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 ossifica- tion(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 develo- pment 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 fre- quent 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 syn- drome,