Osteochondroma: Radiological Diagnosis, Complications and Variants

Home , Exostosis, Osteochondroma, Osteochondromatosis

Revista Chilena de Radiología. Vol. 19 Nº 2, año 2013; 73-81. MUSCULOESQUELÉTICO Osteochondroma: radiological diagnosis, complications and variants

Doctors Marco Cañete P, Elena Fontoira M, Begoña Gutiérrez San José, Slavina Mancheva M.

Servicio de Radiología Músculo-esquelética. Fundación Jiménez Díaz. Madrid, España.

Abstract: Understanding and recognising the spectrum of appearances of osteochondroma is important because it represents the most frequent pseudotumoral bone lesion. There are pathognomonic radiological features that are evident with the currently available imaging methods. The recognition of these features and their potential complications and variants, enables a correct diagnosis to be made, the identification of possible complications and is a guide for the therapeutic decisions of non-conclusive cases. Keywords: Bone tumors, Dysplasia, Exostosis, Osteochondroma.

Resumen: Conocer el espectro de apariencias del osteocondroma es importante, ya que representa le- sión pseudotumoral más frecuente del hueso y posee unas características radiológicas patognomónicas evidenciables con los distintos métodos de imagen disponibles actualmente. El reconocimiento de estas características radiológicas, de sus posibles complicaciones y variantes permite establecer el diagnóstico correcto, identificar las posibles complicaciones y guiar el manejo terapéutico de los casos no concluyentes. Palabras clave: Displasia, Exostosis, Neurológicas, Osteocondroma, Tumores óseos.

Cañete M, et al. Osteocondroma: diagnóstico radiológico, complicaciones y variantes. Rev Chil 2013; 19(2): 73-81. Correspondencia: Marco A. Cañete Prette / MACañ[email protected] Paper received 28 november 2012, accepted for publication 2 june 2013.

Introduction Pathophysiology and epidemiology Osteochondroma represents the most common Osteochondromas are considered developmen- pseudotumoral bone lesion. The radiological tal lesions rather than true neoplasms(1). The lesion, pathognomonic characteristic of this tumor is the cortical according to the World Health Organization (WHO), and marrow continuity of the lesions with the adjacent is defined as an osteochondral exostosis with cortical bone(1). The lesions may be solitary or multiple, the and marrow continuity, respectively(10). It is believed that latter forming part of the hereditary multiple exostoses these lesions result from the separation of a fragment syndrome(2). These lesions may also appear with of the epiphyseal growth cartilage, which herniates complications such as bone deformities, fractures(1,3), through normal bone that surrounds the growth plate(1). neurological or vascular compromise(1,4,5), bursa In the case of multiple osteochondromas its asso- formation and more rarely, malignant transformation(6,7). ciation has been described with mutations of the EXT The most common variants include subungual exostosis, 1 and EXT 2 genes, which intervene in the heparan dysplasia epiphysealis hemimelica (Trevor’s disease) sulfate proteoglycans biosynthesis, involved in the (1,8), parosteal osteochondromatous proliferation (Nora’s epiphyseal growth plate, and with radiation, which could lesion)(9) and Florid reactive periostitis. In general, produce dedifferentiation of the cartilaginous tissue the diagnosis can be made with an X-ray, according growth, among others(1). In general, osteochondromas to the characteristics of the tumor, although other appear mostly in children or adolescents, without methods such as ultrasound imaging, especially CT gender predilection, although some authors consider and MRI may be useful in uncertain cases, or with it more frequent in males(10,11). the appearance of symptomatic lesions or in unusual places(1). The aim of this paper is to illustrate the Solitary osteochondroma various presentations of osteochondroma, as well The vast majority of osteochondromas are as its complications and variants. solitary lesions(1). The most common sites are

73 Dr. Marco Cañete M, et al. Revista Chilena de Radiología. Vol. 19 Nº 2, año 2013; 73-81. the long bones of the lower limb, mostly the distal Figure 2a. X-ray of end of the femur and proximal tibia(12) (Figure 1) side of wrist: Pisiform and in the upper limb, the humerus(1). Sites of Osteochondroma: rare occurrence described in literature include the benign aspect exophytic lobulated bones of the hands and feet, the scapula, pelvis, (1,13-15) bone lesion spine (Figures 2a,b and 3a,b), ribs and sites dependent on the (16,17) rarer still such as the temporomandibular joint pisiform bone (arrow). or soft tissues such as the Hoffa fat pad around the knee(18) (Figure 4a, b), although it should be noted that an osteochondroma can arise in any bone that develops from endochondral ossification(1). The majority are asymptomatic lesions(18) and discovered incidentally, and if they appear with symptoms, the most common of them is the development of a slow-growing mass(1).

Figure 2b. Axial CT of the wrist with bone reconstruction: Pisiform Osteochondroma: benign aspect exophytic and lobulated cortical bone lesion dependent on the pisiform bone (arrow).

Figure 1. X-ray AP of knee: an exophytic cortical bone Figure 3a. Axial CT of the thorax with bone reconstruction: lesion in the metaphyseal-diaphyseal junction of the Scapular Osteochondroma: benign aspect cortical bone medial distal femur can be observed, with cortical marrow lesion dependent on the medial border of the left scapula continuity (arrow). (arrow). 74 Revista Chilena de Radiología. Vol. 19 Nº 2, año 2013; 73-81. MUSCULOESQUELÉTICO

Figure 3b. 3D pedunculated (Figures 5 and 6), radiography often CT scapula being sufficient for diagnosis (1). The most frequent reconstruction. location in long bones is usually the metaphysis Scapular and tendon insertion sites(10). However, in flat bones Osteochondroma: diagnosis may be more difficult. Hyaline cartilage sessile exophytic bone lesion layer can be visualized in radiographs as areas of dependent on semicolon calcification, but in cases with absence medial border of of mineralization other imaging methods may be the scapula. required. Ultrasound allows visualization of the cartilage layer, which is seen as a hypoechoic area on the bone cortex being studied, but proves more useful for the study of complications such as aneurysms, thrombosis or bursitis(10). Regarding CT, this allows excellent visualization of the cortico- medullary continuity of the lesion, and may be even more useful in areas of complex anatomy, such as the bones of the spine, shoulder or pelvis(10). However, Figure 4a. Lateral some authors believe that this imaging method knee X-ray: Femoral may not be suitable for measuring the thickness Osteochondroma: of the cartilage layer, an important criterion for cortical exophytic differentiation with chondrosarcoma(1). Finally, MRI bone lesion allows better visualization than radiography in the dependent on cortico-medullary continuity of lesions in complex metaphysic- areas(1). Cortical continuity is displayed as a thin diaphysis junction hypointense line on all pulse sequences, and the bone of distal femur marrow maintains a yellow marrow signal (Figure (arrow). 7 a,b). In addition, MRI is considered as the best method for visualizing the structures surrounding the lesion, its effect on these (vascular and nerve compromise), data complication (pseudoaneurysms, edema) and unmineralized cartilage layer, which displays a high signal on T1 and on T2, due to its water content, allowing the adequate measurement F i g u r e 4 b . of thickness for these features(1) (Figure 8). It must Right knee MRI, be noted that the presence of edema is a sign of saggital T1 sequence: Sessile complication and may indicate the presence of a (10) Osteochondroma chondrosarcoma . of the distal femur: exophytic lesion in distal femoral diaphysis with cortical medullary continuity (arrow)

The radiological features are quite typical, displaying an exophytic lesion with cortical and medullary continuity protruding from the adjacent Figure 5. Axial MRI of thigh, Axial T1 sequence: Sessile (19) bone . Regarding its implantation base, this can Osteochondroma of the distal femur: exophytic bone lesion be wide or narrow, representing the two types dependent on femoral diaphysis (arrow) with cortical and of solitary osteochondroma, the sessile and medullary continuity. 75 Dr. Marco Cañete M, et al. Revista Chilena de Radiología. Vol. 19 Nº 2, año 2013; 73-81.

Figure 8. Axial MRI of hip, T2 STIR sequence: Sessile Femur Osteochondroma: bone lesion dependent on left femur, Figure 6. Axial MRI of hip, T2 SPIR sequence: Pedunculated visualizing layer of hyperintense hyaline cartilage (arrow). Osteochondroma: bone tumoration (arrow) irregularly pedunculated (asterisk), dependent on posterior edge of the right femoral neck, with cortical medullary continuity.

Multiple hereditary exostosis (MHE) This is a syndrome characterized by the development of multiple osteochondromas and shows an autosomal dominant genetic pattern(1). Some authors consider diagnosis, the radiological presence of at least two osteochondromas in yuxta-epiphyseal regions of long bones. It is considered that the appearance of solitary osteochondromas is six times more frequent than in this syndrome. The clinical aspect and complications are the same as for solitary lesions, although patients with this condition can experience a variety of orthopedic deformities, the most common amongst these being the shortening of the forearm(2,21). The presence of complications is greater in this syndrome, as there are a greater number of lesions(1). It is believed that the genetic basis of this syndrome Figure 7a. Axial MRI of thigh, T1 sequence: Sessile Femur is related to mutations of the EXT1 and 2 genes(2). Osteochondroma: exophytic cortical bone lesion (arrow) dependent on distal femoral diaphysis with cortical medullary The most feared complication is the malignization continuity. of the osteochondromas to chondrosarcomas, as we will see further on, but it is worth saying that it is thought that this transformation is more frequent in osteochondromas of patients with this syndrome(10). In differential diagnosis, Trevor’s disease must be considered, in that this as well as osteochondroma are diagnosed at an early age and its development is related to the closure of the growth plate. However, lesions in Trevor’s disease affect the lower limbs uni- laterally and are limited to the medial or lateral side of these (hemimelica). Finally, malignization of lesions has not been reported in the latter(2).

Complications of osteochondroma Among the most frequent complications can be found the presence of bony deformities, fractures, vascular and neurological compromise, bursa formation and malignization(22,23). Figure 7b. Axial MRI of thigh, T2 sequence: Sessile Bone deformity: it is considered the most common Femur Osteochondroma: exophytic cortical bone lesion presentation and is usually more frequent in MHE (arrow) dependent on distal femoral diaphysis with cortical patients. The disease mostly affects the knees, hips medullary continuity. and ankle, in order of frequency(1).

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Due to mass effect, in some cases, adjacent bone erosion can be observed and in the case of visceral contact, these may also be affected as, for example, the case of osteochondromas of the ribs which can produce pleural effusion and / or hemothorax(1,24). Fracture: This is another complication to consider and, consequently, causes pain, which can be a form of presentation(10), being more frequent at the base of pedunculated lesions(1). Considering the mass effect which these lesions can produce, being exophytic, it is not uncommon that complications such as vascular or nerve compression syndrome arise, and in fact, these can appear in various forms (Figure 9c).

Figure 9c. Lateral X-ray of knee: Fibular Osteochondroma: exophytic cortical bone lesion dependent on posterior metaphyseal-diaphyseal junction of the fibula, with cortical medullary continuity (arrow).

Vascular syndromes: Vessel displacement (Figure 10), stenosis, vascular occlusion and pseudoaneurysms may occur, the latter being more frequent at knee level, usually involving the popliteal artery(1,25) or occurring as an arterial thrombosis(26). Finally, in the case of rib lesions, the presentation has been described as thoracic outlet syndrome due to occlusion of the adjacent vessels(27).

9a. Sagittal MRI of knee, SPIR DP sequence: Fibular Osteochondroma: exophytic bone lesion dependent on the fibula (hollow arrow), mass effect with displacement of posterior femoral neurovascular bundle (arrow).

9b. Sagittal MRI of knee, T1 sequence: Fibular Figure 10. Angio CT of lower limbs, 3D reconstruction: Osteochondroma: mass effect can be observed at the level tibiofibular bone lesion (arrow) producing evident ipsilateral of the posterior muscle compartment of the calf. tibiofibular trunk displacement.

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Nerve involvement: Central and/or peripheral Malignization: Malignant transformation is the most Osteochondromas can produce nerve compression feared complication and it is due to a chondrosarco- syndromes, generating entrapment symptoms, the ma arising in the cartilage cap of the lesion(1,7). The most common being the peroneal nerve caused by lesions most susceptible to malignant transformation a tibial lesion(1). More rarely described has been the are of the pelvis, hips and shoulders. Findings suggest sciatic nerve compression by femoral neck lesions(4). malignization consists in the growth of a previously In this aspect MRI is an excellent imaging method, as stable lesion, irregular borders, interior radiolucent it is able to demonstrate the nerve signal change and areas, erosions or destruction of adjacent bone and muscle atrophy with fat replacement of the involved soft tissue mass with irregular calcifications. The muscles (Figure 11)(1,10). Finally, one interesting fact is most important image criterion to consider is the that central lesions that produce nerve compression thickness of cartilage cap, there being differences in patients with hereditary multiple exostoses, are among authors as to the pathological and normal usually solitary(1). value of this(1,32). Because of their high water content, on MRI it shows high signal intensity on T2 and low on T1. Usually found adjacent to an area of low signal representing the perichondrium(10).

Figure 11. Axial MRI of hip, T2 STIR sequence, enlarged image: Osteochondroma of left femur with hyperintense cartilaginous cap and unchanged signal displacement of the adjacent sciatic nerve (arrow).

Figure 12a. Dorsal tumor ultrasound: Oval heterogeneous Bursa formation: In general, this develops at sites image with well-defined borders and subscapularis intramusclar where there is friction between structures, namely location, corresponding to an infected bursa (arrow). between the exostosis and an adjacent structure(1). This usually occurs around the scapula(11,28,29), in the hip and shoulder. This complication is seen as a soft tissue mass near an osteochondroma, which may contain mineralized chondroid areas that can simulate malignization. Ultrasound is very useful to distinguish the anechoic bursal collection from the solid hypoechoic tissue of a hyaline cartilage cap. The bursa, in turn, can become complicated, can cause infection, inflammation, or bleeding(1); the presence of a mass due to a reactive infected bursa may clinically suggest the malignization of a lesion(30). In this respect, MRI is an excellent imaging method that allows diagnosis by demonstrating the peripheral contrast enhancement or the presence Figure 12b. Axial MRI of the chest wall, T1 SPIR sequence of septa in the cases of super-infection (Figure 12 with gadolinium: Bursa between left scapular osteochondroma a-c)(30). Another aspect to consider is the presence (not displayed) and chest wall: rounded image with localized of a chondrometaplasia resulting in a secondary peripheral enhancement at the level of left posterior chest osteochondromatosis from the bursa synovial(1,31). wall, suggesting superinfection.

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exophyitic growth from a cortical bone surface and is composed of cartilage, bone and fibrous tissue, mainly affecting the proximal and middle phalanges and the metacarpals and metatarsals(43) (Figure 15 a, b). The radiographs reveal, in a more advanced stage, bony excrescences, with a separation base between the lesion and bone, due to the existen- ce of cartilage tissue interposed between them, although continuity with the lesion can be seen in some cases(1). The CT as well as demonstrating Figure 12c. Axial MRI of chest wall, T2 SPIR sequence: these findings, also allows evaluation of the pre- Bursa between left scapular osteochondroma (not sence or absence of continuity with the adjacent displayed) and chest wall: irregular hyperintense cortex and the presence of soft-tissue involvement. image corresponding to bursa (arrow) with internal The final diagnosis is provided by the pathological hypointense septa, suggesting super-infection. anatomy, as these lesions may be confused with paraosteal osteosarcoma and/or conventional osteochondroma. The first, rarely affects bones Variants: Dysplasia epiphysealis hemimelica so small, and the second, in addition to the histo- (Trevor’s disease). This consists of an osteocartila- pathological analysis, has other features such as ginous growth on the medial or lateral side of one cortical and medullary continuity. Lastly, this lesion or more epiphysis(1,33,34). It largely affects the long can be confused with a malignant process, due to (1,43) bones of the lower limb and tarsal bones, especially its high recurrence rate . the knee, ankle and talus(8,35). There are rare cases reported of the hip, patella, spine(36-38) and hand(39). Conclusion We describe three forms, a localized, a classical, Osteochondroma represents the most common affecting more than one area in a single limb, and bone tumor, and it presents some typical radiological a generalized form, the bilateral affectation consi- features, mainly cortical and medullary continuity. In dered rare(1,40). The first usually affects the ankle; doubtful cases and to study variants and/or compli- the second affects epiphysis, most often around cations, other imaging with CT or MRI in particular the knee and ankle; and the last, the entire lower may be necessary, to be able to arrive at a diagnosis extremity(1,34) (Figures 13 and 14 a-c). The radiolo- in most cases. Knowledge of the spectrum of findings gical findings in pediatric patients show affected in this lesion allows the radiologist to make a correct ossification centers prematurely eccentric, lobulated diagnosis and assists in directing the management and increased in size. In addition, calcifications can of the patient toward a correct treatment. be seen. Subsequently, typical epiphyseal exostosis with cortical and medullary continuity can be seen. The CT and MRI, allow viewing of these aspects, as well as cartilage component detail. You can also see areas with low signal on T1 and T2, which represent areas of calcification or ossification(1,41). In differential diagnosis the osteochondromas must de considered, although Trevor lesions occur in pediatric patients and adolescents, and arises in the epiphysis. The osteochondroma, however, occurs between ages 10 and 30 years and originates in the metaphysis of long bones(42). Other Variants: Other rarer variants include Turret exostosis, which consists of an extracortical mass dependent on the proximal or middle phalanges of the hand. Similar lesions have been described at the level of tendon and ligament insertions, known as traction exostosis. Similar lesions have been described in feet and hands, the florid reactive periostitis and paraosteal osteochondromatous Figure 13. CT of left ankle, 3D reconstruction, external (1) proliferation or Nora’s lesion . The latter affects anterior view: Trevor’s disease: bone lesion dependent on patients between the third and fourth decades of distal tibiotalar joint (arrow), which produces remodeling of life, with no gender predilection(9). It consists of an the tibioperoneal mortise.

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Figure 15a. X-ray AP of left hand: Nora’s lesiony: benign aspect cortical bone tumor, dependent on diaphysis radial slope of proximal phalanx of 4th Finger.

Figure 14a. X-ray of side of the knee: Trevor’s disease: exophytic bone lesion dependent on anterior tibial tuberosity (arrow), with “horn” appearance, corresponding to epiphyseal osteochondroma.

Figure 15c. Axial CT of hand, 2nd and 3rd fingers: Nora’s lesion: cortical bone tumor dependent on phalanx of 4th Finger and of benign aspect.

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