345 PROFESSIONAL ARTICLE Diagnostics and treatment of enchondromas Copyright (c) 2022 Slovenian Medical Journal. This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Diagnostics and treatment of enchondromas Diagnostična obravnava in zdravljenje enhondromov Rok Vojković,1 David Martinčič,1,2 Blaž Mavčič1,2 Abstract Enchondromas are benign intramedullary tumours of mature hyaline cartilage, accounting for 10–25% among all benign bone tumours.They are present in almost 3% of magnetic resonance examinations of knees and shoulders as an asymp- tomatic random finding. This paper presents epidemiology, clinical picture, imaging diagnostics, differential diagnostics, biopsy indications, histopathology, clinical monitoring, and treatment of enchondromas. Randomly discovered asymp- tomatic intramedullary solitary enchondromas in long bones mainly do not require treatment, as the risk of subsequent malignant alteration is less than 1%. Enchondromas in small bones of hands and feet are treated by excochleation biopsy due to a high risk of pathological fracture. Cartilaginous tumours exhibiting growth, local pain, or aggressive radiological characteristics require treatment at a tertiary facility with a possible biopsy and decision on observation/discharge/resec- tion. The most complex clinical challenge is distinguishing common enchondromas from rare atypical cartilage tumors and even rarer chondrosarcomas, whereby the BACTIP guidelines can be very useful. Izvleček Enhondromi so benigni intramedularni tumorji iz zrelega hialinega hrustanca, ki obsegajo 10–25 % vseh benignih kostnih tumorjev. Kot naključna najdba brez simptomov so prisotni pri 2–3 % magnetnoresonančnih preiskavah kolen in ramen. Članek predstavi enhondrome z vidika epidemiologije, klinične slike, slikovne diagnostike, diferencialne diagnostike, in- dikacij za biopsijo, histopatologije, kliničnega spremljanja in zdravljenja. Naključno odkritih intramedularnih solitarnih enhondromov dolgih kosti brez izraženih simptomov v večini primerov ni treba zdraviti, tveganje za kasnejšo maligno alteracijo pa je manjše od 1 %. Enhondrome v malih kosteh rok in nog se zdravi z ekskohleacijsko biopsijo zaradi možnosti patološkega zloma. Hrustančne spremembe, ki rastejo, povzročajo bolečine ali imajo po slikovnih preiskavah t.i. agresivne značilnosti, zahtevajo obravnavo v terciarni ustanovi in odločitev glede indikacij za biopsijo, opazovanje, izpraznitev ali izrez. Najtežji klinični izziv je razločevanje pogostih enhondromov od redkih atipičnih hrustančnih tumorjev in še redkejših hondrosarkomov, pri čemer pa so nam v oporo smernice BACTIP. 1 Department of Orthopaedic Surgery, University Medical Centre Ljubljana, Ljubljana, Slovenia 2 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia Correspondence / Korespondenca: Blaž Mavčič, e: blaz.mavcic@kclj.si Key words: enchondroma; biopsy; incidental finding; BACTIP guidelines Ključne besede: enhondrom; biopsija; naključna najdba; smernice BACTIP Received / Prispelo: 7. 2. 2021 | Accepted / Sprejeto: 29. 5. 2021 Cite as / Citirajte kot: Vojković R, Martinčič D, Mavčič B. Diagnostics and treatment of enchondromas. Zdrav Vestn. 2022;91(7–8):345–52. DOI: https://doi.org/10.6016/ZdravVestn.3226 eng slo element en article-lang 10.6016/ZdravVestn.3226 doi 7.2.2021 date-received 29.5.2021 date-accepted Surgery, orthopaedics, traumatology Kirurgija, ortopedija, travmatologija discipline Professional article Strokovni članek article-type Diagnostics and treatment of enchondromas Diagnostična obravnava in zdravljenje enhondro-mov article-title Diagnostics and treatment of enchondromas Diagnostična obravnava in zdravljenje enhondro-mov alt-title enchondroma, biopsy, incidental finding, BACTIP guidelines enhondrom, biopsija, naključna najdba, smernice BACTIP kwd-group The authors declare that there are no conflicts of interest present. Avtorji so izjavili, da ne obstajajo nobeni konkurenčni interesi. conflict year volume first month last month first page last page 2022 91 7 8 345 352 name surname aff email Blaž Mavčič 1,2 blaz.mavcic@kclj.si name surname aff Rok Vojković 1 David Martinčič 1,2 eng slo aff-id Department of Orthopaedic Surgery, University Medical Centre Ljubljana, Ljubljana, Slovenia Ortopedska klinika, Univerzitetni klinični center Ljubljana, Ljubljana, Slovenija 1 Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia Medicinska fakulteta, Univerza v Ljubljani, Ljubljana, Slovenija 2 Slovenian Medical Journallovenian Medical Journal 346 SURGERY, ORTHOPAEDICS, TRAUMATOLOGY Zdrav Vestn | July – August 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3226 1 Introduction Enchondromas are benign tumours of the mature hy- aline cartilage, most commonly located in the long and short tubular bones. The term enchondroma denotes cartilage tumours that grow within the bone; outside the bone, they are known as chondromas (1). The vast majority of enchondromas are asymptomatic and do not require treatment; however, with imaging studies, they can be difficult to differentiate from other locally aggres- sive or malignant cartilage tumours (2). Cartilage tu- mours are classified into three groups according to their aggressiveness: enchondroma, atypical cartilaginous tumour (previously known as grade I chondrosarcoma) and high-grade chondrosarcoma (grade II, III and de- differentiated chondrosarcoma) (2). Although the inci- dence of benign and malignant mesenchymal tumours has remained unchanged for decades (3), the number of incidentally detected cartilage lesions has increased dramatically in Slovenia and worldwide due to the wider availability of magnetic resonance imaging (MRI). For this reason, in recent years, there has been a tendency to establish guidelines for the uniform treatment of en- chondromas (4-6). The purpose of this article is to pres- ent enchondromas: their epidemiology, clinical presen- tation, imaging studies, differential diagnostics, biopsy indications, histopathology, clinical monitoring and treatment. The main focus is on distinguishing between common benign lesions and rare aggressive or malig- nant tumours. The conclusion of the article presents clinical guidelines for the treatment of enchondromas (4-5), adopted by the Orthopaedic Society of the Slove- nian Medical Association for Slovenian orthopaedic sur- geons at its annual assembly on 29 November 2019 (7). 2 Epidemiology and clinical presentation Enchondromas account for 10–25% of all benign bone tumours detected, and are the second most com- mon, behind osteochondromas. The incidence of inci- dentally detected proximal upper arm enchondromas on MRI of the shoulder is 2.1% (8), and 2.8% on MRI of the knee (9). When converted to the Slovenian population, this would mean that approximately 42,000 Slovenians have a cartilage tumour of the proximal humerus and 56,000 of the femur or tibia. The vast majority of these enchondromas are asymptomatic and will never be de- tected. Exceptions to this rule are enchondromas of the hands and feet, which can cause pathological fractures and, in most cases, can be easily diagnosed by X-ray or MRI (10). The aetiology of enchondromas is unknown. They most commonly occur between the second and sixth de- cade with a peak in the fourth and fifth decade; they are slightly more common in women (1). The majority are located in small tubular bones of the hands; among the long tubular bones, they are found in the proximal hu- merus, proximal and distal femur and tibia. Enchondro- mas in the spine and flat bones (ribs, scapula, sternum and skull roof) are very rare; in the bony pelvis, almost all cartilage tumours are malignant (11). Enchondromas occur as part of Ollier disease (multiple enchondroma- tosis) or Maffucci syndrome (in addition to multiple enchondromas, spindle-cell haemangiomas and lymph- angiomas are also present); in these cases, they are asso- ciated with an increased risk of malignant transforma- tion (12). Local pain at the enchondroma site (pain at rest, nocturnal pain) requires appropriate imaging studies, as pain may be a sign of an active or even malignant tu- mour affecting the periosteum with expansive growth. The appearance of pain in a known enchondroma may reflect its malignant transformation, but not necessarily; benign enchondromas can also be painful, while in mid- dle-aged patients, it is often difficult to distinguish be- tween tumour pain and degenerative symptoms of near- by joints (e.g. shoulder compression syndrome or initial knee osteoarthritis). On clinical examination, pain is elicited by local pressure on the bone. In addition to lo- cal examination, a comprehensive physical examination is particularly important for patients with suspected en- chondromatosis or Maffucci syndrome (2). 3 Imaging studies On plain radiographs, enchondromas of hands and feet have thin, sharply defined margins and lobulated structure, frequently with endosteal scalloping and bone expansion, sometimes even with a pathologic fracture (Figure 1). Unlike at other sites, enchondromas on the hands and feet do not normally have calcifications. Indi- vidual rare bone lesions with sharp sclerotic margins in the short tubular bones of the hands and feet are man- aged as enchondromas, unless additional investigations reveal aggressive characteristics. In differential diagno- sis, they can be enchondromas, but other benign lesions 347 PROFESSIONAL ARTICLE Diagnostics and treatment of enchondromas Figure 1: Radiographic image of a hand with multiple enchondromas of metacarpals and phalanxes. White arrows indicate unoperated enchondromas, grey arrow indicates enchondroma after curettage and filling with bone substitute – calcium triphosphate granules. cannot be excluded. In the long tubular bones (humerus, femur, tibia), enchondromas are commonly located in the medullary cavity or they are in an eccentric position with an osteolytic structure with calcifications; they do not exhibit aggressive characteristics (bone destruction and outward growth, periosteal reaction and a soft tis- sue growth) (13). Computed tomography (CT) allows better assessment of endosteal cortical surfaces in intra- medullary cartilage tumours of long tubular bones. On MRI, the tumour margins are well-circumscribed with low signal intensity on T1 sequences with high signal in- tensity on T2 sequences. The lobulated tumour margins are characteristic, and low signal intensity is observed in calcified areas (1). The Enneking staging system for benign bone tu- mours consists of three categories according to the tu- mour’s level of activity: latent tumours (G1), active, growing tumours (G2) and aggressive, rapidly growing tumours with extension through the cortex (G3) (14). The majority of asymptomatic enchondromas are latent (G1) and are incidental findings in adolescence or adult- hood. These tumours are characterized by slow, self-lim- iting growth without cortical bone weakening; they nor- mally do not grow again after puberty (Figure 2). The faster growth of grade 2 benign tumours can result in more frequent pain, but the cortex remains intact, al- though bone expansion can occur. Due to the rapid dy- namics of growth, pain is normally present in the short medical history in grade 3 tumours. There is endosteal scalloping and discontinuation of the cortex; the clinical examination may reveal a palpable soft tissue mass (Fig- ure 3). Distinguishing enchondromas from atypical car- tilaginous tumours and chondrosarcomas based on ra- diological examinations is very difficult and not always reliable (2). Therefore, observation of cartilage tumour dimensions on serial radiographs or MRI images is one of the key methods for detecting active or malignant car- tilage tumours (4-5). MRI does not clearly distinguish benign enchondro- mas from atypical cartilaginous tumours; sometimes, it may even be difficult to distinguish them from high- grade chondrosarcomas. Enchondromas show benign or intermediate malignant changes in T1 sequences with a relatively homogeneous decrease in signal, while flu- id-sensitive sequences and fluid-sensitive sequences with fat suppression show an increase in tumour signal due to the higher water content in the chondrogenic tumour matrix. In contrast-enhanced sequences, enchondromas normally have a characteristic lobulated structure with homogenous contrast uptake centrally and peripheral- ly; contrast uptake is normally even more pronounced peripherally. Due to more extensive tumour cell dedif- ferentiation, malignant chondrosarcomas no longer ex- hibit an ordered lobulated structure and have more ar- eas of necrosis, increased connective tissue and reduced tumour matrix. Thus, the lesion has an inhomogeneous appearance, particularly in sequences with high signal intensity of contrast enhancement (15). Aggressive or malignant CT or radiographic characteristics are end- osteal scalloping and bone expansion, cortical thinning or thickening and cortical infiltration (1). Peripheral bone marrow oedema around the tumour, subperiosteal oedema or soft tissue mass on MRI suggest low-grade chondrosarcoma. Features suspicious of a malignant tu- mour are also significantly greater tumour size on MRI 348 SURGERY, ORTHOPAEDICS, TRAUMATOLOGY Zdrav Vestn | July – August 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3226 Figure 2: Radiographic (A) and MRI (B) images of an incidental enchondroma of right shoulder. The lesion is located in the metaphyseal medullary cavity, is not in contact with the cortex and does not cause endosteal scalloping; it has a typical lobulated structure without oedema or other aggressive radiological features. than on radiograph, epiphyseal location or tumour ex- tension along the epiphysis; benign cartilage tumours are located in the metaphyses (13). Bone scintigraphy has lost its significance for multiple enchondromas de- tection due to whole-body MRI. Additionally, scintigra- phy cannot distinguish between benign enchondromas, atypical cartilaginous tumours and chondrosarcomas, so it is no longer suitable as a routine diagnostic method in enchondroma management. On the other hand, bone scintigraphy and positron emission tomography (PET) frequently show enchondromas as incidental findings; even though they are benign, they can significantly ac- cumulate radionuclides (2). 4 Differential diagnosis and indications for biopsy According to the World Health Organization (WHO) classification of bone tumours (16), when a benign-look- ing cartilage tumour is detected, other chondrogenic tu- mours in addition to enchondroma are considered in the differential diagnosis, depending on their tissue of origin and tumour matrix: periosteal chondroma, osteochon- droma (cartilaginous exostosis), chondromyxoid fibro- ma, atypical cartilaginous tumour (previously known as grade I chondrosarcoma), chondroblastoma and high- grade chondrosarcoma. Chondromyxoid fibroma and atypical cartilaginous tumours are considered locally aggressive, and chondroblastoma and atypical cartilag- inous tumours can rarely metastasize (<2%). A biopsy of the suspected enchondroma should be performed if malignancy cannot be ruled out, or if the clinical presentation and imaging studies suggest a lo- cally aggressive benign cartilage tumour. An inconclu- sive radiological report or physician’s doubts should not be the only reason for an unnecessary biopsy; in uncer- tain cases, a referral to a specialized tertiary institution for bone tumours must be made (in Slovenia, this is the Division of Tumour Surgery at the Department of Orthopaedic Surgery at the University Medical Center Ljubljana). As a rule, the biopsy should be performed at the ter- tiary institution that would perform definitive surgery in case the tumour proves aggressive or malignant. During a biopsy, avoidance of anatomical structures (blood vessels, nerves, certain muscle groups) and a choice of proper approach in an area where there is a possibility of a subsequent surgical tumour resection are crucial. The anatomical approach should take into account the possi- bility that, for oncological reasons, the entire biopsy ca- nal would need to be resected with a safety margin and histological examination performed during definitive surgery. Both the biopsy approach and the possible exit point of the drainage tube should be carefully chosen so 349 PROFESSIONAL ARTICLE Diagnostics and treatment of enchondromas Figure 3: Radiographic (A) and MRI (B) images of a painful atypical cartilaginous tumour in the proximal tibia; on the right lower side of the radiographic image, there is also an asymptomatic enchondroma of the proximal tibia. The atypical cartilaginous tumour exhibits aggressive features: bone expansion, endosteal scalloping, focal cortical destruction and spread into soft tissues. It is not clearly demarcated from the cancellous bone. as not to contaminate the surrounding uncontaminated compartments (2). Proper surgical technique requires care to minimize contamination tumour seeding of the biopsy canal (preferably wide-bore needle biopsy of the soft tissue tumour component or core biopsy with a drill for intramedullary lesions) and precise imaging guiding (radiographic, CT or ultrasound-guided) to ensure that a sufficiently large sample is taken from the tumour area with the most aggressive features. Each biopsy is asso- ciated with a risk of sampling error or unrepresentative samples being taken (17), as benign, well-differentiated and malignant (undifferentiated) segments can be found in a cartilage tumour. Curettage with subsequent histo- logical examination, in which the entire tumour cavity is removed, is used for small cartilage tumours of the hands and feet. In certain cases, even histological examination can- not reliably distinguish between enchondroma, atypical cartilaginous tumour and chondrosarcoma. Therefore, a comparison between the histopathological presentation and MRI, where we look for signs of cortical perme- ation, is crucial (17). In uncertain cases, they should be overseen by a multidisciplinary medical council, taking into consideration all available clinical, radiological and histopathological data (for the Republic of Slovenia, it is the Radiological-Pathological-Orthopaedic Council at the Department of Orthopaedic Surgery at the Univer- sity Medical Center Ljubljana); if necessary, histological samples should be sent to a reference centre abroad for consultation (17,18). 5 Histopathology Surgical treatment of enchondromas in most cases involves intralesional curettage, so tumours are removed in small fragments, which often makes it impossible to microscopically assess the relationship of the tumour to the surrounding bone and thus some important param- eters for separating enchondromas from other cartilage tumours (infiltrative growth, cortical erosion). A typical enchondroma has the appearance of grey-blue hyaline cartilage. Microscopic features of enchondromas are: paucicellular appearance; absence of cytological atyp- ia (chondrocyte nuclei are small, round, dark, without nucleoli); lobular growth; frequent calcifications and absence of infiltrative growth between trabeculae (1). The microscopic characteristics of enchondromas differ according to their anatomical location, so the tumour site, together with radiological findings and clinical features, must be taken into account when interpreting the microscopic image; in enchondromas of hands and feet and multiple enchondromatosis enchondromas, the 350 SURGERY, ORTHOPAEDICS, TRAUMATOLOGY Zdrav Vestn | July – August 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3226 histopathological presentation is frequently the same as in atypical cartilaginous tumours (1,19). Atypical cartilaginous tumours are microscopically slightly more densely cellular than enchondromas, cal- cifications are less extensive or absent and mild cellular atypia (larger clear nuclei with nucleoli) are present. The most important and reliable histopathological criteria for distinguishing between atypical cartilaginous tu- mours and enchondromas are the presence of a myxoid tumour matrix, infiltrative growth and endosteal scal- loping (usura). The latter two features are rarely seen in biopsy specimens of cartilaginous tumours. It should be noted that there is a morphological spectrum from the classical microscopic presentation of the enchondroma without atypical features to differently expressed atypical changes that speak in favour of an atypical cartilaginous tumour. Therefore, a correlation between histopatholog- ical picture and MRI picture is crucial for distinguishing between enchondroma and atypical cartilage tumour. In addition to the changes seen in atypical cartilagi- nous tumours, the microscopic characteristics of chon- drosarcomas (grades II and III) are increased cell densi- ty, significant cellular atypia and the presence of mitoses. These characteristics are normally so severe that in large bones, chondrosarcomas can be easily distinguished from enchondromas and atypical cartilaginous tumours (20). In the small bones of hands and feet, enchondro- mas can be densely cellular (similar to atypical cartilag- inous tumours or even grade II chondrosarcomas); im- aging studies show significant endosteal scalloping and bulging into surrounding soft tissues, so it can be very difficult to distinguish between enchondroma and chon- drosarcoma in small bones. Microscopically, the diagno- sis of chondrosarcoma of small bones can be confirmed if infiltration into soft tissues is found; finding mitoses in tumour cells also strongly suggests chondrosarcoma. Enchondromas of the bony pelvis, spine, ribs and sternum are very rare, so all cartilage tumours at these locations need to be managed as aggressive and poten- tially malignant (1,20). 6 Clinical monitoring and treatment Incidental asymptomatic intramedullary solitary enchondromas of long bones do not normally require treatment if they do not grow and cause endosteal scal- loping. The principles of treatment of cartilage tumours needs to be explained to patients in detail, as many of them express a desire for biopsy or complete remov- al of the tumour just for fear of subsequent malignant transformation. Unfortunately, patients are occasionally unnecessarily unnerved by an ambiguous radiological report in which, despite the absence of any aggressive imaging features, an unlikely differential diagnostic op- tion is mentioned: low-grade chondrosarcoma (2). As it is not always possible to reliably determine the tumour’s nature radiologically, there may be a need for additional investigations or multidisciplinary management, which is stressful for patients. In this regard, it is important to note that the possibility of transformation from solitary enchondroma to malignant disease is less than 1% (21). In case an enchondroma presents with local pain, appropriate treatment consists of thorough curettage af- ter a biopsy and bone grafting or filling the bone defect with cement. Enchondromas of small bones of the hands and feet are normally actively treated with curettage due to the possibility of pathologic fracture (1). All patients with multiple enchondromas (Ollier disease, Maffucci syndrome) should receive life-long monitoring due to increased risk of malignant transformation, which is es- timated at 15–30% (12). One of Britain’s leading sarcoma centres, The Royal Orthopaedic Hospital in Birmingham, recently devel- oped the Birmingham Atypical Cartilage Tumour Imag- ing Protocol (BACTIP) to monitor solitary cartilage tu- mours of the proximal humerus and knee (4), which, in a retrospective evaluation of 387 cases over a 10-year da- ta collection period, proved to be excellent (5). The use of BACTIP clinical guidelines for Slovenian orthopaedic surgeons was adopted by the Orthopaedic Society of the Slovenian Medical Association at its annual assembly on 29 November 2019 (7). The BACTIP protocol is based on radiological assessment of cartilage tumour length and endosteal scalloping, as shown schematically in Figure 4. Tumour length corresponds to the maximum measured tumour size on MRI, and a threshold of four centimetres determines whether the tumour is classified into Category I (tumours < 4 cm) or Category II (tu- mours ≥ 4 cm). Endosteal scalloping can be absent (A), focal (B) or generalised (C). Based on these two param- eters, tumours are classified into the first six categories (IA, IB, IC, IIA, IIB, IIC). Category III includes tumours with aggressive radiological features (bone expansion or cortical thickening, cortical destruction, periosteal reac- tion or spread into soft tissues), regardless of size. Category IA intramedullary tumours do not re- quire follow-ups, while category IB tumours with focal endosteal scalloping are recommended for a follow-up MRI after three years. If the control MRI doesn’t show changes, monitoring is concluded; if the tumour length increases by > 1 cm, the extent of endosteal scalloping increases or aggressive characteristics develop, a referral 351 PROFESSIONAL ARTICLE Diagnostics and treatment of enchondromas Figure 4: Schematic representation of the BACTIP for the monitoring of solitary cartilage tumours of the proximal humerus and knee with magnetic resonance imaging (MRI) with contrast. Summarized and adapted from (4,5). Cartilage tumour of the proximal humerus or knee ≥ 4 cm (II) IIA: without endosteal scalloping, MRI in three years IIB: focal endosteal scalloping, MRI in one year, followed by another MRI in three years IIC: generalised endosteal scalloping, referral to subspecialist for biopsy Any size with aggressive features (III) (bone expansion, cortical thickening or destruction, periosteal reaction, so tissue mass) Tumour change on control MRI? - increase in size ≥ 1 cm or - increased endosteal scalloping or - appearance of aggressive features (bone expansion, cortical thickening or destruction, periosteal reaction, so tissue mass) < 4 cm (I) IA: without endosteal scalloping, no follow-ups required IB: focal endosteal scalloping, MRI in three years IC: generalised endosteal scalloping, MRI in one year NO Discharge from follow-up YES Subspecialist referral for biopsy to a subspecialist for bone tumours is recommended. Generalised endosteal scalloping (IC) also warrants im- mediate subspecialist referral. Category II tumours without endosteal scalloping (IIA) are recommended to undergo a control MRI af- ter three years; if there is no change, the patient is dis- charged from follow-up. For tumours with focal end- osteal scalloping (IIB), a control MRI after one year is recommended, followed by another MRI after three years; if radiological changes are found, a specialist re- ferral is recommended. Cartilage tumours with a size of ≥ 4 cm (IIC) or aggressive features (III) and generalised endosteal scalloping warrant an immediate subspecialist referral for assessment of biopsy indications. 7 Conclusion Enchondroma is a common, mostly asymptomatic benign neoplasm of the mature hyaline cartilage, which does not require treatment. However, they are some- times difficult to distinguish from other benign aggres- sive or malignant cartilage tumours. The combination of the relative frequency of enchondromas in the general population and the current routine use of MRI in di- agnosing common orthopaedic diseases (e.g. meniscus and rotator cuff injuries) results in a large number of in- cidentally found enchondromas of the knee and shoul- der, requiring further clinical management. The UK-de- veloped BACTIP guidelines (4-5), also adopted for use 352 SURGERY, ORTHOPAEDICS, TRAUMATOLOGY Zdrav Vestn | July – August 2022 | Volume 91 | https://doi.org/10.6016/ZdravVestn.3226 References 1. Santini-Araujo E, Kalil RK, Bertoni F, Park YK, eds. Tumors and Tumor- Like Lesions of Bone: For Surgical Pathologists, Orthopedic Surgeons and Radiologists. London: Springer; 2015. pp. 243-51. DOI: 10.1007/978- 1-4471-6578-1 2. Nottrott M, Hardes J, Gosheger G, Andreou D, Henrichs M, Streitbuerger A. Benigne Knorpeltumoren. Was mache ich mit dem Zufallsbefund? Unfallchirurg. 2014;117(10):905-14. DOI: 10.1007/s00113-014-2578-3 PMID: 25274388 3. Novak M, ur. 2. šola o sarkomih, Onkološki inštitut, Ljubljana. 13.9.2018; Ljubljana. Ljubljana: Sekcija za onkološko kirurgijo pri SZD; 2018. 4. Patel A, Davies AM, Botchu R, James S. A pragmatic approach to the imaging and follow-up of solitary central cartilage tumours of the proximal humerus and knee. Clin Radiol. 2019;74(7):517-26. DOI: 10.1016/j.crad.2019.01.025 PMID: 30827492 5. Davies AM, Patel A, James SL, Botchu R. A retrospective validation of an imaging protocol for the management of solitary central cartilage tumours of the proximal humerus and around the knee. Clin Radiol. 2019;74(12):962-71. DOI: 10.1016/j.crad.2019.08.017 PMID: 31587800 6. Jurik AG, Hansen BH, Weber K. Solitary enchondromas-diagnosis and surveillance : danish guidelines. Radiologe. 2020;60(S1):26-32. DOI: 10.1007/s00117-020-00681-7 PMID: 32322923 7. Mavčič B. Smernice za obravnavo kostnih tumorjev v ortopedski ambulanti. Ljubljana: Slovensko zdravniško društvo. Združenje ortopedov; 2019 [cited 2021 Feb 11]. Available from: http://zdruzenje. ortopedov.si/wp-content/uploads/2019/12/Mavcic-B-2-Kostni-tumorji- smernice-29nov2019.pdf. 8. Hong ED, Carrino JA, Weber KL, Fayad LM. Prevalence of shoulder enchondromas on routine MR imaging. Clin Imaging. 2011;35(5):378-84. DOI: 10.1016/j.clinimag.2010.10.012 PMID: 21872128 9. Walden MJ, Murphey MD, Vidal JA. Incidental enchondromas of the knee. AJR Am J Roentgenol. 2008;190(6):1611-5. DOI: 10.2214/AJR.07.2796 PMID: 18492914 10. Haase SC. Treatment of pathologic fractures. Hand Clin. 2013;29(4):579- 84. DOI: 10.1016/j.hcl.2013.08.010 PMID: 24209955 11. Bloem JL, Reidsma II. Bone and soft tissue tumors of hip and pelvis. Eur J Radiol. 2012;81(12):3793-801. DOI: 10.1016/j.ejrad.2011.03.101 PMID: 21524868 12. Verdegaal SH, Bovée JV, Pansuriya TC, Grimer RJ, Ozger H, Jutte PC, et al. Incidence, predictive factors, and prognosis of chondrosarcoma in patients with Ollier disease and Maffucci syndrome: an international multicenter study of 161 patients. Oncologist. 2011;16(12):1771-9. DOI: 10.1634/theoncologist.2011-0200 PMID: 22147000 13. Gaillard F, Weerakkody Y, Jones J, Alsalam HM, Stanislavsky A, Bashir U, et al. Enchondroma. Radiopaedia.org. S.l.: S.n.; 2020 [cited 2020 Dec 12]. Available from: https://radiopaedia.org/articles/enchondroma. 14. Enneking WF, Spanier SS, Goodman MA. A system for the surgical staging of musculoskeletal sarcoma. Clin Orthop Relat Res. 1980;153:106-20. DOI: 10.1097/00003086-198011000-00013 PMID: 7449206 15. Geirnaerdt MJ, Hogendoorn PC, Taminiau AH, Bloem JL. Malignant cartilage tumors. Radiologe. 1998;38(6):502-8. DOI: 10.1007/ s001170050385 PMID: 9700771 16. Bovée JV, Flanagan AM, Lazar AJ, Nielsen GP, Yoshida A. Bone tumours. In: ; World Health OrganizationWHO Classification of Tumours. Vol. 1. Digestive System Tumours. Geneva: WHO; 2020. 17. Jennings R, Riley N, Rose B, Rossi R, Skinner JA, Cannon SR, et al. An evaluation of the diagnostic accuracy of the grade of preoperative biopsy compared to surgical excision in chondrosarcoma of the long bones. Int J Surg Oncol. 2010;2010:270195. DOI: 10.1155/2010/270195 PMID: 22312488 18. Bernard SA, Murphey MD, Flemming DJ, Kransdorf MJ. Improved differentiation of benign osteochondromas from secondary chondrosarcomas with standardized measurement of cartilage cap at CT and MR imaging. Radiology. 2010;255(3):857-65. DOI: 10.1148/ radiol.10082120 PMID: 20392983 19. Wittig J. Enchondroma. Morristown: Morristown Medical Center; 2014 [cited 2020 Dec 12]. Available from: http://www.tumorsurgery.org/ tumor-education/bone-tumors/types-of-bone-tumors/enchondroma. aspx. 20. Mavrogenis AF, Gambarotti M, Angelini A, Palmerini E, Staals EL, Ruggieri P, et al. Chondrosarcomas revisited. Orthopedics. 2012;35(3):e379-90. DOI: 10.3928/01477447-20120222-30 PMID: 22385450 21. Biondi NL, Varacallo M. Enchondroma. StatPearls. Treasure Island (FL): StatPearls Publishing; 2020. in Slovenia by the Orthopaedic Society of the Slovenian Medical Association (7), represents the basis for clinical treatment of patients with incidentally detected cartilage tumours in Slovenia. This protocol allows a safe distinc- tion between common benign enchondromas and rare cartilage tumours requiring surgical treatment based on assessment of cartilage tumour size, endosteal scalloping and the presence or absence of other aggressive radio- logical features (bone expansion or cortical thickening, cortical destruction, periosteal reaction or spread to soft tissues). Conflict of interest None declared.