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Prevalence and characteristics of benign cartilaginous tumours of the knee joint as identified on MRI scans

Prevalence and characteristics of benign cartilaginous tumours of the knee joint as identified on... Background Enchondromas (EC) and atypical cartilaginous tumours (ACT ) of the knee joint represent benign/ intermediate chondromatous neoplasms of the bone that are most commonly discovered incidentally. Based on small to intermediate-sized cohorts, the prevalence of cartilaginous tumours of the knee as visible in MRI is estimated at 0.2–2.9%. This study aimed at verifying/challenging these numbers via retrospective examination of a larger, uniform patient cohort. Methods Between 01.01.2007 and 01.03.2020, 44,762 patients had received an MRI of the knee for any indication at a radiologic centre. Of these, 697 patients presented with MRI reports positive for cartilaginous lesions. In a three-step workflow, 46 patients were excluded by a trained co-author, a radiologist and an orthopaedic oncologist, as wrongly being diagnosed for a cartilage tumour. Results Of 44,762 patients, 651 presented with at least one EC/ACT indicating a prevalence of 1.45% for benign/ intermediate cartilaginous tumours of the knee joint (EC: 1.4%; ACTs: 0.05%). As 21 patients showed 2 chondromatous lesions, altogether 672 tumours (650 ECs [96.7%] and 22 ACTs [3.3%]) could be analysed in terms of tumour characteristics: With a mean size of 1.6 ± 1.1 cm, most lesions were located in the distal femur (72.9%), in the metaphysis of the respective bone (58.9%) and centrally in the medullary canal (57.4%). Conclusions This study revealed an overall prevalence of 1.45% for cartilage lesions around the knee joint. Whilst a constant increase in prevalence was found for ECs over 13.2 years, prevalence remained constant for ACTs. Keywords Enchondroma, Atypical cartilaginous tumour, Prevalence, Knee joint, MRI *Correspondence: Maria Anna Smolle maria.smolle@medunigraz.at Department of Orthopaedics and Trauma, Medical University of Graz, Graz, Austria Diagnostikum Graz, Graz, Austria © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Woltsche et al. Cancer Imaging (2023) 23:50 Page 2 of 9 Background Tumor” (cartilaginous tumour), “chondrogene Läsion” Enchondromas (ECs) and atypical cartilaginous tumours (chondrogenic lesion), “chondrogener Tumor” (chon- (ACTs, formerly known as chondrosarcoma grade 1) are drogenic tumour), “Chondrosarkom” (chondrosarcoma), cartilaginous neoplasms located in the medullary canal “ACT - atypischer chondromatöser Tumor“ (atypical [1–4]. While ECs represent the most common intramed- chondromatous tumour), “atypische chondromatöse ullary benign cartilaginous lesion [1, 2], ACTs constitute Läsion“ (atypical chondromatous lesion). an intermediate neoplasm that is often hard to distin- Altogether, 697 patients’ MRI reports were positive for guish from EC [2, 3]. However, distinction between these at least one search term and were subsequently analysed lesions is of great importance, as ACTs – on the contrary in further detail (Fig.  1). Of these, 21 patients had to be to ECs – require surgical treatment [3, 4]. Certain imag- excluded due to the following reasons: In 11 patients, ing features allow some assessment of the tumours’ dig- reason for referral had been a suspected cartilaginous nity: large lesion size, as well as presence of periosteal tumour but MRI could not confirm this tentative diagno - reaction, endosteal scalloping or perilesional edema can sis; 3 patients had MRI reports containing not only find - help differentiate ACT from EC [ 2, 5]. The latter are most ings of MRIs of the knee but also of other body regions, often found in the short bones of the hand (40–65%), in whom they had been diagnosed with a cartilage lesion; whilst long bones (femur, humerus, tibia) are the second 2 patients were initially suspected to have an enchon- most common location for EC, accounting for 25% of droma, yet follow-up MRIs led to a change of primary cases [6, 7]. diagnosis; 5 patients had undergone surgical removal of ECs typically present clinically silent, with large lesions the cartilaginous lesion prior to index imaging. eventually causing pain or – especially in short bones – Reports of the remaining 676 patients were re-exam- pathologic fractures [3, 5]. Therefore, this tumour is most ined together with related MRI scans, and a definitive commonly found incidentally during routine clinical radiologic diagnosis of cartilaginous tumours was con- imaging (X-ray, CT [computed tomography], MRI [mag- firmed in 635 patients. However, 41 patients had incon - netic resonance imaging]). Consequently, the true preva- clusive reports and images. Therefore, the advice of a lence of EC remains uncertain [3, 7]. Thus far, five studies senior radiologist was sought for these cases. Thereafter, have analysed the prevalence of benign cartilaginous 20 more patients were excluded, as they did not show lesions around the knee based on MRI, reaching figures typical features of EC/ACT, resulting in 656 patients ulti- between 0.2 and 2.9% [2, 3, 8–10]. mately eligible. As all five studies were based on small to intermediate- MRI-based differentiation into EC (Fig.  2) and ACT sized cohorts, this study aimed at verifying these num- (Fig.  3) was made based on tumour characteristics sus- bers via retrospective examination of a larger, uniform picious of aggressive behavior as proposed by Mulli- patient cohort with MRI scans of the knee. gan et al. [5], Murphey et al. [4], van de Sande et al. [11] and Douis et al. [12], i.e. tumour size > 4.9  cm, periosteal Methods reaction, perilesional edema or deep endosteal scallop- Study design and study population ing involving ≥ 2/3 of cortical thickness. With either one The current retrospective study was performed with data of these features being positive, chondrogenic lesions deriving from a private radiologic centre, performing – were classified as ACT. All tumours exhibiting at least apart from numerous other imaging modalities – MRI one of these features were thoroughly examined by an scans of all body sites. The local medical ethics com - experienced orthopedic oncologist, who excluded 5 mittee has approved the study (33–630 ex 20/21) that more patients due to diagnosis of bone infarction (n = 3), involved patients having received an MRI of the knee for postoperative changes (n = 1) and intraosseous ganglion any indication between 01.01.2007 and 01.03.2020. Dur- (n = 1). ing that time, 44,762 patients had undergone at least one Overall, 651 patients had a cartilaginous tumour, with knee MRI scan. Of these, 5182 had undergone MRI scans 21 patients presenting with 2 cartilaginous lesions at the of both knee joints, resulting in a total of 24,125 and same time, resulting in 672 cases of EC/ACT. 25,819 MRI scans of the left and right knee, respectively. All MRI reports of the knee were searched for at least Lesion analysis one of the following terms by one of the co-authors (J.W.) MRI was considered positive for a cartilaginous tumour who had performed an extensive study of literature and on identification of a smooth or lobulated lesion that pre - had received intensive training on imaging features of sented itself as a focal geographic area within the bone cartilage lesions before data acquisition: “Enchondrom” marrow, showing low signal intensity on proton-den- (enchondroma), “kartilaginäre Läsion” (cartilaginous sity-weighted and on T1-weighted images and high sig- lesion), “cartilaginäre Läsion” (cartilaginous lesion), “kar- nal intensity on proton-density fat-suppressed images. tilaginärer Tumor” (cartilaginous tumour), “cartilaginärer Lesions positive for these characteristics but strictly Woltsche et al. Cancer Imaging (2023) 23:50 Page 3 of 9 Fig. 1 Flow chart representing the filtering of patients with a cartilaginous tumour subchondral in location had to be excluded, as they MRI most likely represent different entities such as subchon - MRI examinations were performed on two different 3T dral cysts, intraosseous ganglia, subchondral edema or MRI systems (Siemens Magnetom Skyra/Siemens Magne- contusion. tom Vida; both Siemens Healthcare Diagnostics GmbH, Apart from patient gender and age, the following Austria) with a 15/18-channel knee coil. Sequences tumour-specific features were ascertained: lesion size acquired were (1) coronal proton density (PD) with fat (maximal tumour diameter in cm), lesion site (femur, suppression (FS) (field of view (VF) 160/140 mm; Matrix tibia, fibula, patella), tumour location (eccentric or cen - (M) 307 × 384/307 × 384; repetition time (TR) 3000/3200 tral; epiphyseal, epimetaphyseal, metaphyseal, metadi- ms; echo time (TE) 34/25 ms; slice thickness (ST) 3/3 aphyseal, diaphyseal), endosteal scalloping, perilesional mm; interslice gap (IG) 0.6/0.6  mm); (2) transversal edema and periosteal reaction. Furthermore, indication PD with FS (VF 160/150 mm; M 307 × 384/307 × 384; for MRI (tumour associated symptoms or follow-up TR 5460/4110 ms; TE 37/35 ms; ST 2.5-3/3 mm; IG examinations; no tumour related indication; no docu- 0.6/0.6 mm); (3) sagittal PD with FS (VF 160/140 mm; M mented indication) and whether the patients had under- 307 × 384/307 × 384; TR 2920/2920 ms; TE 34/34 ms; ST gone dynamic contrast MRI was ascertained. 3/3 mm; IG 0.6/0.6  mm); (4) coronal T1 weighted turbo spin echo (TSE) (VF 160/140 mm; M 346 × 384/290 × 484; Woltsche et al. Cancer Imaging (2023) 23:50 Page 4 of 9 Fig. 2 EC of the right tibia: (A) proton density, fat suppression, coronal, turbo spin echo; (B) proton density, fat suppression, transversal, turbo spin echo; (C) proton density, fat suppression, sagittal, turbo spin echo; (D) t1, coronal, turbo spin echo (year of MRI: 2016) TR 690/690 ms; TE 11/19 ms; ST 3/3 mm; IG 0.6/0.6 mm; calculated based on the diagnosis of a benign cartilagi- flip angle (FA) 180°/150°). nous lesion per patient, and not based on the number of Gd-DTPA (dose 2 ml/kg body weight) via venous cartilage lesions found in total. In line with this, patients access was administered in 77 of 651 patients (81 of without ECs/ACTs undergoing MRI scans of both knee 672 tumours), followed by an MRI examination with joints during the defined period were counted once only the sequence “(4) coronal T1 weighted turbo spin echo” for calculation of prevalence. Normally and non-nor- that was subtracted from the native T1 sequence. Addi- mally distributed variables were given as means and cor- tionally, T1 sequences with fat suppression in different responding standard deviations, as well as medians and dimensions were recorded. corresponding interquartile ranges (IQR), respectively. Fisher’s exact test and t-test were used to assess differ - Statistical analysis ences in binary (or ordinary) and continuous variables, Statistical analyses were carried out with Stata Version respectively, depending on radiological diagnosis. A 16.1 for Mac (StataCorp, College Station, Texas, US). p-value of < 0.05 was considered statistically significant. Patient demographics were summarized for based on the total number of patients with cartilaginous lesions. Tumour demographics were summarized from the total number of lesions found in patients. Prevalence was Woltsche et al. Cancer Imaging (2023) 23:50 Page 5 of 9 Fig. 3 ACT of the left femur: (A) proton density, fat suppression, coronal, turbo spin echo; (B) proton density, fat suppression, transversal, turbo spin echo; (C) proton density, fat suppression, sagittal, turbo spin echo; (D) t1, coronal, turbo spin echo (year of MRI: 2016) Results found both in the left and right knee, amounting to 672 Prevalence of benign cartilaginous lesions tumours in total. Mean age of patients with EC/ACT was Between 01.01.07 and 01.03.2020, the prevalence 52.1 ± 13.1 years, and 48.4% were males (n = 315). The rea - of benign cartilaginous lesions (i.e. ECs and ACTs) son for referral to MRI was suspected EC based on pre- amounted to 1.45%. In detail, the separate prevalence for ceding imaging in 79 cases (12.2%), a suspected pathology ECs and ACTs was 1.4% and 0.05%, respectively. Over the other than EC in 463 cases (71.1%), and unknown in 109 years, a slight increase in prevalence was observed for cases (16.7%). ACTs and ECs, as well as ECs only, whereas the preva- lence of ACTs did not equally increase (Fig.  4). Nota- Characteristics of cartilaginous lesions bly, the total number of MRI scans performed per year Of the 672 lesions in total, radiological diagnosis was decreased from 2007 to 2014 and remained constant EC in 650 tumours (96.7%), and ACT in 22 lesions thereafter (Fig. 4). (3.3%). Mean tumour size of all cartilaginous lesions In 651 (1.45%) out of 44,762 patients with MRI scans was 1.6 ± 1.1  cm. Thirty lesions (4.5%) were sized 4  cm of either knee joint taken from 01.01.07 to 01.03.20, a or more, with the largest lesion measuring 9.0  cm (cra- benign cartilaginous lesion was detected incidentally. In nio-caudal). The most common location was the distal 17 of these patients, two lesions in the same knee were femur in 490 cases (72.9%), and the majority of lesions found. In additional 4 patients, a cartilaginous lesion was was located in the metaphysis (58.9%, n = 396). In relation Woltsche et al. Cancer Imaging (2023) 23:50 Page 6 of 9 Fig. 4 Yearly number of patients with at least one MRI scan (n = 44,762) and estimated prevalence of ECs and ACTs around the knee joint to the medullary canal, 386 lesions were located cen- Discussion trally (57.4%), and the remaining 286 lesions peripherally The prevalence of benign cartilage lesions – i.e. enchon - (42.6%). Periosteal reaction was present in 2 cases (0.3%), dromas and ACTs – is difficult to estimate since they and endosteal scalloping in 15 (2.2%; Table 1). seldom cause symptoms and therefore usually present All 672 lesions were analysed for radiologic features as incidental finding on imaging. In this study, based on that allow assessment of tumours dignity [4, 5, 12]. In 44,762 MRI scans of the knee performed at a single radi- comparison to ECs, those lesions classified as ACT were ology institute within 13.2 years, a prevalence of 1.45% significantly larger (p < 0.001), rather located in the proxi- for cartilage lesions around the knee was found. mal fibula (22.7% vs. 6.0%; p = 0.011), and peripherally To the authors knowledge, this is the largest MRI- to the medullary canal (p < 0.001), had been diagnosed based study on the prevalence and characteristics of via contrast-enhanced MRI (p < 0.001), and presented cartilage lesions around the knee. The herein discovered with periosteal reaction (p = 0.001), medullary oedema prevalence is lower than the one observed in some previ- (p = 0.014), and endosteal scalloping (p < 0.001; Table  1). ous analyses using MRI scans of the knee. Stomp et al. Superficial scalloping was present in one EC and 2 ACTs, reported on an estimated population prevalence of 2.8% whereas deep endosteal scalloping was found in 12 ACTs. for cartilage tumours around the knee joint, based on Notably, endosteal scalloping was present in 11.4% of 1,285 MRI scans of the right knee [3]. In the studies by tumours located in the proximal fibula, compared to 1.5% Douis et al. and Walden et al., the prevalence of enchon- and 1.6% in the proximal tibia and distal femur, respec- dromas on knee MRIs in children [10] and adults [2], tively (p = 0.007). respectively, amounted to both 2.9%. On the other hand, our figure is comparable to the 0.8% (healthy individu - als) to 1.5% (knee osteoarthritis patients) reported by Grainger et al. [9]. Yet, with 601 knee MRI scans from Woltsche et al. Cancer Imaging (2023) 23:50 Page 7 of 9 Table 1 Characteristics of benign cartilaginous tumours detected on MRI scan, split by radiological diagnosis of EC vs. ACT (n = 672) Total Count (%) EC (n = 650) ACT (n = 22) p-value* Tumour size (in cm; mean ± SD) 1.6 ± 1.1 1.5 ± 0.9 5.1 ± 1.9 < 0.001** Side Left 312 (46.4) 301 (46.3) 11 (50.0) 0.829 Right 360 (53.6) 349 (53.7) 11 (50.0) Bone Distal femur 490 (72.9) 474 (72.9) 16 (72.7) 0.011 Proximal tibia 137 (20.4) 136 (20.9) 1 (4.6) Proximal fibula 44 (6.6) 39 (6.0) 5 (22.7) Patella 1 (0.1) 1 (0.2) 0 (0.0) Location Epiphysis 80 (11.9) 80 (12.3) 0 (0.0) < 0.001 Epimetaphysis 70 (10.4) 65 (10.0) 5 (22.7) Metaphysis 396 (58.9) 391 (60.2) 5 (22.7) Metadiaphysis 32 (4.8) 27 (4.1) 5 (22.7) Diaphysis 93 (13.9) 86 (13.2) 7 (31.9) Patella 1 (0.1) 1 (0.2) 0 (0.0) Location in Relation to Medullary Canal Central 386 (57.4) 383 (58.9) 3 (13.6) < 0.001 Peripheral 286 (42.6) 267 (41.1) 19 (86.4) Periosteal Reaction No 670 (99.7) 650 (100.0) 20 (90.9) 0.001 Yes 2 (0.3) 0 (0.0) 2 (9.1) Medullary Oedema No 666 (99.1) 646 (99.4) 20 (90.9) 0.014 Yes 6 (0.9) 4 (0.6) 2 (9.1) Endosteal Scalloping No 656 (97.8) 649 (99.9) 8 (36.4) < 0.001 Yes 15 (2.2) 1*** (0.1) 14 (63.6) Contrast Agent No 591 (88.0) 582 (89.5) 9 (40.9) < 0.001 Yes 81 (12.0) 68 (10.5) 13 (59.1) * Fisher’s exact test ** t-test *** superficial scalloping Woltsche et al. Cancer Imaging (2023) 23:50 Page 8 of 9 healthy individuals and 123 from patients with knee radiological features indicative of ACT are not utterly osteoarthritis, the number of scans is nearly 60-times defined. Related to this, radiological diagnosis had not lower than in our cohort. been confirmed with histopathology. Given the sampling An even lower prevalence of 0.2% for cartilage lesions error associated with differentiation between EC and around the knee derives from an autopsy study dating ACT upon histopathological analysis [11], it is believed back to 1928 [8]. However, this figure has to be inter - that additional histopathology would not have consid- preted in its historical context, considering that – other erably altered results obtained. Another limiting fac- than anatomical dissection – MRI scans are highly sensi- tor is the retrospective design, relying on MRI scans of tive in detecting even smallest cartilage lesions, reflected the knee performed for any reason with no particular by a mean size of 1.6 cm calculated for all tumours found focus on detection of cartilaginous lesions. On the other in the present study. hand, the prevalence of cartilage lesions was estimated In our study, only 22 lesions were classified as ACTs based on an abundance of scans with a uniform protocol amounting to an overall prevalence of 0.05%. This fig - adopted by the radiology institute where images derived ure is significantly lower than the prevalence of 0.4% from. reported by Stomp et al. [3]. The discrepancy in ACT prevalence can be explained by the fact that the authors Conclusions chose a cut-off of 2  cm in lesion’s size to primarily dif - In summary, the current study revealed an overall preva- ferentiate between enchondromas and ACTs, whilst we lence of 1.45% for cartilage lesions around the knee joint. used a threshold of 5 cm as proposed by van de Sande et Of all cartilage lesions diagnosed on MRI, 3.3% exhibited al. [11]. features indicative of ACT. Whilst a constant increase in According to van Praag et al., frequency of ACT diag- prevalence was found for enchondromas over 13.2 years, nosis increased between 1989 and 2013, whereas the one prevalence remained constant for ACTs. of higher grade chondrosarcomas remained constant Abbreviations [13]. Other than in our MRI-based study, the numbers EC Enchondroma reported by van Praag et al. were based on histopatho- ACT Atypical cartilaginous tumour PD Proton density logically proven ACTs and higher-grade chondrosar- FS Fat suppression comas [13]. The authors concluded that apart from an VF Field of view ageing population, more frequent imaging and consecu-M Matrix TR Repetition time tive referral of worrisome cartilage lesions to surgery may TE Echo time have caused the increase in incidence of ACTs [13]. ST Slice thickness However, in our study, prevalence for ACTs did not IG Interslice gap IQR Interquartile ranges increase with time, whilst the one of cartilage lesions in general, and enchondromas in particular, steadily grew Acknowledgements from 1.07% to 2007 to 1.8% in 2019 (Fig.  4). Improving Not applicable. image resolution with time and thus increasing sensitivity Authors’ contribution for even smallest enchondromas can serve as an explana- JNW: data acquisition, data analysis and interpretation, manuscript tion for this. This hypothesis is also strengthened by the preparation. MAS: study design, data analysis and interpretation, statistical analysis, fact that the yearly number of knee MRIs used for final manuscript editing. estimation of cartilage lesions’ prevalence even showed a DS: quality control of data and algorithms, manuscript editing, manuscript slight decrease with time. review. MB: data analysis and interpretation, manuscript review. Our findings show that enchondroma represents a fre - AL: study concepts, study design, quality control of data and algorithms, data quent and important incidentally diagnosed benign bone analysis and interpretation, manuscript editing, manuscript review. tumour. Although prevalence of benign cartilage lesions All authors read and approved the final manuscript. around the knee joint might have been overestimated by Funding previous studies, this study confirms that enchondroma This research received no specific grant from any funding agency in the (1.4%) is an important differential diagnosis of intraosse - public, commercial, or not-for-profit sectors. ous lesions around the knee, with a 28 times higher prev- Data Availability alence in comparison to their intermediate counterpart The datasets used and/or analysed during the current study are available from ACT (0.05%). the corresponding author on reasonable request. There are some limitations that should be considered regarding the results of the current study. The herein observed prevalence of ACTs around the knee has to be interpreted with caution, given that differentiation between EC and ACT was MRI based only, and that Woltsche et al. Cancer Imaging (2023) 23:50 Page 9 of 9 5. Mulligan ME. How to diagnose Enchondroma, Bone Infarct, and Chondrosar- Declarations coma. Curr Probl Diagn Radiol. 2019;48(3):262–73. 6. Flemming DJ, Murphey MD. Enchondroma and chondrosarcoma. Semin Ethics approval and consent to participate Musculoskelet Radiol. 2000;4(1):59–71. The local medical ethics committee (“Ethikkomission Medizinische Universität 7. Douis H, Saifuddin A. The imaging of cartilaginous bone tumours. I. Benign Graz”) has approved the study (33–630 ex 20/21): “Es besteht kein Einwand lesions. Skeletal Radiol. 2012;41(10):1195–212. gegen die Durchführung der Studie in der vorliegenden Form.” 8. Scherer E, Exostosen. Enchondrome und ihre Beziehung zum Periost. Z für Pathologie. 1928;36:587–605. Consent for publication 9. Grainger R, Stuckey S, O’Sullivan R, Davis SR, Ebeling PR, Wluka AE. What is Not applicable. the clinical and ethical importance of incidental abnormalities found by knee MRI? Arthritis Res Ther. 2008;10(1):R18. Competing interests 10. Douis H, Davies AM, James SL, Kindblom LG, Grimer RJ, Johnson KJ. Can MR The authors declare that they have no competing interests. imaging challenge the commonly accepted theory of the pathogenesis of solitary enchondroma of long bone? Skeletal Radiol. 2012;41(12):1537–42. Received: 5 November 2022 / Accepted: 19 May 2023 11. van de Sande MAJ, van der Wal RJP, Navas Cañete A, van Rijswijk CSP, Kroon HM, Dijkstra PDS, et al. Radiologic differentiation of enchondromas, atypical cartilaginous tumors, and high-grade chondrosarcomas-improving tumor- specific treatment: a paradigm in transit? Cancer. 2019;125(19):3288–91. 12. Douis H, Parry M, Vaiyapuri S, Davies AM. What are the differentiating clinical and MRI-features of enchondromas from low-grade chondrosarcomas? Eur References Radiol. 2018;28(1):398–409. 1. Brien EW, Mirra JM, Kerr R. 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Enchondroma versus chondrosarcoma in the appendicular skeleton: dif- ferentiating features. Radiographics. 1998;18(5):1213–37. quiz 44 – 5. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Cancer Imaging Springer Journals

Prevalence and characteristics of benign cartilaginous tumours of the knee joint as identified on MRI scans

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Abstract

Background Enchondromas (EC) and atypical cartilaginous tumours (ACT ) of the knee joint represent benign/ intermediate chondromatous neoplasms of the bone that are most commonly discovered incidentally. Based on small to intermediate-sized cohorts, the prevalence of cartilaginous tumours of the knee as visible in MRI is estimated at 0.2–2.9%. This study aimed at verifying/challenging these numbers via retrospective examination of a larger, uniform patient cohort. Methods Between 01.01.2007 and 01.03.2020, 44,762 patients had received an MRI of the knee for any indication at a radiologic centre. Of these, 697 patients presented with MRI reports positive for cartilaginous lesions. In a three-step workflow, 46 patients were excluded by a trained co-author, a radiologist and an orthopaedic oncologist, as wrongly being diagnosed for a cartilage tumour. Results Of 44,762 patients, 651 presented with at least one EC/ACT indicating a prevalence of 1.45% for benign/ intermediate cartilaginous tumours of the knee joint (EC: 1.4%; ACTs: 0.05%). As 21 patients showed 2 chondromatous lesions, altogether 672 tumours (650 ECs [96.7%] and 22 ACTs [3.3%]) could be analysed in terms of tumour characteristics: With a mean size of 1.6 ± 1.1 cm, most lesions were located in the distal femur (72.9%), in the metaphysis of the respective bone (58.9%) and centrally in the medullary canal (57.4%). Conclusions This study revealed an overall prevalence of 1.45% for cartilage lesions around the knee joint. Whilst a constant increase in prevalence was found for ECs over 13.2 years, prevalence remained constant for ACTs. Keywords Enchondroma, Atypical cartilaginous tumour, Prevalence, Knee joint, MRI *Correspondence: Maria Anna Smolle maria.smolle@medunigraz.at Department of Orthopaedics and Trauma, Medical University of Graz, Graz, Austria Diagnostikum Graz, Graz, Austria © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Woltsche et al. Cancer Imaging (2023) 23:50 Page 2 of 9 Background Tumor” (cartilaginous tumour), “chondrogene Läsion” Enchondromas (ECs) and atypical cartilaginous tumours (chondrogenic lesion), “chondrogener Tumor” (chon- (ACTs, formerly known as chondrosarcoma grade 1) are drogenic tumour), “Chondrosarkom” (chondrosarcoma), cartilaginous neoplasms located in the medullary canal “ACT - atypischer chondromatöser Tumor“ (atypical [1–4]. While ECs represent the most common intramed- chondromatous tumour), “atypische chondromatöse ullary benign cartilaginous lesion [1, 2], ACTs constitute Läsion“ (atypical chondromatous lesion). an intermediate neoplasm that is often hard to distin- Altogether, 697 patients’ MRI reports were positive for guish from EC [2, 3]. However, distinction between these at least one search term and were subsequently analysed lesions is of great importance, as ACTs – on the contrary in further detail (Fig.  1). Of these, 21 patients had to be to ECs – require surgical treatment [3, 4]. Certain imag- excluded due to the following reasons: In 11 patients, ing features allow some assessment of the tumours’ dig- reason for referral had been a suspected cartilaginous nity: large lesion size, as well as presence of periosteal tumour but MRI could not confirm this tentative diagno - reaction, endosteal scalloping or perilesional edema can sis; 3 patients had MRI reports containing not only find - help differentiate ACT from EC [ 2, 5]. The latter are most ings of MRIs of the knee but also of other body regions, often found in the short bones of the hand (40–65%), in whom they had been diagnosed with a cartilage lesion; whilst long bones (femur, humerus, tibia) are the second 2 patients were initially suspected to have an enchon- most common location for EC, accounting for 25% of droma, yet follow-up MRIs led to a change of primary cases [6, 7]. diagnosis; 5 patients had undergone surgical removal of ECs typically present clinically silent, with large lesions the cartilaginous lesion prior to index imaging. eventually causing pain or – especially in short bones – Reports of the remaining 676 patients were re-exam- pathologic fractures [3, 5]. Therefore, this tumour is most ined together with related MRI scans, and a definitive commonly found incidentally during routine clinical radiologic diagnosis of cartilaginous tumours was con- imaging (X-ray, CT [computed tomography], MRI [mag- firmed in 635 patients. However, 41 patients had incon - netic resonance imaging]). Consequently, the true preva- clusive reports and images. Therefore, the advice of a lence of EC remains uncertain [3, 7]. Thus far, five studies senior radiologist was sought for these cases. Thereafter, have analysed the prevalence of benign cartilaginous 20 more patients were excluded, as they did not show lesions around the knee based on MRI, reaching figures typical features of EC/ACT, resulting in 656 patients ulti- between 0.2 and 2.9% [2, 3, 8–10]. mately eligible. As all five studies were based on small to intermediate- MRI-based differentiation into EC (Fig.  2) and ACT sized cohorts, this study aimed at verifying these num- (Fig.  3) was made based on tumour characteristics sus- bers via retrospective examination of a larger, uniform picious of aggressive behavior as proposed by Mulli- patient cohort with MRI scans of the knee. gan et al. [5], Murphey et al. [4], van de Sande et al. [11] and Douis et al. [12], i.e. tumour size > 4.9  cm, periosteal Methods reaction, perilesional edema or deep endosteal scallop- Study design and study population ing involving ≥ 2/3 of cortical thickness. With either one The current retrospective study was performed with data of these features being positive, chondrogenic lesions deriving from a private radiologic centre, performing – were classified as ACT. All tumours exhibiting at least apart from numerous other imaging modalities – MRI one of these features were thoroughly examined by an scans of all body sites. The local medical ethics com - experienced orthopedic oncologist, who excluded 5 mittee has approved the study (33–630 ex 20/21) that more patients due to diagnosis of bone infarction (n = 3), involved patients having received an MRI of the knee for postoperative changes (n = 1) and intraosseous ganglion any indication between 01.01.2007 and 01.03.2020. Dur- (n = 1). ing that time, 44,762 patients had undergone at least one Overall, 651 patients had a cartilaginous tumour, with knee MRI scan. Of these, 5182 had undergone MRI scans 21 patients presenting with 2 cartilaginous lesions at the of both knee joints, resulting in a total of 24,125 and same time, resulting in 672 cases of EC/ACT. 25,819 MRI scans of the left and right knee, respectively. All MRI reports of the knee were searched for at least Lesion analysis one of the following terms by one of the co-authors (J.W.) MRI was considered positive for a cartilaginous tumour who had performed an extensive study of literature and on identification of a smooth or lobulated lesion that pre - had received intensive training on imaging features of sented itself as a focal geographic area within the bone cartilage lesions before data acquisition: “Enchondrom” marrow, showing low signal intensity on proton-den- (enchondroma), “kartilaginäre Läsion” (cartilaginous sity-weighted and on T1-weighted images and high sig- lesion), “cartilaginäre Läsion” (cartilaginous lesion), “kar- nal intensity on proton-density fat-suppressed images. tilaginärer Tumor” (cartilaginous tumour), “cartilaginärer Lesions positive for these characteristics but strictly Woltsche et al. Cancer Imaging (2023) 23:50 Page 3 of 9 Fig. 1 Flow chart representing the filtering of patients with a cartilaginous tumour subchondral in location had to be excluded, as they MRI most likely represent different entities such as subchon - MRI examinations were performed on two different 3T dral cysts, intraosseous ganglia, subchondral edema or MRI systems (Siemens Magnetom Skyra/Siemens Magne- contusion. tom Vida; both Siemens Healthcare Diagnostics GmbH, Apart from patient gender and age, the following Austria) with a 15/18-channel knee coil. Sequences tumour-specific features were ascertained: lesion size acquired were (1) coronal proton density (PD) with fat (maximal tumour diameter in cm), lesion site (femur, suppression (FS) (field of view (VF) 160/140 mm; Matrix tibia, fibula, patella), tumour location (eccentric or cen - (M) 307 × 384/307 × 384; repetition time (TR) 3000/3200 tral; epiphyseal, epimetaphyseal, metaphyseal, metadi- ms; echo time (TE) 34/25 ms; slice thickness (ST) 3/3 aphyseal, diaphyseal), endosteal scalloping, perilesional mm; interslice gap (IG) 0.6/0.6  mm); (2) transversal edema and periosteal reaction. Furthermore, indication PD with FS (VF 160/150 mm; M 307 × 384/307 × 384; for MRI (tumour associated symptoms or follow-up TR 5460/4110 ms; TE 37/35 ms; ST 2.5-3/3 mm; IG examinations; no tumour related indication; no docu- 0.6/0.6 mm); (3) sagittal PD with FS (VF 160/140 mm; M mented indication) and whether the patients had under- 307 × 384/307 × 384; TR 2920/2920 ms; TE 34/34 ms; ST gone dynamic contrast MRI was ascertained. 3/3 mm; IG 0.6/0.6  mm); (4) coronal T1 weighted turbo spin echo (TSE) (VF 160/140 mm; M 346 × 384/290 × 484; Woltsche et al. Cancer Imaging (2023) 23:50 Page 4 of 9 Fig. 2 EC of the right tibia: (A) proton density, fat suppression, coronal, turbo spin echo; (B) proton density, fat suppression, transversal, turbo spin echo; (C) proton density, fat suppression, sagittal, turbo spin echo; (D) t1, coronal, turbo spin echo (year of MRI: 2016) TR 690/690 ms; TE 11/19 ms; ST 3/3 mm; IG 0.6/0.6 mm; calculated based on the diagnosis of a benign cartilagi- flip angle (FA) 180°/150°). nous lesion per patient, and not based on the number of Gd-DTPA (dose 2 ml/kg body weight) via venous cartilage lesions found in total. In line with this, patients access was administered in 77 of 651 patients (81 of without ECs/ACTs undergoing MRI scans of both knee 672 tumours), followed by an MRI examination with joints during the defined period were counted once only the sequence “(4) coronal T1 weighted turbo spin echo” for calculation of prevalence. Normally and non-nor- that was subtracted from the native T1 sequence. Addi- mally distributed variables were given as means and cor- tionally, T1 sequences with fat suppression in different responding standard deviations, as well as medians and dimensions were recorded. corresponding interquartile ranges (IQR), respectively. Fisher’s exact test and t-test were used to assess differ - Statistical analysis ences in binary (or ordinary) and continuous variables, Statistical analyses were carried out with Stata Version respectively, depending on radiological diagnosis. A 16.1 for Mac (StataCorp, College Station, Texas, US). p-value of < 0.05 was considered statistically significant. Patient demographics were summarized for based on the total number of patients with cartilaginous lesions. Tumour demographics were summarized from the total number of lesions found in patients. Prevalence was Woltsche et al. Cancer Imaging (2023) 23:50 Page 5 of 9 Fig. 3 ACT of the left femur: (A) proton density, fat suppression, coronal, turbo spin echo; (B) proton density, fat suppression, transversal, turbo spin echo; (C) proton density, fat suppression, sagittal, turbo spin echo; (D) t1, coronal, turbo spin echo (year of MRI: 2016) Results found both in the left and right knee, amounting to 672 Prevalence of benign cartilaginous lesions tumours in total. Mean age of patients with EC/ACT was Between 01.01.07 and 01.03.2020, the prevalence 52.1 ± 13.1 years, and 48.4% were males (n = 315). The rea - of benign cartilaginous lesions (i.e. ECs and ACTs) son for referral to MRI was suspected EC based on pre- amounted to 1.45%. In detail, the separate prevalence for ceding imaging in 79 cases (12.2%), a suspected pathology ECs and ACTs was 1.4% and 0.05%, respectively. Over the other than EC in 463 cases (71.1%), and unknown in 109 years, a slight increase in prevalence was observed for cases (16.7%). ACTs and ECs, as well as ECs only, whereas the preva- lence of ACTs did not equally increase (Fig.  4). Nota- Characteristics of cartilaginous lesions bly, the total number of MRI scans performed per year Of the 672 lesions in total, radiological diagnosis was decreased from 2007 to 2014 and remained constant EC in 650 tumours (96.7%), and ACT in 22 lesions thereafter (Fig. 4). (3.3%). Mean tumour size of all cartilaginous lesions In 651 (1.45%) out of 44,762 patients with MRI scans was 1.6 ± 1.1  cm. Thirty lesions (4.5%) were sized 4  cm of either knee joint taken from 01.01.07 to 01.03.20, a or more, with the largest lesion measuring 9.0  cm (cra- benign cartilaginous lesion was detected incidentally. In nio-caudal). The most common location was the distal 17 of these patients, two lesions in the same knee were femur in 490 cases (72.9%), and the majority of lesions found. In additional 4 patients, a cartilaginous lesion was was located in the metaphysis (58.9%, n = 396). In relation Woltsche et al. Cancer Imaging (2023) 23:50 Page 6 of 9 Fig. 4 Yearly number of patients with at least one MRI scan (n = 44,762) and estimated prevalence of ECs and ACTs around the knee joint to the medullary canal, 386 lesions were located cen- Discussion trally (57.4%), and the remaining 286 lesions peripherally The prevalence of benign cartilage lesions – i.e. enchon - (42.6%). Periosteal reaction was present in 2 cases (0.3%), dromas and ACTs – is difficult to estimate since they and endosteal scalloping in 15 (2.2%; Table 1). seldom cause symptoms and therefore usually present All 672 lesions were analysed for radiologic features as incidental finding on imaging. In this study, based on that allow assessment of tumours dignity [4, 5, 12]. In 44,762 MRI scans of the knee performed at a single radi- comparison to ECs, those lesions classified as ACT were ology institute within 13.2 years, a prevalence of 1.45% significantly larger (p < 0.001), rather located in the proxi- for cartilage lesions around the knee was found. mal fibula (22.7% vs. 6.0%; p = 0.011), and peripherally To the authors knowledge, this is the largest MRI- to the medullary canal (p < 0.001), had been diagnosed based study on the prevalence and characteristics of via contrast-enhanced MRI (p < 0.001), and presented cartilage lesions around the knee. The herein discovered with periosteal reaction (p = 0.001), medullary oedema prevalence is lower than the one observed in some previ- (p = 0.014), and endosteal scalloping (p < 0.001; Table  1). ous analyses using MRI scans of the knee. Stomp et al. Superficial scalloping was present in one EC and 2 ACTs, reported on an estimated population prevalence of 2.8% whereas deep endosteal scalloping was found in 12 ACTs. for cartilage tumours around the knee joint, based on Notably, endosteal scalloping was present in 11.4% of 1,285 MRI scans of the right knee [3]. In the studies by tumours located in the proximal fibula, compared to 1.5% Douis et al. and Walden et al., the prevalence of enchon- and 1.6% in the proximal tibia and distal femur, respec- dromas on knee MRIs in children [10] and adults [2], tively (p = 0.007). respectively, amounted to both 2.9%. On the other hand, our figure is comparable to the 0.8% (healthy individu - als) to 1.5% (knee osteoarthritis patients) reported by Grainger et al. [9]. Yet, with 601 knee MRI scans from Woltsche et al. Cancer Imaging (2023) 23:50 Page 7 of 9 Table 1 Characteristics of benign cartilaginous tumours detected on MRI scan, split by radiological diagnosis of EC vs. ACT (n = 672) Total Count (%) EC (n = 650) ACT (n = 22) p-value* Tumour size (in cm; mean ± SD) 1.6 ± 1.1 1.5 ± 0.9 5.1 ± 1.9 < 0.001** Side Left 312 (46.4) 301 (46.3) 11 (50.0) 0.829 Right 360 (53.6) 349 (53.7) 11 (50.0) Bone Distal femur 490 (72.9) 474 (72.9) 16 (72.7) 0.011 Proximal tibia 137 (20.4) 136 (20.9) 1 (4.6) Proximal fibula 44 (6.6) 39 (6.0) 5 (22.7) Patella 1 (0.1) 1 (0.2) 0 (0.0) Location Epiphysis 80 (11.9) 80 (12.3) 0 (0.0) < 0.001 Epimetaphysis 70 (10.4) 65 (10.0) 5 (22.7) Metaphysis 396 (58.9) 391 (60.2) 5 (22.7) Metadiaphysis 32 (4.8) 27 (4.1) 5 (22.7) Diaphysis 93 (13.9) 86 (13.2) 7 (31.9) Patella 1 (0.1) 1 (0.2) 0 (0.0) Location in Relation to Medullary Canal Central 386 (57.4) 383 (58.9) 3 (13.6) < 0.001 Peripheral 286 (42.6) 267 (41.1) 19 (86.4) Periosteal Reaction No 670 (99.7) 650 (100.0) 20 (90.9) 0.001 Yes 2 (0.3) 0 (0.0) 2 (9.1) Medullary Oedema No 666 (99.1) 646 (99.4) 20 (90.9) 0.014 Yes 6 (0.9) 4 (0.6) 2 (9.1) Endosteal Scalloping No 656 (97.8) 649 (99.9) 8 (36.4) < 0.001 Yes 15 (2.2) 1*** (0.1) 14 (63.6) Contrast Agent No 591 (88.0) 582 (89.5) 9 (40.9) < 0.001 Yes 81 (12.0) 68 (10.5) 13 (59.1) * Fisher’s exact test ** t-test *** superficial scalloping Woltsche et al. Cancer Imaging (2023) 23:50 Page 8 of 9 healthy individuals and 123 from patients with knee radiological features indicative of ACT are not utterly osteoarthritis, the number of scans is nearly 60-times defined. Related to this, radiological diagnosis had not lower than in our cohort. been confirmed with histopathology. Given the sampling An even lower prevalence of 0.2% for cartilage lesions error associated with differentiation between EC and around the knee derives from an autopsy study dating ACT upon histopathological analysis [11], it is believed back to 1928 [8]. However, this figure has to be inter - that additional histopathology would not have consid- preted in its historical context, considering that – other erably altered results obtained. Another limiting fac- than anatomical dissection – MRI scans are highly sensi- tor is the retrospective design, relying on MRI scans of tive in detecting even smallest cartilage lesions, reflected the knee performed for any reason with no particular by a mean size of 1.6 cm calculated for all tumours found focus on detection of cartilaginous lesions. On the other in the present study. hand, the prevalence of cartilage lesions was estimated In our study, only 22 lesions were classified as ACTs based on an abundance of scans with a uniform protocol amounting to an overall prevalence of 0.05%. This fig - adopted by the radiology institute where images derived ure is significantly lower than the prevalence of 0.4% from. reported by Stomp et al. [3]. The discrepancy in ACT prevalence can be explained by the fact that the authors Conclusions chose a cut-off of 2  cm in lesion’s size to primarily dif - In summary, the current study revealed an overall preva- ferentiate between enchondromas and ACTs, whilst we lence of 1.45% for cartilage lesions around the knee joint. used a threshold of 5 cm as proposed by van de Sande et Of all cartilage lesions diagnosed on MRI, 3.3% exhibited al. [11]. features indicative of ACT. Whilst a constant increase in According to van Praag et al., frequency of ACT diag- prevalence was found for enchondromas over 13.2 years, nosis increased between 1989 and 2013, whereas the one prevalence remained constant for ACTs. of higher grade chondrosarcomas remained constant Abbreviations [13]. Other than in our MRI-based study, the numbers EC Enchondroma reported by van Praag et al. were based on histopatho- ACT Atypical cartilaginous tumour PD Proton density logically proven ACTs and higher-grade chondrosar- FS Fat suppression comas [13]. The authors concluded that apart from an VF Field of view ageing population, more frequent imaging and consecu-M Matrix TR Repetition time tive referral of worrisome cartilage lesions to surgery may TE Echo time have caused the increase in incidence of ACTs [13]. ST Slice thickness However, in our study, prevalence for ACTs did not IG Interslice gap IQR Interquartile ranges increase with time, whilst the one of cartilage lesions in general, and enchondromas in particular, steadily grew Acknowledgements from 1.07% to 2007 to 1.8% in 2019 (Fig.  4). Improving Not applicable. image resolution with time and thus increasing sensitivity Authors’ contribution for even smallest enchondromas can serve as an explana- JNW: data acquisition, data analysis and interpretation, manuscript tion for this. This hypothesis is also strengthened by the preparation. MAS: study design, data analysis and interpretation, statistical analysis, fact that the yearly number of knee MRIs used for final manuscript editing. estimation of cartilage lesions’ prevalence even showed a DS: quality control of data and algorithms, manuscript editing, manuscript slight decrease with time. review. MB: data analysis and interpretation, manuscript review. Our findings show that enchondroma represents a fre - AL: study concepts, study design, quality control of data and algorithms, data quent and important incidentally diagnosed benign bone analysis and interpretation, manuscript editing, manuscript review. tumour. Although prevalence of benign cartilage lesions All authors read and approved the final manuscript. around the knee joint might have been overestimated by Funding previous studies, this study confirms that enchondroma This research received no specific grant from any funding agency in the (1.4%) is an important differential diagnosis of intraosse - public, commercial, or not-for-profit sectors. ous lesions around the knee, with a 28 times higher prev- Data Availability alence in comparison to their intermediate counterpart The datasets used and/or analysed during the current study are available from ACT (0.05%). the corresponding author on reasonable request. There are some limitations that should be considered regarding the results of the current study. The herein observed prevalence of ACTs around the knee has to be interpreted with caution, given that differentiation between EC and ACT was MRI based only, and that Woltsche et al. Cancer Imaging (2023) 23:50 Page 9 of 9 5. Mulligan ME. How to diagnose Enchondroma, Bone Infarct, and Chondrosar- Declarations coma. Curr Probl Diagn Radiol. 2019;48(3):262–73. 6. Flemming DJ, Murphey MD. Enchondroma and chondrosarcoma. Semin Ethics approval and consent to participate Musculoskelet Radiol. 2000;4(1):59–71. The local medical ethics committee (“Ethikkomission Medizinische Universität 7. Douis H, Saifuddin A. The imaging of cartilaginous bone tumours. I. Benign Graz”) has approved the study (33–630 ex 20/21): “Es besteht kein Einwand lesions. Skeletal Radiol. 2012;41(10):1195–212. gegen die Durchführung der Studie in der vorliegenden Form.” 8. Scherer E, Exostosen. Enchondrome und ihre Beziehung zum Periost. Z für Pathologie. 1928;36:587–605. Consent for publication 9. Grainger R, Stuckey S, O’Sullivan R, Davis SR, Ebeling PR, Wluka AE. What is Not applicable. the clinical and ethical importance of incidental abnormalities found by knee MRI? Arthritis Res Ther. 2008;10(1):R18. Competing interests 10. Douis H, Davies AM, James SL, Kindblom LG, Grimer RJ, Johnson KJ. Can MR The authors declare that they have no competing interests. imaging challenge the commonly accepted theory of the pathogenesis of solitary enchondroma of long bone? Skeletal Radiol. 2012;41(12):1537–42. Received: 5 November 2022 / Accepted: 19 May 2023 11. van de Sande MAJ, van der Wal RJP, Navas Cañete A, van Rijswijk CSP, Kroon HM, Dijkstra PDS, et al. Radiologic differentiation of enchondromas, atypical cartilaginous tumors, and high-grade chondrosarcomas-improving tumor- specific treatment: a paradigm in transit? Cancer. 2019;125(19):3288–91. 12. Douis H, Parry M, Vaiyapuri S, Davies AM. What are the differentiating clinical and MRI-features of enchondromas from low-grade chondrosarcomas? Eur References Radiol. 2018;28(1):398–409. 1. Brien EW, Mirra JM, Kerr R. Benign and malignant cartilage tumors of bone 13. van Praag Veroniek VM, Rueten-Budde AJ, Ho V, Dijkstra PDS, Fiocco M, van de and joint: their anatomic and theoretical basis with an emphasis on radiol- Sande MAJ. Incidence, outcomes and prognostic factors during 25 years of ogy, pathology and clinical biology. I. The intramedullary cartilage tumors. treatment of chondrosarcomas. Surg Oncol. 2018;27(3):402–8. Skeletal Radiol. 1997;26(6):325–53. 2. Walden MJ, Murphey MD, Vidal JA. Incidental enchondromas of the knee. AJR Am J Roentgenol. 2008;190(6):1611–5. Publisher’s Note 3. Stomp W, Reijnierse M, Kloppenburg M, de Mutsert R, Bovée JV, den Heijer M, Springer Nature remains neutral with regard to jurisdictional claims in et al. Prevalence of cartilaginous tumours as an incidental finding on MRI of published maps and institutional affiliations. the knee. Eur Radiol. 2015;25(12):3480–7. 4. Murphey MD, Flemming DJ, Boyea SR, Bojescul JA, Sweet DE, Temple HT. Enchondroma versus chondrosarcoma in the appendicular skeleton: dif- ferentiating features. Radiographics. 1998;18(5):1213–37. quiz 44 – 5.

Journal

Cancer Imaging – Springer Journals

Published: May 25, 2023

Keywords: Enchondroma; Atypical cartilaginous tumour; Prevalence; Knee joint; MRI

References

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