SUMMARY Chondroblastoma and chondromyxoid fibroma are benign but locally aggressive bone tumors of cartilage origin. Chondroblastoma, which is generally round and lytic in character, is a painful tumor located in the long bone epiphysis and apophysis. Chondromyxoid fibroma, on the other hand, is a radiolucent and loculated tumor located in the long bone metaphysis. They are rare in both tumors and are especially important in terms of high recurrence rates after treatment. As with other locally aggressive bone tumors, curettage, which is often used with local adjuvants, followed by bone grafting or synthetic bone filling materials is the treatment. The most common complication is tumor recurrence. Although very rarely, chondroblastoma can metastasize. Key Words: Chondroblastoma; chondromyxoid fibroma; cartilage tumors; bone tumors ABS TRACT Chondroblastoma and chondromyxoid fibroma are benign but locally aggressive cartilage producing bone tumors. Chondroblastoma, a round shaped and lytic lesion, is a painful tumor located in the epiphysis of long bones. Chondromyxoid fibroma is a radiolucent and loculated tumor in the metaphysis of long bones. Management of these rare tumors is challenging. They may have similar histopathologic features. The treatment is generally curettage with local adjuvants and bone grafting of cement application. The most common complications are recurrence of the tumors. Chondroblastoma can rarely metastasize.
Chondroblastoma is a rare, locally aggressive and rarely metastasized benign bone tumor that is usually found in the epiphysis or apophysis of long bones. It was first described in the literature as a cartilage-containing giant cell tumor (DHT) by Kolodny in 1927. 1 Then, in 1931, Codman described the lesion as an “epiphyseal chondromatous DHT” affecting the proximal humerus, hence the lesion was also referred to as a “Codman tumor”. 2 Finally, in 1942, Jaffe and Lichtenstein defined this tumor as benign chondroblastoma of the bone as an entity different from DHT, which can be found not only in the proximal humerus but also in all bone tissue.3 EPIDEMIOLOGY Chondroblastoma accounts for 1-2% of all primary bone tumors and benign bone tumors. It constitutes approximately 5% of benign bone tumors.4 The male/female ratio is approximately 2/1.5,6 The majority of patients are under the age of 20, but there are cases reported in the literature between the ages of 2 and 73.5 Chondroblastoma is most often found in the distal femur, proximal tibia Although it is located in the proximal femur and proximal humerus, it can be seen in flat bones such as the scapula, patella, sternum, and pelvis.4,5,7 This tumor is seen in small or flat bones at a later age than in long bones.8,9 About 0.5% of chondroblastomas One of them is located in the spine and often involves the posterior elements. ETIOLOGY As with many primary bone tumors, the etiology of chondroblastoma is unknown. Considering the age and localization of the tumor, its relationship with the proteins regulating the development of the epiphysis was investigated and it was shown that it is associated with a process for chondrogenesis in which the cartilage signaling molecules, parathyroid hormone-related protein and fibroblast growth factor play an active role. CLINICAL Chondroblastoma Enneking benign bone tumor classification are usually classified as stage-2 (active) or 3 (aggressive). Because of its localization, it can be clinically confused with epiphyseal tumors and painful processes of joint origin (such as inflammatory arthritis). Similarly, since some patients attribute this pain to trauma or sports-related injuries, there may be a significant delay in diagnosis, with an average of 1 year between the onset of complaints and diagnosis.13,15 Local swelling, increase in synovial fluid in the joint adjacent to the lesion, muscle atrophy and In lower extremity cases, disruption may accompany the clinical picture.4,6,7 In patients with delayed admission, the mass may enlarge and become palpable.16 Although pathological fractures of long bones are rarely seen, subchondral fractures may occur in lesions located in the foot.9 RADIOLOGY Classical radiographic examination of chondroblastoma Its appearance is a well-circumscribed oval or round lesion of lytic character, adjacent to an open physeal line, located within the epiphysis.15 A sharp-lined sclerotic border is often seen around this lesion. The lesion may contain mottled or cloudy areas of calcification. The size of the lesion varies on radiographs, but is usually less than 4 cm. 3,4,14,17 Calcifications are seen especially in patients with incomplete skeletal maturity. Periosteal bone formation is rare on radiographs, but edema is usually observed adjacent to the periosteum on MRI.18 Rarely, especially In patients seen at older ages or delayed at presentation, chondroblastoma may exhibit an aggressive clinic and radiology.4,16,19 As in histopathology, chondroblastomas with secondary PCC usually differ from normal chondroblastomas on radiography and make diagnosis difficult. Periarticular cystic changes are frequently seen in lesions located in bones such as the patella.9,20 Most chondroblastomas occur in the epiphysis of long bones.15 Although a small lesion may extend along the entire epiphyseal line, it is usually confined to the epiphysis or part of the apophysis.21 True metaphyseal chondroblastoma is rare; Most of the reported cases are metaphyseal extensions of the epiphyseal lesion. 21 Diaphyseal chondroblastoma has been reported as a few case reports in the literature. 22 Chondroblastomas located in small bones may progress more aggressively with loss of cortical continuity and bone destruction. 9 CT clearly shows punctate calcifications in the cartilage matrix seen in some cases (Figure 1B). On magnetic resonance imaging (MRI), chondroblastoma is usually hypointense on T1-weighted images and is characterized by varying degrees of hypointense and hyperintense signals on T2-weighted images (Figure 1C). On MRI, bone marrow and soft tissue edema can be seen in the periphery of the lesion following lobulation and administration of contrast material. Mononuclear cell proliferation is seen in pita bread with clinical examination and conventional radiographs. The tumor is characterized by round, oval or polygonal chondroblasts with well-circumscribed cytoplasm. Cells may have one or two round-oval nuclei or no nuclei.14 Some cells may have large nuclei without showing nuclear atypia.24 Again, few mitotic figures can be observed. There are multinucleated osteoclast type giant cells scattered among the chondroblasts. There may be foci of the chondroid matrix formed by chondroblasts.24 Dystrophic calcification can sometimes be seen with the cells surrounded, and this is called a “chicken wire” view, which is helpful in diagnosis but is not necessary for a definitive diagnosis.3,6,14,24 Secondary aneurysmal bone cyst (ACC) may accompany the picture in 15-32% of chondroblastoma cases.5,14,17 Although the reason for this association is not clear, there are hypotheses such as mechanical stress, trauma, and bleeding.9 Histopathological findings include less aggressive chondroblastomas with aggressive behavior. Although they do not differ in terms of metastasis and local recurrence.24 Immunohistochemically, chondroblastoma shows great positivity against collagen type II and S-100 protein. DIFFERENTIAL DIAGNOSIS of the bone in the differential diagnosis of chondroblastoma, simple bone cyst, ABC, enchondroma, eosinophilic granuloma , fibrous dysplasia, clear cell chondrosarcoma, subacute osteomyelitis (Brodie abscess). In the presence of subchondral cyst, Legg-Calvé-Perthes disease or osteochondritis dissecans should also be included in the differential diagnosis. In addition, especially in developing countries, tuberculosis should be considered in the differential diagnosis as chondroblastoma may mimic periarticular pain and bone lesion. Chondromyxoid fibroma is a very rare benign bone tumor that is a mixture of cartilage, fibrous and myxoid tissue, usually found in the long bones of the lower extremities. It was first described in the literature by Jaffe and Lichtenstein in 1948.38 Prior to this definition, this lesion was thought to be enchondroma, chondrosarcoma, or myxoma of bone. 15 EPIDEMIOLOGY Chondromyxoid fibroma accounts for <0.5% of all primary bone tumors and approximately 1% of benign bone tumors. 39 The male-female ratio is approximately 2/1.39 Patients are most often diagnosed in the third decade of life. 40,41 Most of these tumors are located in the metaphysis of the long bones in the lower extremities, close to the apophysis or intracortically.41 Rarely, the lesion epiphysis or the diaphysis.22,42 The most common site is the proximal tibia.41,43 Cases localized to the ilium, ribs, distal femur, metatarsals, and distal tibia other than the proximal tibia have been reported.41 Unlike chondroblastoma, it is rarely seen in the humerus.41 ETIOLOGY Chondromyxoid fibroma, has myofibroblastic differentiation via the growth factor b-1 (TGF-β1) signaling pathway.44 Small cells in mature chondrocytes The Sox9 gene, which is responsible for the expression of rind-specific genes (particularly collagen type II synthesis) and chondrocytic differentiation, is found in chondroblastoma and chondromyxoid fibroma.45,46 The Sox9 gene is particularly active in the early stages of chondrocytic differentiation. The fact that chondroblastoma is a more immature tumor than chondromyxoid fibroma is explained by the higher Sox9 gene positivity in chondromyxoid fibroma than chondroblastoma.45 CLINIC Chondromyxoid fibroma is mostly classified as stage-2 (active) or 3 (aggressive) according to the Enneking benign bone tumor classification .12 The time between first symptom and diagnosis is usually less than 1 year. Its symptoms are similar to chondroblastoma, except that it presents with less pain. The duration of symptoms ranges from a few months to several years. The second most common symptom is palpable swelling. The lesion may be painful on palpation and the mass may gradually enlarge. Local swelling is more common, especially in small bones. Disruption, decreased range of motion of the adjacent joint, and pathological fractures can be seen, albeit rarely.38,43,47,48 RADIOLOGY Chondromyxoid fibroma is classically seen as a metaphyseal medullary lesion with sclerotic margins, lytic and radiolucent in character. Most lesions are sharply circumscribed and the cortex is partially or completely affected.39,41 They are usually located close to the cortex in the metaphysis of long bones and are less than 5 cm in diameter. The tumor rarely extends beyond the growth plate to the epiphysis or diaphysis.15 In small bones, chondromyxoid fibroma usually covers the entire width of the bone, causing cortical thinning and expansion. Sclerosis seen at tumor margins resembles the trabecular structure of bone in radiology. However, macroscopic and microscopic examination showed that this tumor did not have a bony septum, and this structure was named pseudotrabeculation (Figure 2A). It is seen in 34 of them.39,49 Calcification is more common in flat bones, especially over the age of 40.49 CT shows cortical integrity and calcification of the matrix well. Due to varying amounts of myxoid and cartilage tissue on MRI, the central tumor is hyperintense on T2-weighted spin-echo images and STIR sequences. It is caused by highly vascularized connective tissue at the tumor border. HISTOPATHOLOGY In macroscopy; chondromyxoid fibroma appears as a firm tumor mass that is lobulated and sharply demarcated from the bone marrow, yellow, grayish-white, or blue-gray.15 In microscopy; It contains three different components with myxomatous, fibrous and chondroid areas. Lobules formed by satellite or spindle-shaped cells in the intercellular space with abundant myxoid or chondroid components constitute the classical histological findings. In approximately 50% of cases, giant cells are found adjacent to the lobules.39,41 While the center of the lobules is hypocellular, the periphery is hypercellular. The interlobular space consists of oval or spindle-shaped cells. Rarely observed mitotic activity is often seen in the interlobular area. Although atypical mitotic features cannot be found, some cells have large nuclei of irregular size and shape.41 Wu et al. reported cellular atypia in 18% of cases, and added that there was no change in the nucleus/cytoplasm ratio. 41 Lesions on the hands and feet are more likely to have atypical cells. (liquefaction) does not show. However, approximately 30% of chondromyxoid fibroma cases have small foci of liquefaction exchange.15 Cyst formation, necrosis, foam cells, secondary aneurysmal cyst foci, and areas of hyaline cartilage are unusual findings. 41 Calcifications are present in approximately one-third of lesions and present as thin plaque deposits. .41 Immunohistochemical analysis of chondromyxoid fibroma shows great positivity against collagen type II and S-100 protein. COMPLICATIONS The most common complication known after chondromyxoid fibroma treatment is the recurrence of the lesion, which can reach up to 20-30% of the lesion.39 Histologically large and irregular nucleus in chondromyxoid fibroma. lesions with a higher probability of recurrence. Tumors diagnosed at an early age have been reported to have a higher recurrence rate.50 Sarcomatous change can be observed in chondromyxoid fibromas, although there are very few reports in the literature.41 No metastasis from chondromyxoid fibroma has been reported in the literature.