are not uncommon. Not all central cartilaginous tumors of the long bones should be biopsied since the vast majority will remain quiescent throughout patients life. It is therefore critical to be able to select which cartilaginous lesions of long bones need to be biopsied. Several articles attempted to identify the differential radiological findings between Chs and CSs [3 14]. However, no management guidelines have been given in the literature, and there is a need for management standardization. Therefore, based on a literature review, we selected the clinical and radiological criteria which were the most likely to be indicative of an active or aggressive central cartilaginous tumor and propose guidelines to decide which solitary central X/$ see front matter 2010 Elsevier Ireland Ltd. All rights reserved. doi: /j.ejrad

2 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) chondromatous tumors of long bones should undergo a biopsy, knowing that the present proposals need clinical validation. 1. Central chondromas versus chondrosarcomas: literature review (Tables 1 and 2) 1.1. Clinical criteria (Tables 1 and 2) Age CSs predominate between 40 and 60 years with an average age of 46 (extremes: 5 82 years) [15,16], whereas the average age in Chs is 40 years [12]. There is a slight male predominance in CSs (55 61%) [6,10,12], and no sex predominance in Chs Location The femur is the most commonly affected bone in both lesions [12]. However, a location to the proximal part of the femur is more in favor of a CS [12]. On the other hand, the proximal metaphysis of the humerus and tibia, as well as the distal metaphysis of the femur, point statistically towards a Ch [12] Clinical symptoms Pain is the most common symptom and is almost constant in the case of CSs (81% [15] to 95% (p = 0.02) [12]), but it is also noted in 34% of the cases of Chs [8,12,17]. Pain characteristics, however, differ slightly between the two tumors. The pain typically lasts longer and grows in intensity in CSs [1,6]. Pain which is genuinely linked to a cartilaginous tumor and is not explained by a fracture or articular derangement is suggestive of CS Radiographic and CT criteria (Table 1) Many studies focused on the discriminating power of radiographic and CT scan findings to differentiate Chs from CSs [6 8,11 14] (Table 1). Grade 1 CSs are more voluminous than Chs. Geirnaerdt et al. set a 5 cm-limit to distinguish between both lesions [8], whereas Kendell et al. put a 4 cm-limit [11]. However, when Chs involving the extremities are excluded, the difference is less marked [8]. In the series of Murphey et al., the average tumor size was 5 cm for Chs and 8 cm for CSs [12]. For most authors, a tumor size in excess of 6 cm is suspicious for CSs [6,8,10,12,14,18]. Tumor size, however, has a limited value, especially in long bones, where there is wide overlap in size range between Chs and CSs. Radiographs are of limited value for the differentiation of Chs from Grade 1 CSs [8,11] due to the high inter-observer variability of radiographic findings [8]. Geirnaerdt et al. found that only two radiographic criteria allowed significant discrimination between Chs and CSs, namely ill-defined margins involving 25% or more of the lesion circumference (67% of CSs and 37% of Chs, p = 0.004), and lobulated lesion contours (72% of CS and 43% of Ch, p = 0.009) [8]. In the same study, pa CS could be diagnosed with a likelihood of more than 90% when four criteria (ill-defined margins, lobulated contours, pop-corn calcifications and endosteal scalloping) were present altogether. However, this combination was encountered in less than 6% of the cases in the Geirnaerdt et al. study population [8]. CT scans allow a more reliable radiological analysis of central cartilaginous tumors than radiographs (Figs. 1 3). Endosteal scalloping of the bone cortex at CT-scan has been classified by Murphey et al. both by depth and length extent into the cortex [12]. They found that endosteal scalloping depth was particularly discriminant since 90% of CSs and only 10% of Chs demonstrated a scalloping of more than two-thirds of the cortical thickness on transverse CT scan images [12] (Figs. 2 4). Lesions with this finding were 77 times Table 1 Literature review: radiographic and CT criteria. Geirnaerdt et al. [8] Murphey et al. [12] Kendell et al. [11] P-value n =39 P-value Enchondroma n =54 n =95 P-value Enchondroma n =92 n =43 Enchondroma n =35 Grade 1 n = 36Grade 2 n =3 Grade 1 n = 43 Grade 1 n = 32Grade 2 n = 29Grade 3 n =31 Clinical symptoms 13 (37%) 25 (58%) % 95% X-ray or CT Size (cm) 1 20 (3.5) 2 14 (M 5) < (M 5) 3 26 (M 8) (M 3.6) 2 14 (M 5.1) O.0023 Endosteal scalloping > 2/3 4 (11%) 44 (90%) < (24%) 3 (21%) NS of cortical thickness Endosteal scalloping > 2/3 11 (34%) 37 (79%) < NS of lesion extent Widening of the medullary 17 (49%) 22 (51%) (21%) 26 (53%) < (54%) 27 (69%) cavity Hyperostosis 4 (11%) 5 (12%) (17%) 45 (47%) < (4%) 7 (18%) Soft tissue mass 4 (11%) 7 (16%) (3%) 25 (76%) < (0%) 8 (20%) Cortical disruption 7 (20%) 13 (30%) (8%) 43 (88%) < (15%) 14 (64%) O.0133 Periosteal reaction 16 (46%) 21 (49%) (21%) 23 (47%) < (2%) 7 (18%) Pathologic fracture 5 (5%) 26 (27%) (9%) 5 (13%) Scintigraphy Uptake >anterior Iliac crest 14 (21%) 42 (82%) < Heterogeneous uptake 20 (30%) 32 (63%) M: mean; NS: not specified.

3 8 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) 6 12 Table 2 Literature review: MR criteria. Aoki et al. [3] De Beuckeleer et al. [5] Janzen et al. [10] Murphey et al. [12] Geirnaerdt et al. [9] Ch n =3 CSn =5 P-value Ch n =16 CSn =23 P-value Ch n =10 CSn =13 P-value Ch n =92 CSn =95 P-value Ch n =8 CSn =18 P-value Grade 1 n = 7Grade 2 n = 9Grade 3 n =2 Grade 1 n = 32Grade 2 n = 29Grade 3 n =31 Grade 2 n = 8Grade 3 n =5 Grades 1 and 2 n = 18Grade 3 n =5 Number of cases Grade 1 n = 3Grade 2 n = 1Grade 3 n =1 Clinical symptoms 79% 95% Size (cm) 3 8 (M 5) 4 17 (M 8) MRI Soft tissue mass 0 8 (62%)Grade n = 3Grade3 n =5 NS Cortical disruption 0 8 (62%)Grade2 n = 4Grade3 n =4 Small foci of high signal on T1WI 65% 35% Low SI septa on T2 WI 9 (56%) 15 (65%) NS Central or peripheral gadolinium 3 5 NS 10/13 (77%) NS NS NS enhancement Septal gadolinium enhancement 3 5 NS 3/13 (23%) 14/18 (81%) NS NS NS Early enhancement on dynamic 0 (0%) 16 (89%)Grade <0.001 gadolinium-enhanced MRI 1 n = 7Grade 2 n = 7Grade 3 n =2 0 (0%) 11 (61%)Grade < n = 4Grade 2 n = 5Grade 3 n =2 Exponential curve on dynamic gadolinium-enhanced MRI Peri-tumoral edema on T2 WI 0 13 (100%) < NS: not specified. Fig. 1. Grade 1 chondrosarcoma of the left humerus in a 42-year-old female with shoulder pain. (a) Antero-posterior radiograph of the left shoulder in external rotation shows a cartilaginous lesion with arcs and rings pattern. (b) CT-scan of the proximal humerus shows focal postero-lateral cortical destruction and deep endosteal scalloping superior to two-thirds of cortical thickness posteriorly (arrow). (c) Delayed bone scintigram shows heterogeneous and uptake similar to the anterior iliac crest in the lateral portion of the lesion (arrow). (d) On Axial T1-Weighted MR image, the lobulated lesion exhibits intermediate signal intensity. (e) On STIR MR image lesion has high-signal intensity. Focal soft-tissue high-signal intensity is seen at the site of cortical disruption (arrows). (f) Fat-supressed, gadolinium-enhanced T1-Weighted MR image shows septal and peripheral enhancement pattern and enhancement of the infra-spinatus. (g) Axial fast contrast-enhanced MR image shows the different regions of interest, one (red circle) is plotted in the region with the earliest enhancing lesional tissue. (h) In the time signal intensity diagram, the vertical axis represents signal intensity in arbitrary unit and the horizontal axis represents time in minutes. Yellow curve represents arterial enhancement and red curve shows early and exponential enhancement depicted in the lateral part of the lesion. Two active criteria are present in this case: endosteal scalloping superior to twothirds of the cortical thickness (arrow) on CT-scan image and early and exponential enhancement on dynamic-enhanced MR imaging (red curve). A surgical biopsy reveals a Grade1 CS and a complete intralesional treatment was performed.

4 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) Fig. 2. Cartilaginous tumor in the distal femur in a 33-year-old male. (a) Anteroposterior radiograph of the femur shows a central cartilaginous lesion. (b) CT scan reveals punctuate and rings calcifications with no abnormality of the cortex. (c) The lesion is lobulated (arrows) and has low-signal intensity on axial T1-Weighted MR image and (d) high-signal intensity on STIR MR image. (e) Axial and sagittal (f) fat-supressed, gadolinium-enhanced T1-Weighted MR image shows peripheral enhancement pattern (arrowheads). No active or aggressive criterion is present. Radiological follow-up was proposed. more likely to be malignant [12]. Such areas of deep cortical scalloping probably represent regions of active growth and may involve only small foci within the entire chondroid lesion [6]. If a biopsy is to be carried out, it must cover these areas [19]. When an endosteal scalloping has perforated the cortex (Fig. 1), the probability of a CS is even greater (88% of CSs compared to 8% of Chs, odd ratio 86) and even more if the tumor has spread into the soft tissues [12] (Fig. 5). The longitudinal extent of the cortical scalloping was also studied by Murphey et al. [12]. Longitudinal extent of the cortical scalloping to over two-thirds of the lesion length also pointed, at a lesser degree, towards a CS (79% of CSs and 34% of Chs, odd ratio 7) [12] (Fig. 4). In addition, Murphey et al. suggested that the presence of cortical remodelling with widening of the medullary cavity was a sign of tumoral activity, which was more frequently associated with CSs (Fig. 4) than Chs (53% of CSs compared to 23% of Chs, p < ) [12]. Presence of a periosteal reaction (Fig. 4) and cortical thickening were also more frequently observed in CSs (47% for both signs in CSs versus 21% and 17% respectively in Chs) [12]. Kendell et al. reported similar results [11]. We found, from our clinical experience, that criteria concerning the cortex in long bone Fig. 3. Cartilaginous tumor in 45-year-old female with no pain. (a,b) Anteroposterior radiograph (a) and CT-scan (b) of proximal fibula shows focal and deep endosteal scalloping superior to the two-thirds of the cortical thickness at the lateral aspect of the lesion (arrows). (c) On sagittal T1-Weighted image, the lesion shows low-signal intensity and deep endosteal scalloping (d) coronal STIR MR image shows lobulated contours and hyper intense signal of the lesion. One active criterion is present, a bone scintigraphy and dynamic gadolinium-enhanced MR imaging are obtained. (d) Bone scintigraphy shows a faint uptake, lesser than that of the AIC on delayed images. (e) Axial fast contrast-enhanced MR image shows the different regions of interest, (f) in the time signal intensity diagram. White curve represents arterial enhancement and dot curve cartilagineous tumor: no early and exponential enhancement on dynamic-enhanced MR images. At the end of the examination, there is still only one active criterion present and a careful radiological monitoring is proposed.

5 10 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) 6 12 ings were not differential variables (p = and 0.53 respectively) both at CT and MR imaging [12] MR criteria [1,3,7,10,17,18,20,22] (Table 2) Fig. 4. Grade I chondrosarcoma of the distal femur in a 45-year-old male with knee pain. (a) Lateral radiograph of femur shows widening of the medullar cavity (arrows) and focal periosteal reaction along the anterior cortex (arrowheads). (b) Coronal T1-Weighted image reveals a marked expanded femoral contour and deep endosteal scalloping (arrows). (c) Coronal gadolinium-enhanced T1-Weighted MR image shows nodular enhancement pattern (star)) (d) STIR image shows highsignal intensity and deep endosteal scalloping extending over more than two-thirds of the lesion. The Ch is considered active and three active criteria are present: pain related to the tumor, widening of the cavity and endosteal scalloping superior to the two-thirds of the cortical thickness. Surgical biopsy confirmed the Grade 1 CS and was followed by a complete intralesional treatment. diaphyses cannot be applied straightforward to the metaphyseal region where the cortex is very thin and slightly irregular, particularly at the medial cortex of the upper extremity of the humerus. In such cases, comparison with the healthy controlateral side is useful. Presence of a soft tissue mass is considered as almost pathognomonic for malignancy [1,10,12] (Fig. 5). This sign, however, is most often encountered in high-grade than in low-grade CSs [1,10] (Fig. 5). In Grade 1 CSs, a soft-tissue mass is seen in only 16% of patients [8]. Therefore, the absence of tumor extension into the soft-tissue does not exclude a central Grade 1 CS. CT-scan allows a precise analysis of the presence and type of tumor calcifications. However, Murphey et al. found these find- Concerning signal intensity abnormalities, the presence of intralesional foci of high-signal intensity on T1-Weighted images has been more frequently observed in Chs (65%) (Fig. 4) than in CSs (35%) (p <.024) [6,12] and is probably related to the lobular growth of Chs, which leaves intervening residual areas of normal yellow bone marrow, in contrast to the solid replacement of marrow fat described in CSs [21]. Value of the presence of low-signal intensity septa on T2- Weighted MR images within the tumor (Fig. 1) is controversial. De Beuckeleer et al. reported that 3 out of 13 Chs and 14 out of 18 CSs showed septal or ring-and-arc enhancement on nondynamic gadolinium-enhanced MR sequences with a sensitivity of 92% and a specificity of 76% [5]. Whereas, in three other series, septal, peripheral and nodular enhancement were seen in Chs as well as low-grade CSs without statistical difference [3,9,12] (Figs. 1 and 4). In a small series comparing 10 Chs and 13 CSs, Janzen et al. reported that peri-tumoral edema was visible on Short Tau Inversion Recovery (STIR) images in CSs only [10]. However, no Grade 1 CS was included in this series, and therefore this criterion may not be useful to distinguish Chs from Grade 1 CSs. Finally, results of studies dealing with signal intensity abnormalities on nonenhanced and non-dynamic gadolinium-enhanced MR imaging in order to differentiate Chs from CSs are controversial. Dynamic gadolinium-enhanced MR sequences are currently available on most recent MR units [23,24] and have already proved to be useful for the differentiation of benign from malignant tumors in bone [24] and soft tissue [23]. These MR sequences may also have the potential to help in the differentiation between Chs and CSs [9]. Geinaerdt et al. found that the combination of an early (enhancement beginning within 10 s after the start of arterial enhancement) and exponential enhancement (fast enhancement increase parallel to early arterial enhancement, followed by an early maximum plateau or by a slight increase in enhancement) on dynamic gadolinium-enhanced MR sequences was statistically more frequent in CSs (p <.001) [9] (Fig. 1). Early and exponential enhancement was seen in 11 out of the 18 CSs with a sensitivity of 61% and a specificity of 95% for CSs [9]. Absence of or delayed enhancement (tumoral enhancement which occurred after 10 s) excluded CS in this study [9]. These findings, however, have to be confirmed by further studies Bone scintigraphy criteria [12] Bone scintigraphy may be useful to the differential diagnosis between Chs and CSs [12]. Radionuclide uptake is present in both types of tumors (Figs. 1 and 2) but the level of increased uptake may be different. In order to be able to use bone scans performed on different imaging units, Murphey et al. proposed to compare on whole-body images the radionuclide uptake of the tumor to the uptake of the anterior iliac crest (AIC). They found that tumor radionuclide uptake was superior to that of the AIC in 82% of CSs with a heterogeneous aspect in 63% of cases (Fig. 1) and that, conversely, Chs showed a radionuclide uptake which was lower or equal to that of the AIC in 79% of the cases (Fig. 2) with a homogeneous aspect in 70% of the cases [12] Proposed classification of the radiological criteria (Table 3) Fig. 5. Grade 2 chondrosarcoma of the proximal femur in a 67 year-old man. (a) Two aggressive criteria are present. Axial CT scan image shows a cortical destruction (curved arrows). (b) Axial T2-Weighted image reveals a soft tissue mass (arrow). According to this literature review, radiological findings can be classified into aggressive and active (Table 3). Reported studies which analyzed such findings have a number of limitations,

6 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) Table 3 Classification of radiological findings which may be useful to the management decision. Active Pain related to the lesion Endosteal scalloping > 2/3 of the cortical thickness Extent of endosteal scalloping along > 2/3 of the lesion length Cortical thickening or hyperostosis Cortical remodelling with enlargement of the diameter of the medullary cavity Delayed bone scintigram showing an intense uptake greater than that of the AIC in the absence of fracture Early and exponential enhancement on dynamic gadolinium-enhanced MR sequences Aggressive Pathologic fracture arising with minimal trauma Pluri-lamellar or spiculated periosteal reaction Moth-eaten or permeative osteolysis Cortical destruction Presence of a soft tissue mass including their retrospective format, the small numbers of cases, and selection bias. An additional limitation to most of these studies is the inclusion into a single category of Grades 1 3 CSs [10] which require completely different surgical management. In addition, an inherent difficulty in studies comparing Chs and CSs is the inability to distinguish accurately at pathological examination a Grade 1 CS from an active Ch. Aggressive criteria suggestive of a high-grade (Grade 2 or 3) CS disrupting the anatomical planes are: pathological fracture arising with minimal trauma, pluri-lamellar or spiculated periosteal reaction, moth-eaten or permeative osteolysis, cortical destruction, and presence of a soft tissue mass. Presence of a peritumoral edema on STIR MR images should probably be added to this list in the future if further studies confirm this sign is associated with aggressive CSs. When such signs are lacking, a further analysis of radiologic findings should look for active criteria which reflect that the tumor has some effects on the surrounding tissue. They may be encountered both in active Chs and in Grade 1 CSs. These findings are the following: pain related to the tumor, endosteal scalloping involving more than two-thirds of the cortical thickness in the diaphysis of a long bone, or more than two-thirds of its length, cortical thickening or hyperostosis, cortical remodelling with enlargement of the diameter of the medullar cavity, an intense uptake greater than that of the AIC on delayed bone scintigraphy in the absence of fracture, and early and exponential enhancement on dynamic gadoliniumenhanced MR imaging. 2. Proposal for the management of a central cartilaginous tumor of long bones (Table 4) First line radiological examinations should include radiographs [25] and either MRI or CT-scan which both allow radiological analysis of cartilaginous tumors. Based on this first radiological evaluation, four situations can be differentiated which lead to different types of management: Table 4 Management of a solitary central cartilaginous tumor of long bones. Management of solitary cartilaginous tumor of long bones Initial examination: radiographs and CT or MRI 1/ One aggressive criteria present 2/ Two or more active criteria present 3/ One active criterion present 4/ No active or aggressive criteria present 1 One aggressive criterion is present: The Ch is considered aggressive (Fig. 5). In such cases, a high-grade CS is suspected and biopsy is indicated [6,19]. The biopsy should be directed toward the most aggressive part of the tumor (e.g. extraosseous soft tissue mass or permeative destruction of bone) since such tumors may be heterogeneous in grade. If the biopsy reveals low-grade cartilage, yet the tumor has several aggressive features, consideration should be given for performing another biopsy in a different part of the tumor before proceeding with an intralesional surgery. Simi- scintigraphy and dynamic-enhanced MR imaging should be obtained in search for additional active criteria: - Radionuclide uptake > to anterior iliac crest - Early and exponential enhancement on dynamic- enhanced MR imaging Excisional biopsy followed by complete intralesional treatment Two or more active criteria One active criterion First follow-up imaging after 3 to 6 months then once a year Change at follow-up

7 12 C. Parlier-Cuau et al. / European Journal of Radiology 77 (2011) 6 12 larly, if non-solid cartilage is encountered during an intralesional surgery, then one should stop and get specimens for additional pathologic analysis. Grades 2 and 3 CSs are treated with wide resection. 2 Two or more criteria of active tumor are present: The tumor should be regarded as potentially active and may correspond to an active Ch or to a CS as well. Tumor biopsy or excision is indicated. When not too damaging, excisional biopsy or complete intralesional surgery is preferred to a simple biopsy due to the frequent heterogeneity of cartilaginous tumors. In addition, if the cartilage appears solid and not myxoid at macroscopic examination during biopsy, or if the frozen section shows low-grade cartilage, then complete removal of the lesion may be considered, provided there are no signs of a Grade 2 or higher tumor. Otherwise, the biopsy should be directed toward the most active part of the lesion. 3 Only one criterion of active tumor is present on radiographs and CT scans or conventional MRI (Fig. 3). We suggest that both bone scintigraphy and dynamic gadolinium-enhanced MR imaging should be obtained in such cases in order to look for additional criteria of tumor activity namely an intense uptake greater than the AIC at bone scintigraphy and the presence of an early and exponential enhancement on dynamic gadolinium-enhanced MR sequences (Figs. 1 and 4). If none of these two additional radiological evaluations show arguments for an active tumor, we suggest that the lesion can then be regarded as probably quiescent and that abstention together with a careful radiological monitoring can be still proposed similarly to the situation 4 discussed below. Conversely, in cases where dynamic gadolinium-enhanced MR sequences or bone scintigraphy show an additional sign of activity (Figs. 1 and 4) the tumor should be regarded as probably active and managed as in situation 2. 4 No aggressive or active criteria are present: The lesion can be considered as a quiescent Ch (Fig. 2). In most of these cases, the lesion is discovered incidentally on a knee or shoulder MRI examination performed for joint derangement [2]. The tumor usually does not reach the inner cortex with persistence of fatty marrow between the tumor and the cortical endosteum. In cases where the tumor reaches the inner cortex, endosteal scalloping is absent or minimal. When performed, bone scintigraphy shows a faint uptake, lesser than that of the AIC on delayed images. In such cases, management may be limited to a clinical and radiological follow-up but the importance of this follow-up should be carefully explained to the patient. In such situations, our team is used to schedule the first radiological follow-up examination three to six months after the initial evaluation to insure that the lesion is quiescent and then once a year in the absence of any change. Choice of the radiological modality used for the follow-up examination (radiographs, CT or MRI) will depend on lesion location and type of initial examination. CT scan or MRI is recommended in light of the wide variations in inter-observer analysis on radiographs [8]. Any radiological change at follow-up or onset of clinical symptoms related to the tumor should lead to a new complete radiological evaluation and a tumor biopsy if the change is confirmed. The duration of the follow-up that should be carried out is unknown. Brien et al. recommended that solitary Chs of long bones should be followed for at least two decades if detected after age 25 [6]. 3. 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