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Imaging of Osteochondroma: Variants and Complications with Radiologic-Pathologic Correlation¹

¹ From the Departments of Radiologic Pathology (M.D.M., J.J.C.) and Orthopedic Pathology (F.H.G.), Armed Forces Institute of Pathology, 6825 16th St NW, Bldg 54, Rm M-133A, Washington, DC 20306; the Departments of Radiology and Nuclear Medicine, Uniformed Services University of Health Sciences, Bethesda, Md (M.D.M.); the Department of Radiology, University of Maryland School of Medicine, Baltimore (M.D.M.); the Department of Radiology, National Naval Medical Center, Bethesda, Md (D.J.F.); and the Department of Radiology, Mayo Clinic, Jacksonville, Fla (M.J.K.). Received April 12, 2000; revision requested April 27 and received May 19; accepted May 19. Address correspondence to M.D.M. (e-mail: murphey@afip.osd.mil).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Osteochondroma represents the most common bone tumor and is a developmental lesion rather than a true neoplasm. It constitutes 20%–50% of all benign bone tumors and 10%–15% of all bone tumors. Its radiologic features are often pathognomonic and identically reflect its pathologic appearance. Osteochondromas are composed of cortical and medullary bone with an overlying hyaline cartilage cap and must demonstrate continuity with the underlying parent bone cortex and medullary canal. Osteochondromas may be solitary or multiple, the latter being associated with the autosomal dominant syndrome, hereditary multiple exostoses (HME). Complications associated with osteochondromas are more frequent with HME and include deformity (cosmetic and osseous), fracture, vascular compromise, neurologic sequelae, overlying bursa formation, and malignant transformation. Malignant transformation is seen in 1% of solitary osteochondromas and in 3%–5% of patients with HME. Continued lesion growth and a hyaline cartilage cap greater than 1.5 cm in thickness, after skeletal maturity, suggest malignant transformation. Variants of osteochondroma include subungual exostosis, dysplasia epiphysealis hemimelica, turret and traction exostoses, bizarre parosteal osteochondromatous proliferation, and florid reactive periostitis. Recognition of the radiologic spectrum of appearances of osteochondroma and its variants usually allows prospective diagnosis and differentiation of the numerous potential complications, thus helping guide therapy and improving patient management.

Index Terms: Osteochondroma, 40.3113, 40.1542 • Osteochondromatosis, 40.365, 40.782 • Bone neoplasms, 40.3113, 40.1542

	LEARNING OBJECTIVES FOR TEST 5

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
After reading this article and taking the test, the reader will be able to:

• Describe the radiologic spectrum of osteochondroma, its variants, and complications, as well as features that allow distinction of malignant transformation.
  
• Understand the pathologic basis of the radiologic features of osteochondroma, its variants, and complications.
  
• Recognize the clinical and radiologic manifestations of hereditary multiple exostoses.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Osteochondroma is the most common benign tumor or tumorlike lesion of bone. The radiographic appearance of this tumor is often diagnostic and reflects its pathologic characteristics, that is, a lesion composed of cortical and medullary bone with an overlying hyaline cartilage cap. However, it is the continuity of this lesion with the underlying native bone cortex and medullary canal that is pathognomonic of osteochondroma. These lesions may be solitary or multiple, with the latter associated with the syndrome hereditary multiple exostoses (HME). Complications are commonly associated with these exophytic masses and include cosmetic and osseous deformity, fracture, vascular compromise, neurologic sequelae, overlying bursa formation, and malignant transformation. Variants of osteochondroma include subungual exostosis, dysplasia epiphysealis hemimelica, turret exostosis, traction exostosis, bizarre parosteal osteochondromatous proliferation, and florid reactive periostitis. Although radiography is often diagnostic, additional imaging modalities including bone scintigraphy, ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging are frequently employed in evaluation of these lesions, particularly when they are symptomatic or in unusual locations. The purpose of this pictorial review is to illustrate the many varied imaging appearances of both uncomplicated and symptomatic osteochondromas and their variants, with an emphasis on the pathologic cause of these manifestations.

	Pathologic Characteristics

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Osteochondromas are developmental lesions rather than true neoplasms and are often referred to as an osteocartilaginous exostosis (or simply exostosis). These lesions result from the separation of a fragment of epiphyseal growth plate cartilage, which subsequently herniates through the periosteal bone cuff that normally surrounds the growth plate (encoche of Ranvier) (1–4) (Fig 1). The mechanism for this separation is not entirely clear, although it likely results from the "cut-back" remodeling during growth of the long bone. Persistent growth of this cartilaginous fragment and its subsequent enchondral ossification (maturation) result in a subperiosteal osseous excrescence with a cartilage cap that projects from the bone surface. The stalk of the osseous protuberance must be in direct continuity with the underlying cortex and medullary canal to be considered a true osteochondroma (1–4) (Fig 2). Osteochondromas enlarge from growth at the cartilage cap, identical to a normal physeal plate. After adolescence and skeletal maturity, osteochondromas usually exhibit no further growth.

View larger version (72K): [in this window] [in a new window] [Download PPT slide]   Figure 1.   Osteochondroma development. Diagram illustrates the normal long bone with the epiphysis (tan), epiphyseal plate (blue), and "cut back" zone of remodeling (yellow). Periosteal bone cuff or encoche of Ranvier (large arrowhead) is shown with herniation of a small amount of physeal tissue (small arrowhead). This tissue migrates into the metaphysis from patient growth (arrows). The intracortical location of this physeal tissue and subsequent growth results in osteochondroma formation.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 2.   Photograph of a coronally sectioned specimen of an osteochondroma of the rib shows marrow (*) and cortical (arrowheads) continuity with the underlying parent bone. The lobulated hyaline cartilage cap (open arrow) is seen and is similar in appearance to the costal cartilage (solid arrow).

Irradiation is also associated with development of osteochondroma, related to its damaging effect on the epiphyseal plate, which causes undifferentiated cartilage tissue to migrate into the metaphysis as described by Langenskiöld and Edgren (9) and others (10–15). Subsequent growth of intracortical cartilage foci leads to the formation of osteochondromas that are identical pathologically and radiographically in all respects to other exostoses. The prevalence of development of osteochondroma in various studies of irradiated patients ranges from 6% to 24% (10–15), with the largest series reporting the lower frequency (15). Osteochondromas represent the most common benign radiation-induced tumor, and such lesions were first reported in 1950 (16). Radiation-induced osteochondroma occurs most frequently in patients who undergo radiation therapy for neuroblastoma or Wilms tumor between the ages of 8 months and 11 years (11–15). In these cases, radiation dose is usually 1,500–5,500 cGy, although Neuhauser and coworkers (17) reported a case that developed after a single dose of 125 cGy (12–17). The latent period before discovery of the osteochondroma following radiation treatment is 3–17 years (mean, 5–12 years) (11–15). Lesions can occur anywhere in the radiation field and may have a higher prevalence with total body irradiation as opposed to localized irradiation (14). Other skeletal manifestations of irradiation may be apparent (scoliosis, atrophy, radiation necrosis), and in rare cases, malignant transformation of a radiation-induced osteochondroma to chondrosarcoma has been reported (2,18).

At gross examination, the cartilage cap of an osteochondroma has a bosselated, shiny, and glistening, bluish-gray surface, reminiscent of cauliflower (Fig 3a). Osteochondromas vary dramatically in size but are usually between 1 and 10 cm. The thickness of the cartilage cap is typically 1–3 cm in young patients, whereas in adults it is often only a few millimeters thick or entirely absent, leaving a surface composed of eburnated bone (1,2,19–23). The hyaline cartilage cap is also usually undulating and lobulated, with areas that invaginate into the underlying medullary component of the lesions (Fig 3a, 3b). On cut sections, the cartilage cap often appears with opaque yellow-to-gray areas due to calcification within the cartilage matrix.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.   Resected solitary benign osteochondroma. (a, b) Photographs of coronally sectioned gross specimen (a) and coronally sectioned whole mount specimen (hematoxylin-eosin [H-E] stain) (b) show yellow marrow in the lesion (*) and blue hyaline cartilage cap (arrowheads). There is undulation of the hyaline cartilage that invaginates in several areas into the medullary component (straight arrows) of the osteochondroma. (c) Photomicrograph (original magnification, x250; H-E stain) reveals yellow marrow (*) and trabeculae (straight arrows) within the osteochondroma, the hyaline cartilage cap with columns of cartilage cells (arrowheads), and fibrous capsule or perichondrium (curved arrows in b and c).

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.   Resected solitary benign osteochondroma. (a, b) Photographs of coronally sectioned gross specimen (a) and coronally sectioned whole mount specimen (hematoxylin-eosin [H-E] stain) (b) show yellow marrow in the lesion (*) and blue hyaline cartilage cap (arrowheads). There is undulation of the hyaline cartilage that invaginates in several areas into the medullary component (straight arrows) of the osteochondroma. (c) Photomicrograph (original magnification, x250; H-E stain) reveals yellow marrow (*) and trabeculae (straight arrows) within the osteochondroma, the hyaline cartilage cap with columns of cartilage cells (arrowheads), and fibrous capsule or perichondrium (curved arrows in b and c).

View larger version (173K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.   Resected solitary benign osteochondroma. (a, b) Photographs of coronally sectioned gross specimen (a) and coronally sectioned whole mount specimen (hematoxylin-eosin [H-E] stain) (b) show yellow marrow in the lesion (*) and blue hyaline cartilage cap (arrowheads). There is undulation of the hyaline cartilage that invaginates in several areas into the medullary component (straight arrows) of the osteochondroma. (c) Photomicrograph (original magnification, x250; H-E stain) reveals yellow marrow (*) and trabeculae (straight arrows) within the osteochondroma, the hyaline cartilage cap with columns of cartilage cells (arrowheads), and fibrous capsule or perichondrium (curved arrows in b and c).

	Solitary Osteochondroma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Solitary osteochondroma is a frequent lesion estimated to occur in 1%–2% of individuals undergoing extensive radiographic evaluation (1–4,25,26). These lesions constitute 20%–50% of benign bone tumors and 10%–15% of all bone tumors (2,25,26). The vast majority of solitary osteochondromas are asymptomatic and, if detected, are found incidentally (25,26). Symptomatic lesions usually occur in younger patients, with 75%–80% of such cases being discovered before the age of 20 years (1–4,25,26). Solitary osteochondroma has a male predilection, ranging from 1.6–3.4 to 1 (25).

The most common symptom related to osteochondroma is a nontender, painless cosmetic deformity related to the slowly enlarging exophytic mass. Additional complications that cause symptoms include osseous deformity, fracture, vascular compromise, neurologic sequelae, overlying bursa formation, and malignant transformation (27).

Any bone that develops from preformed cartilage (enchondral ossification) may develop an osteochondroma. The long bones of the lower extremity are most frequently affected (50% of cases) and are more commonly involved than those of the upper extremity by a ratio of 2 to 1 (1–4,25,26). As with other bone tumors, osteochondromas occur most often about the knee (40% of cases) (2,22,25). The femur is the single most frequently affected bone (30% of cases), with distal involvement being three times more common than proximal involvement (25). Tibial osteochondromas account for 15%–20% of cases and most commonly occur in a proximal location (2,22,25). The humerus is also a frequent site of osteochondromas (10%–20% of cases) (2,25,26). Other more unusual locations of osteochondroma include small bones of the hands and feet (10% of cases), scapula (4%), pelvis (5%), and spine (2%) (2,22,25,26). Long bone lesions frequently affect the metaphysis, with the diaphysis being a rare location.

The radiographic appearance of solitary osteochondroma, particularly in long bones, is frequently pathognomonic. The lesion is composed of cortical and medullary bone protruding from and continuous with the underlying bone (Figs 4, 5). The areas of osseous continuity between parent bone and osteochondroma may be broad, involving a large portion of the bone circumference (dimension of the lesion base exceeding its length—sessile osteochondroma), or narrow, with a bulbous tip (pedunculated osteochondroma). Identifying the characteristic cortical and medullary continuity between lesion and parent bone on radiographs is dependent on lesion type (sessile or pedunculated), location, and image projection. This relationship is usually well delineated in lesions of long bones, particularly pedunculated osteochondromas, with standard radiographic projections (although often only on one view) (Fig 6). However, in osteochondromas of flat bones with complex anatomy (ie, pelvis, spine, scapula) and sessile lesions, the continuity and thus the diagnosis may not be apparent on radiographs alone (Fig 7). Pedunculated lesions usually point away from the nearest joint owing to the forces of the overlying tendons and ligaments (although not typically attached to the osteochondroma).

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (124K): [in this window] [in a new window] [Download PPT slide]   Figure 4d.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 4e.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (86K): [in this window] [in a new window] [Download PPT slide]   Figure 4f.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 4g.   Benign solitary osteochondroma of the tibia in a 15-year-old boy with lesion growth. (a) Initial lateral radiograph of the ankle shows pathognomonic features of osteochondroma with a lesion composed of cortical and medullary bone protruding from the underlying tibia (open arrow). The cortical (solid arrows) and medullary (*) continuity with the tibia was seen on radiographs only in the lateral projection. The cartilage cap is not mineralized and cannot be seen. (b-d) Axial MR images (repetition time msec/echo time msec = 600/16) obtained before (b) and after (c) intravenous administration of gadolinium-based contrast material also reveal the cortical (arrowheads) and marrow (*) continuity with the underlying bone and yellow marrow in the lesion. The hyaline cartilage cap is 3 cm thick (curved arrows), shows mild peripheral and septal contrast material enhancement (straight arrows), and becomes very high signal intensity on the sagittal short-inversion-time inversion recovery (3,000/17, 90 msec inversion time) MR image (d). (e) Lateral radiograph obtained 2 years later shows lesion growth and mineralization that simulate malignant transformation but represent only growth in the skeletally immature patient. (f) Bone scan demonstrates marked increased uptake of radionuclide. (g) Photograph of the sagittally sectioned specimen correlates with the imaging appearance, revealing yellow marrow (*) and the thick hyaline cartilage cap (arrows). Foci of mineralization (x) are also seen, as noted previously in the MR images (b-d).

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 5d.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (170K): [in this window] [in a new window] [Download PPT slide]   Figure 5e.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 5f.   Benign solitary sessile osteochondroma of the fibula in a 19-year-old man. (a-e) Radiograph (a), axial CT scans (bone [b] and soft-tissue [c] windows), and axial T1-weighted (500/20) (d) and T2-weighted (2,000/90) (e) MR images show the marrow and cortical continuity of an osteochondroma and underlying fibula (large arrowheads). The various degrees of maturity and calcification in the areas of enchondral mineralization cause a heterogeneous appearance on CT and MR images and can be seen in the photograph of the axially sectioned gross specimen (f). Mature areas of bone formation contain yellow marrow architecture (*). Areas of calcified cartilage show high attenuation on CT scans (solid arrows in b and c), are white in the gross specimen (curved arrows), but are very heterogeneous on T2-weighted MR images (low signal intensity with all pulse sequences in densely calcified areas [small arrowheads in d and e] versus higher signal intensity in areas with more prominent components of nonmineralized cartilage [solid arrows in e]). Nonmineralized hyaline cartilage cap (open arrows) is thin (1 cm) and has more fluid characteristic at CT and MR imaging, reflecting its high water content, and has a blue color on the gross specimen. It is more difficult to detect on the soft-tissue window CT scan (c) than with MR imaging.

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.   Solitary benign pedunculated osteochondroma of the femur in a 22-year-old man with an associated fracture. (a) Radiograph of the knee reveals a pedunculated osteochondroma with marrow and cortical continuity to the underlying femur (arrowheads). The lesion points away from the knee joint and a lucent area at the base represents a fracture (arrow). (b) Sonogram shows posterior acoustic shadowing from the ossified lesion component and small thin hypoechoic hyaline cartilage cap (*), both of which are easily distinguished from the more superficial hyperechoic fat and muscle. (c) Photograph of the coronally sectioned whole-mount specimen (H-E stain) shows the cortex (open arrows), yellow marrow space (solid arrows), cartilage cap (*), and a portion of the healing fracture (arrowheads).

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.   Solitary benign pedunculated osteochondroma of the femur in a 22-year-old man with an associated fracture. (a) Radiograph of the knee reveals a pedunculated osteochondroma with marrow and cortical continuity to the underlying femur (arrowheads). The lesion points away from the knee joint and a lucent area at the base represents a fracture (arrow). (b) Sonogram shows posterior acoustic shadowing from the ossified lesion component and small thin hypoechoic hyaline cartilage cap (*), both of which are easily distinguished from the more superficial hyperechoic fat and muscle. (c) Photograph of the coronally sectioned whole-mount specimen (H-E stain) shows the cortex (open arrows), yellow marrow space (solid arrows), cartilage cap (*), and a portion of the healing fracture (arrowheads).

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.   Solitary benign pedunculated osteochondroma of the femur in a 22-year-old man with an associated fracture. (a) Radiograph of the knee reveals a pedunculated osteochondroma with marrow and cortical continuity to the underlying femur (arrowheads). The lesion points away from the knee joint and a lucent area at the base represents a fracture (arrow). (b) Sonogram shows posterior acoustic shadowing from the ossified lesion component and small thin hypoechoic hyaline cartilage cap (*), both of which are easily distinguished from the more superficial hyperechoic fat and muscle. (c) Photograph of the coronally sectioned whole-mount specimen (H-E stain) shows the cortex (open arrows), yellow marrow space (solid arrows), cartilage cap (*), and a portion of the healing fracture (arrowheads).

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.   Solitary benign osteochondroma of the pelvis in a 70-year-old man with vague hip pain. (a) Pelvic radiograph shows nonspecific sclerosis over the right supraacetabular region (arrow). Bone scan (not shown) revealed only mild radionuclide uptake. (b) CT scan reveals an osteochondroma with characteristic marrow (*) and cortical (arrowheads) continuity. The overlying soft-tissue attenuation could simulate a thick nonmineralized cartilage cap (arrows) and the possibility of malignant transformation. However, this finding represents iliacus muscle draped over the osteochondroma rather than a cartilage cap. (c) Photograph of a coronally sectioned whole-mount specimen reveals the cortical (solid arrows) and medullary (*) continuity with the underlying parent bone and lack of significant cartilage cap (open arrow).

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.   Solitary benign osteochondroma of the pelvis in a 70-year-old man with vague hip pain. (a) Pelvic radiograph shows nonspecific sclerosis over the right supraacetabular region (arrow). Bone scan (not shown) revealed only mild radionuclide uptake. (b) CT scan reveals an osteochondroma with characteristic marrow (*) and cortical (arrowheads) continuity. The overlying soft-tissue attenuation could simulate a thick nonmineralized cartilage cap (arrows) and the possibility of malignant transformation. However, this finding represents iliacus muscle draped over the osteochondroma rather than a cartilage cap. (c) Photograph of a coronally sectioned whole-mount specimen reveals the cortical (solid arrows) and medullary (*) continuity with the underlying parent bone and lack of significant cartilage cap (open arrow).

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.   Solitary benign osteochondroma of the pelvis in a 70-year-old man with vague hip pain. (a) Pelvic radiograph shows nonspecific sclerosis over the right supraacetabular region (arrow). Bone scan (not shown) revealed only mild radionuclide uptake. (b) CT scan reveals an osteochondroma with characteristic marrow (*) and cortical (arrowheads) continuity. The overlying soft-tissue attenuation could simulate a thick nonmineralized cartilage cap (arrows) and the possibility of malignant transformation. However, this finding represents iliacus muscle draped over the osteochondroma rather than a cartilage cap. (c) Photograph of a coronally sectioned whole-mount specimen reveals the cortical (solid arrows) and medullary (*) continuity with the underlying parent bone and lack of significant cartilage cap (open arrow).

Bone scintigraphy of osteochondromas varies and is directly correlated with the degree of enchondral bone formation (23,26,28–30). As such, there is generally more prominent radionuclide uptake in osteochondromas in younger patients, although this increased activity often persists well beyond the time of skeletal maturity (Fig 4f). Osteochondromas without increased radionuclide uptake (quiescent lesions) are more frequent in older patients (23).

The three-dimensional imaging capability of CT often allows optimal depiction of the pathognomonic cortical and marrow continuity of the lesion and parent bone in osteochondromas (21,23,31–34). This is particularly true for lesions in complex areas of anatomy, such as the pelvis or spine, and for those with a broad stalk of attachment. In fact, in our opinion, very thin sections available with CT are often superior to MR imaging in these cases. Measurement of hyaline cartilage cap thickness with CT has met with more variable success in the literature (19,21,31). Mineralization in the cartilage cap allows very accurate measurement with CT. However, it can be very difficult to accurately measure the thickness of an entirely nonmineralized cartilage cap because it cannot be easily differentiated from surrounding muscle or bursa (Figs 5, 7). In fact, Hudson and coworkers (31) believed CT did not reliably depict cartilage caps less than 2.5 cm in maximum thickness. In our opinion, CT is usually accurate in measuring cartilage cap thickness, and we suggest that previous studies were relatively early in experience with musculoskeletal CT. The nonmineralized areas of cartilage cap are often lower in attenuation than muscle, corresponding to its high water content (75%–80%) (Fig 5). The cartilage cap in benign osteochondromas in studies by Kenney et al (21) and Hudson et al (31) averaged 6 mm and 8 mm, with a maximum of 2.5 cm. It is vital to emphasize that the hyaline cartilage cap thickness is significantly dependent on the degree of skeletal maturity. Increased thickness of the cartilage cap is a recognized feature in young patients in response to continued active growth and should not be viewed as a finding of malignant transformation in skeletally immature patients (Fig 4).

US also enables accurate measurement of the thickness of the hyaline cartilage cap thickness (19,31,35). In a study by Malghem and coworkers (19), US revealed a mean measurement error of less than 2 mm, with hyaline cartilage cap thickness less than 2 cm. In this study, US was more accurate than CT and similar to MR imaging in evaluation of cartilage cap thickness. US allows surrounding fat (hyperechoic) and muscle to be easily distinguished from the nonmineralized cartilage cap, which appears as a hypoechoic layer (Fig 6b). Areas of mineralization in the cartilage cap and the underlying osseous component show posterior acoustic shadowing. Disadvantages of US include operator dependence, inability to evaluate deep lesions inaccessible to the probe, and lack of evaluation of the osseous components of the lesion.

MR imaging also demonstrates cortical and medullary continuity between the osteochondroma and parent bone (Figs 4, 5), and this distinctive feature is often better seen with this modality as opposed to radiography in complex areas of anatomy. Cortical bone is devoid of mobile protons and remains low signal intensity with all pulse sequences, whereas the medullary component has an appearance of yellow marrow. MR imaging is the best radiologic modality for visualizing the effect of the lesion on surrounding structures and evaluating the hyaline cartilage cap. Mineralized areas in the cartilage cap remain low signal intensity with all MR pulse sequences, although as enchondral ossification proceeds, yellow marrow signal is ultimately apparent. The high water content in nonmineralized portions of the cartilage cap had intermediate to low signal intensity on T1-weighted images and very high signal intensity on T2-weighted MR images (19,36–38) (Figs 4, 5). These features typically allow accurate measurement of the cartilage cap thickness and distinction from overlying muscle on MR images. However, in young patients with active growth and maturation from normal enchondral ossification in the cartilage cap, there may be marked heterogeneity with all MR pulse sequences from the mixture of these tissues (nonmineralized cartilage, calcified cartilage, and ossification with yellow marrow). Low signal intensity at the periphery of the lesion represents the perichondrium (36). Enhancement after the intravenous administration of gadolinium-based contrast material reveals septal and peripheral enhancement in the cartilage cap (37–40) (Fig 4c).

	Hereditary Multiple Exostoses

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
HME, also known as familial osteochondromatosis or diaphyseal aclasis, is characterized by the development of multiple osteochondromas (1,2). HME was differentiated from the solitary form of osteochondroma in 1786, with the earliest known description of an afflicted family reported by Boyer in 1814 (41). The estimated prevalence of HME is 1:50,000 to 1:100,000 in Western populations (42–45) and may be as high as 1:1,000 in the Chamorros, the indigenous people of Guam and the Mariana Islands (42,46).

The number of exostoses, the degree and type of angular deformity, and even the rate of malignant transformation vary significantly in HME, even within families. The disease shows an autosomal dominant inheritance pattern, with incomplete penetrance in females (47,48). Approximately two-thirds of affected individuals have a positive family history (49). The specific genetic abnormalities have recently been detected, with three distinct loci: one each on chromosomes 8, 11, and 19 (49–52).

The genetic basis for HME stems from the identification of similar osseous changes in Langer-Giedion syndrome, a contiguous gene syndrome that maps to chromosome band 8q24.1 (53,54). This observation suggests that the gene involved in HME also maps to this region and is responsible for the skeletal changes in Langer-Giedion syndrome (42,53,54). Genetic linkage analysis of this region confirms the presence of a locus for HME as being EXT1 on chromosome 8, and additional loci on chromosomes 11 and 19, designated as EXT2 and EXT3 (42,52–55).

Sequence analysis of the EXT loci in patients with HME has suggested that the EXT genes on chromosomes 8, 11, and 19 (49,52–55) function as tumor suppressor sites. These observations have also suggested a model in which inactivation of EXT genes leads to formation of an exostosis, with subsequent inactivation of a second EXT gene (or possibly another gene) causing malignant transformation (48,49,51–55). Recent genetic studies have suggested that three phenotypic patterns exist for HME and correlate with the three genotypes (49). Males are affected approximately 1.5 times more commonly than females (48). The observation of unequal sex ratios, with a significant male preponderance, supports the concept of incomplete penetrance in females (48). This incomplete penetrance may be the result of hormonal factors or perhaps an X-linked modifying gene (48).

The multiplicity of lesions and associated deformity, particularly with severe involvement, lead to early radiologic evaluation and diagnosis of HME, in contrast to the relatively later diagnosis of solitary osteochondromas (49). In fact, the diagnosis of HME is made at birth in some cases (48,49). Most patients are diagnosed by age 5 years, and virtually all are diagnosed by age 12 years (2,49). In families with the genetic predisposition, members who do not demonstrate lesions by age 12 years will not manifest the disease (48,49).

The skeletal distribution of lesions varies, with some authors noting that the typical distribution is bilateral and symmetric, whereas others report a strong unilateral predominance (2,49). This difference may relate to the genetic type of HME, as Carroll and coworkers (49) have noted asymmetric involvement in two of the three genotypes. Nearly every bone, with the exception of the calvaria (above the skull base), has been described as being involved in HME. Specific sites of involvement include the scapula and ribs (40% of cases), humerus (50%–98%), elbow (35%–40%), wrist (30%–60%), hands (20%–30%), pelvis (5%–15%), hips (30%–90%), knees (70%–98%), ankles (25%–54%), and feet (10%–25%) (2,25,26,56) (Fig 8).

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.   Manifestations of HME in three patients. (a) Photograph of a 30-year-old patient with HME demonstrates marked forearm abnormalities and milder knee and ankle valgus deformities that result in a mild short stature. (b-d) Pelvic (b), lower extremity (c), and hand (d) radiographs of an 8-year-old patient show extensive undertubulation with widened metaphyses (Erlenmeyer flask deformity). These growth disturbances are much more apparent than the pelvic osteochondromas. Coxa and genu valgus, lateral ankle tilt (arrowhead), extrinsic erosion of the left fibula by the tibial osteochondroma (straight arrow), and osseous bowing of the radius with pseudo-Madelung (curved arrow) deformities are also seen. (e) Photograph of a coronally sectioned whole-mount specimen (H-E stain) from a 9-year-old patient reveals multiple osteochondromas involving the femur. The largest lesion medially shows characteristic medullary and cortical continuity (solid arrows) with the underlying parent bone as well as the overlying hyaline cartilage cap and perichondrium (open arrow). Yellow marrow within the lesion (M), undertubulation of bone with Erlenmeyer flask deformity (*), and multiple smaller lesions (arrowheads) are also seen.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.   Manifestations of HME in three patients. (a) Photograph of a 30-year-old patient with HME demonstrates marked forearm abnormalities and milder knee and ankle valgus deformities that result in a mild short stature. (b-d) Pelvic (b), lower extremity (c), and hand (d) radiographs of an 8-year-old patient show extensive undertubulation with widened metaphyses (Erlenmeyer flask deformity). These growth disturbances are much more apparent than the pelvic osteochondromas. Coxa and genu valgus, lateral ankle tilt (arrowhead), extrinsic erosion of the left fibula by the tibial osteochondroma (straight arrow), and osseous bowing of the radius with pseudo-Madelung (curved arrow) deformities are also seen. (e) Photograph of a coronally sectioned whole-mount specimen (H-E stain) from a 9-year-old patient reveals multiple osteochondromas involving the femur. The largest lesion medially shows characteristic medullary and cortical continuity (solid arrows) with the underlying parent bone as well as the overlying hyaline cartilage cap and perichondrium (open arrow). Yellow marrow within the lesion (M), undertubulation of bone with Erlenmeyer flask deformity (*), and multiple smaller lesions (arrowheads) are also seen.

View larger version (93K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.   Manifestations of HME in three patients. (a) Photograph of a 30-year-old patient with HME demonstrates marked forearm abnormalities and milder knee and ankle valgus deformities that result in a mild short stature. (b-d) Pelvic (b), lower extremity (c), and hand (d) radiographs of an 8-year-old patient show extensive undertubulation with widened metaphyses (Erlenmeyer flask deformity). These growth disturbances are much more apparent than the pelvic osteochondromas. Coxa and genu valgus, lateral ankle tilt (arrowhead), extrinsic erosion of the left fibula by the tibial osteochondroma (straight arrow), and osseous bowing of the radius with pseudo-Madelung (curved arrow) deformities are also seen. (e) Photograph of a coronally sectioned whole-mount specimen (H-E stain) from a 9-year-old patient reveals multiple osteochondromas involving the femur. The largest lesion medially shows characteristic medullary and cortical continuity (solid arrows) with the underlying parent bone as well as the overlying hyaline cartilage cap and perichondrium (open arrow). Yellow marrow within the lesion (M), undertubulation of bone with Erlenmeyer flask deformity (*), and multiple smaller lesions (arrowheads) are also seen.

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.   Manifestations of HME in three patients. (a) Photograph of a 30-year-old patient with HME demonstrates marked forearm abnormalities and milder knee and ankle valgus deformities that result in a mild short stature. (b-d) Pelvic (b), lower extremity (c), and hand (d) radiographs of an 8-year-old patient show extensive undertubulation with widened metaphyses (Erlenmeyer flask deformity). These growth disturbances are much more apparent than the pelvic osteochondromas. Coxa and genu valgus, lateral ankle tilt (arrowhead), extrinsic erosion of the left fibula by the tibial osteochondroma (straight arrow), and osseous bowing of the radius with pseudo-Madelung (curved arrow) deformities are also seen. (e) Photograph of a coronally sectioned whole-mount specimen (H-E stain) from a 9-year-old patient reveals multiple osteochondromas involving the femur. The largest lesion medially shows characteristic medullary and cortical continuity (solid arrows) with the underlying parent bone as well as the overlying hyaline cartilage cap and perichondrium (open arrow). Yellow marrow within the lesion (M), undertubulation of bone with Erlenmeyer flask deformity (*), and multiple smaller lesions (arrowheads) are also seen.

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 8e.   Manifestations of HME in three patients. (a) Photograph of a 30-year-old patient with HME demonstrates marked forearm abnormalities and milder knee and ankle valgus deformities that result in a mild short stature. (b-d) Pelvic (b), lower extremity (c), and hand (d) radiographs of an 8-year-old patient show extensive undertubulation with widened metaphyses (Erlenmeyer flask deformity). These growth disturbances are much more apparent than the pelvic osteochondromas. Coxa and genu valgus, lateral ankle tilt (arrowhead), extrinsic erosion of the left fibula by the tibial osteochondroma (straight arrow), and osseous bowing of the radius with pseudo-Madelung (curved arrow) deformities are also seen. (e) Photograph of a coronally sectioned whole-mount specimen (H-E stain) from a 9-year-old patient reveals multiple osteochondromas involving the femur. The largest lesion medially shows characteristic medullary and cortical continuity (solid arrows) with the underlying parent bone as well as the overlying hyaline cartilage cap and perichondrium (open arrow). Yellow marrow within the lesion (M), undertubulation of bone with Erlenmeyer flask deformity (*), and multiple smaller lesions (arrowheads) are also seen.

Taniguchi (43) reviewed 41 children with HME and devised a practical classification system, dividing them into three groups based on the extent of forearm involvement: group I, with no involvement of the distal forearm; group II, with involvement of the distal forearm, but without shortening of the radius or ulna; and group III, with involvement of the distal forearm and shortening of the distal radius or ulna. Children in group I were mildly affected and presented at an older age, whereas those in group III were severely affected, presented at a much earlier age, and were more likely to experience malignant transformation.

Short stature is a frequent clinical feature (40% of cases) that may be the result of the development of exostoses during childhood and early puberty, at the expense of longitudinal bone growth (42). As would be expected, childhood height is correlated with severity of involvement (43) (Fig 8).

	Complications of Osteochondroma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Complications and their imaging appearances associated with HME and solitary osteochondroma are identical. However, the prevalence of these manifestations in HME is greater owing to the multiplicity of lesions.

	Cosmetic and Osseous Deformity

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Cosmetic deformity caused by an underlying exostosis is the most common clinical presentation of osteochondroma and frequently leads to surgical resection (1–4). Bone deformity includes both growth sequelae as a result of a failure of normal tubulation and local effects such as osseous bowing and malalignment. Both abnormalities are much more frequently associated with and extensive in HME. In fact, in very young patients, the undertubulation of bone in the metaphyses about the hip and knee may be the first radiographic manifestation of disease prior to mineralization and visualization of individual osteochondromas. Radiographs reveal a widened metadiaphyseal junction and in the distal femur an Erlenmeyer flask deformity may be apparent (Fig 8). The most common osseous deformities associated with HME and their prevalences are shown in the Table, and they affect the knee, hip, and ankle in order of decreasing frequency (Fig 8).

A radiographic skeletal survey to effectively screen for the presence of HME should consist of radiographs of long bones (femora, tibiae, humeri, forearms), chest, and pelvis to identify and quantify underlying deformity. Complete radiographic evaluation of areas with significant deformity may then be performed, particularly the hips, knees, ankles, and wrists.

Fracture
Fracture of an osteochondroma is an unusual complication resulting from localized trauma and typically involves the base of the lesion stalk (27,57,58). Pedunculated osteochondromas about the knee are most likely to demonstrate associated fracture with linear lucency and cortical angulation near the region of continuity with the underlying bone (Fig 6). Subsequently, callus formation causing bandlike sclerosis on radiographs occurs with healing. No significant incidence of nonunion has been reported. Interestingly, regression or resorption of solitary osteochondroma occurring both spontaneously and following a fracture has been reported (59–62).

Vascular Compromise
Vascular complications associated with osteochondroma include vessel displacement, stenosis, occlusion, and pseudoaneurysm formation (63–76). Displacement of adjacent vessels by these lesions is common, particularly when they are large, but it is typically asymptomatic. Clinical symptoms in cases of vascular compromise include pain, swelling, and rarely claudication or a palpable pulsatile mass usually affecting a young patient. Vascular thrombosis or occlusion may affect either the arterial or venous system and is most frequently seen in the vessels about the knee, particularly the popliteal artery or vein (63–68).

Pseudoaneurysm formation associated with osteochondroma was first reported by Paul (77) in 1953. Although described arterial locations include the superficial femoral, brachial, and posterior tibial arteries, the popliteal artery is most frequently involved (69–77) (Fig 9). This complication affects young patients near the end of normal skeletal growth and occurs with solitary and multiple lesions with equal frequency. It has been hypothesized that during this time the cartilage cap matures, undergoing ossification and converting a relatively soft surface to a firm, often sharp area (69–75). Osteochondromas lying adjacent to an artery can chronically abrade and ultimately lacerate the arterial surface with normal movement or repetitive trauma. The predominance of popliteal artery involvement is related to the frequency of osteochondromas in this location as well as to the fixed position of this vessel proximally at the adductor canal and distally by its branches. This lack of mobility of the popliteal artery does not allow the vessel to displace, but instead it becomes tethered over the osteochondroma.

View larger version (155K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.   Solitary benign osteochondroma with a popliteal pseudoaneurysm in a 13-year-old boy. Axial fat-suppressed gadolinium-enhanced T1-weighted (800/17) (a) and sagittal T2-weighted (5,000/120) (b) MR images and contrast material-enhanced axial CT scan (c) with sagittal reconstruction (d) show an osteochondroma containing yellow marrow and continuity with the underlying femur (large arrowheads). The large complex mass posterior to the osteochondroma (*) and containing the popliteal artery (arrow) just below the adductor canal represents a pseudoaneurysm. The pseudoaneurysm does not diffusely enhance with contrast material owing to thrombus as suggested by the concentric rings (small arrowheads) on the T2-weighted MR image (b). (Courtesy of Sergio Brincas, MD, Hospital de Caridade, Florianopolis, Brazil.)

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.   Solitary benign osteochondroma with a popliteal pseudoaneurysm in a 13-year-old boy. Axial fat-suppressed gadolinium-enhanced T1-weighted (800/17) (a) and sagittal T2-weighted (5,000/120) (b) MR images and contrast material-enhanced axial CT scan (c) with sagittal reconstruction (d) show an osteochondroma containing yellow marrow and continuity with the underlying femur (large arrowheads). The large complex mass posterior to the osteochondroma (*) and containing the popliteal artery (arrow) just below the adductor canal represents a pseudoaneurysm. The pseudoaneurysm does not diffusely enhance with contrast material owing to thrombus as suggested by the concentric rings (small arrowheads) on the T2-weighted MR image (b). (Courtesy of Sergio Brincas, MD, Hospital de Caridade, Florianopolis, Brazil.)

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.   Solitary benign osteochondroma with a popliteal pseudoaneurysm in a 13-year-old boy. Axial fat-suppressed gadolinium-enhanced T1-weighted (800/17) (a) and sagittal T2-weighted (5,000/120) (b) MR images and contrast material-enhanced axial CT scan (c) with sagittal reconstruction (d) show an osteochondroma containing yellow marrow and continuity with the underlying femur (large arrowheads). The large complex mass posterior to the osteochondroma (*) and containing the popliteal artery (arrow) just below the adductor canal represents a pseudoaneurysm. The pseudoaneurysm does not diffusely enhance with contrast material owing to thrombus as suggested by the concentric rings (small arrowheads) on the T2-weighted MR image (b). (Courtesy of Sergio Brincas, MD, Hospital de Caridade, Florianopolis, Brazil.)

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 9d.   Solitary benign osteochondroma with a popliteal pseudoaneurysm in a 13-year-old boy. Axial fat-suppressed gadolinium-enhanced T1-weighted (800/17) (a) and sagittal T2-weighted (5,000/120) (b) MR images and contrast material-enhanced axial CT scan (c) with sagittal reconstruction (d) show an osteochondroma containing yellow marrow and continuity with the underlying femur (large arrowheads). The large complex mass posterior to the osteochondroma (*) and containing the popliteal artery (arrow) just below the adductor canal represents a pseudoaneurysm. The pseudoaneurysm does not diffusely enhance with contrast material owing to thrombus as suggested by the concentric rings (small arrowheads) on the T2-weighted MR image (b). (Courtesy of Sergio Brincas, MD, Hospital de Caridade, Florianopolis, Brazil.)

Neurologic Sequelae
Neurologic compromise can be associated with both peripheral and central (vertebral or skull base) osteochondromas. Peripheral lesions may compress nerves, leading to entrapment neuropathy (including foot-drop), and peroneal nerve involvement from fibular osteochondroma has been reported most frequently (78,79). Radial nerve involvement has also been described (80). Imaging findings reflect the osteochondroma with mass effect in the expected nerve location, but the nerve itself is usually too small to discern. In addition, muscle atrophy with increased fat (caused by chronic entrapment) may be seen in the expected nerve distribution and is usually best depicted by MR imaging.

Central osteochondromas involving the skull base, spine, or rib heads may cause cranial nerve deficits, radiculopathy, spinal stenosis, cauda equina syndrome, and myelomalacia (81–92). Spinal osteochondromas account for 1%–4% of solitary lesions and are seen in 1%–9% of patients with HME (81–89,93). Interestingly, in patients with HME, spinal lesions are usually solitary. The cervical spine is most frequently affected (50% of lesions), with a particular predilection for C2, followed by the thoracic spine (most commonly T8, followed by T4) and the lumbar spine (81–85). Lesions that protrude dorsally from the posterior vertebral elements (lamina or spinous process) are typically large and manifest at an earlier age with cosmetic deformity and palpable mass but lack neurologic symptoms. In contradistinction, osteochondromas that extend into the spinal canal are often small but are associated with neurologic symptoms (Fig 10). Osteochondromas that extend anteriorly from the vertebral body may produce symptoms of dysphagia, hoarseness, and vascular compromise. Myelopathic symptoms are associated with spinal osteochondromas in 34% of patients with solitary lesions and in 77% of patients with HME (94).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.   Cervical spine osteochondroma in an 11-year-old boy with radicular symptoms. Radiographs (not shown) were normal. (a) Axial CT scan shows the narrow stalk and cortical continuity (arrowheads) at the spinolaminar junction of C5, pathognomonic of an osteochondroma. The lesion protrudes into the spinal canal. (b) Sagittal T1-weighted (500/25) MR image reveals fat signal intensity simulating a lipomatous lesion (arrows) resulting from the yellow marrow in the osteochondroma, but the continuity with bone is not seen. (c) Photograph of the sectioned gross specimen shows marrow space of the osteochondroma (*) and the thin hyaline cartilage cap (arrow).

View larger version (178K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.   Cervical spine osteochondroma in an 11-year-old boy with radicular symptoms. Radiographs (not shown) were normal. (a) Axial CT scan shows the narrow stalk and cortical continuity (arrowheads) at the spinolaminar junction of C5, pathognomonic of an osteochondroma. The lesion protrudes into the spinal canal. (b) Sagittal T1-weighted (500/25) MR image reveals fat signal intensity simulating a lipomatous lesion (arrows) resulting from the yellow marrow in the osteochondroma, but the continuity with bone is not seen. (c) Photograph of the sectioned gross specimen shows marrow space of the osteochondroma (*) and the thin hyaline cartilage cap (arrow).

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.   Cervical spine osteochondroma in an 11-year-old boy with radicular symptoms. Radiographs (not shown) were normal. (a) Axial CT scan shows the narrow stalk and cortical continuity (arrowheads) at the spinolaminar junction of C5, pathognomonic of an osteochondroma. The lesion protrudes into the spinal canal. (b) Sagittal T1-weighted (500/25) MR image reveals fat signal intensity simulating a lipomatous lesion (arrows) resulting from the yellow marrow in the osteochondroma, but the continuity with bone is not seen. (c) Photograph of the sectioned gross specimen shows marrow space of the osteochondroma (*) and the thin hyaline cartilage cap (arrow).

Bursa Formation
In 1891, Orlow (96) originally described bursa formation between osteochondroma and surrounding soft tissue as "exostosis bursata." This complication occurred in 1.5% in a large review of osteochondromas (872 cases) reported by Unni (97). It is most frequently related to sites with motion where friction develops. The most common specific locations of this reactive bursa formation include the scapula (over 50% of cases), lesions about the hip (lesser trochanter), and shoulder (97–106) (Figs 11–13). These bursae are lined by synovium and may become inflamed, infected, or hemorrhagic. In addition, the bursa may contain chondral or fibrin bodies, and chondrometaplasia can occur within the synovial lining, leading to secondary synovial chondromatosis (98).

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.   Bursa formation overlying a scapular osteochondroma in a 20-year-old patient. (a-d) CT scans (bone [a] and soft-tissue [b] windows) and axial T1-weighted (640/20) (c) and T2-weighted (1,800/90) (d) MR images show a typical osteochondroma with continuity to the underlying scapula (arrow). However, the overlying component (*) is relatively thick and would be worrisome for malignant transformation if it represents a hyaline cartilage cap. (e) Intraoperative photograph shows tip of the osteochondroma (arrowhead) and overlying bursal sac (arrows) without a significant cartilage cap.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.   Bursa formation overlying a scapular osteochondroma in a 20-year-old patient. (a-d) CT scans (bone [a] and soft-tissue [b] windows) and axial T1-weighted (640/20) (c) and T2-weighted (1,800/90) (d) MR images show a typical osteochondroma with continuity to the underlying scapula (arrow). However, the overlying component (*) is relatively thick and would be worrisome for malignant transformation if it represents a hyaline cartilage cap. (e) Intraoperative photograph shows tip of the osteochondroma (arrowhead) and overlying bursal sac (arrows) without a significant cartilage cap.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 11c.   Bursa formation overlying a scapular osteochondroma in a 20-year-old patient. (a-d) CT scans (bone [a] and soft-tissue [b] windows) and axial T1-weighted (640/20) (c) and T2-weighted (1,800/90) (d) MR images show a typical osteochondroma with continuity to the underlying scapula (arrow). However, the overlying component (*) is relatively thick and would be worrisome for malignant transformation if it represents a hyaline cartilage cap. (e) Intraoperative photograph shows tip of the osteochondroma (arrowhead) and overlying bursal sac (arrows) without a significant cartilage cap.

View larger version (161K): [in this window] [in a new window] [Download PPT slide]   Figure 11d.   Bursa formation overlying a scapular osteochondroma in a 20-year-old patient. (a-d) CT scans (bone [a] and soft-tissue [b] windows) and axial T1-weighted (640/20) (c) and T2-weighted (1,800/90) (d) MR images show a typical osteochondroma with continuity to the underlying scapula (arrow). However, the overlying component (*) is relatively thick and would be worrisome for malignant transformation if it represents a hyaline cartilage cap. (e) Intraoperative photograph shows tip of the osteochondroma (arrowhead) and overlying bursal sac (arrows) without a significant cartilage cap.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 11e.   Bursa formation overlying a scapular osteochondroma in a 20-year-old patient. (a-d) CT scans (bone [a] and soft-tissue [b] windows) and axial T1-weighted (640/20) (c) and T2-weighted (1,800/90) (d) MR images show a typical osteochondroma with continuity to the underlying scapula (arrow). However, the overlying component (*) is relatively thick and would be worrisome for malignant transformation if it represents a hyaline cartilage cap. (e) Intraoperative photograph shows tip of the osteochondroma (arrowhead) and overlying bursal sac (arrows) without a significant cartilage cap.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.   Hereditary multiple exostoses and an overlying bursa containing debris in a 42-year-old man with apparent rapid enlargement of a femoral osteochondroma. (a, b) Axial T2-weighted MR image (5,650/112) (a) and sonogram (b) show a fluid-filled mass (large arrowheads) with multiple filling defects (small arrowheads). (c) Photograph of the gross specimen shows that the mass corresponds to a bursa (large arrows) with multiple osteochondral fragments (small arrows) over a femoral osteochondroma rather than malignant transformation as was suspected clinically.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.   Hereditary multiple exostoses and an overlying bursa containing debris in a 42-year-old man with apparent rapid enlargement of a femoral osteochondroma. (a, b) Axial T2-weighted MR image (5,650/112) (a) and sonogram (b) show a fluid-filled mass (large arrowheads) with multiple filling defects (small arrowheads). (c) Photograph of the gross specimen shows that the mass corresponds to a bursa (large arrows) with multiple osteochondral fragments (small arrows) over a femoral osteochondroma rather than malignant transformation as was suspected clinically.

View larger version (116K): [in this window] [in a new window] [Download PPT slide]   Figure 12c.   Hereditary multiple exostoses and an overlying bursa containing debris in a 42-year-old man with apparent rapid enlargement of a femoral osteochondroma. (a, b) Axial T2-weighted MR image (5,650/112) (a) and sonogram (b) show a fluid-filled mass (large arrowheads) with multiple filling defects (small arrowheads). (c) Photograph of the gross specimen shows that the mass corresponds to a bursa (large arrows) with multiple osteochondral fragments (small arrows) over a femoral osteochondroma rather than malignant transformation as was suspected clinically.

View larger version (123K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.   Solitary benign osteochondroma of the femur with small bursa and hyaline cartilage cap in a 13-year-old girl. Oblique coronal T2-weighted (2,500/80) (a) and fat-suppressed three-dimensional spoiled gradient-recalled (SPGR) (60/5; flip angle, 40°) (b) MR images show an osteochondroma with cortical and marrow continuity (arrowheads) to the underlying femur. The T2-weighted MR image (a) shows a thin band of high signal intensity at the lesion periphery (arrows) that could represent a cartilage cap or bursa. The SPGR MR image (b) allows distinction of these two possibilities with very thin high-signal-intensity cartilage cap caused by bound water (arrows) versus low-signal-intensity small bursa with free water (*). (Courtesy of David Disler, MD, St Mary's Hospital, Richmond, Va.)

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.   Solitary benign osteochondroma of the femur with small bursa and hyaline cartilage cap in a 13-year-old girl. Oblique coronal T2-weighted (2,500/80) (a) and fat-suppressed three-dimensional spoiled gradient-recalled (SPGR) (60/5; flip angle, 40°) (b) MR images show an osteochondroma with cortical and marrow continuity (arrowheads) to the underlying femur. The T2-weighted MR image (a) shows a thin band of high signal intensity at the lesion periphery (arrows) that could represent a cartilage cap or bursa. The SPGR MR image (b) allows distinction of these two possibilities with very thin high-signal-intensity cartilage cap caused by bound water (arrows) versus low-signal-intensity small bursa with free water (*). (Courtesy of David Disler, MD, St Mary's Hospital, Richmond, Va.)

On radiographs, a bursa appears as a soft-tissue mass overlying the osteochondroma; this mass may contain new areas of chondroid mineralization representing intrabursal fragments that can simulate a thick cartilage cap with growth—a characteristic suggestive of malignant transformation. US is particularly helpful in accessible lesions for distinguishing the anechoic bursal collection with posterior acoustic enhancement from the solid hypoechoic tissue of the underlying hyaline cartilage cap (Fig 12b) (19,98–106). Chondral or fibrinous bodies, if calcified, may be detected in the bursa with posterior acoustic shadowing on US scans (Fig 12b). At CT and MR imaging, the bursa appears as a fluid-filled mass (low attenuation on CT scans, homogeneous low signal intensity on T1-weighted images, and high signal intensity on T2-weighted images), and calcified or noncalcified chondral filling defects may also be apparent (Figs 11, 12). However, distinction from the underlying hyaline cartilage cap may be difficult, particularly if it is largely nonmineralized because of the high water content of both areas (Fig 11). Contrast enhancement patterns (peripheral and septal) may also be quite similar on CT and MR images. MR pulse sequences that allow differentiation of free water (bursa) from bound water (cartilage cap) such as magnetization transfer and fat-suppressed three-dimensional spoiled gradient-recalled (SPGR) sequences have been successfully employed to distinguish these two structures (107) (Fig 13). In addition, the morphology (identification of a neck) or known anatomic location (iliopsoas, pes anserine) of a bursa detected at CT, MR imaging, or US may be helpful.

Malignant Transformation
Malignant transformation, the most feared sequelae of osteochondroma, occurs in approximately 1% of solitary lesions and was first reported in 1886 (1,2,22,25,108–116). The prevalence of this complication is higher with HME and was previously reported to be seen in up to 25% of these patients (1,2). However, newer studies suggest a lower prevalence of approximately 3%–5% in patients with HME (109–112,117,118).

The loci on chromosomes 8 and 11 have been associated with malignant transformation when loss of heterozygosity occurs, a phenomenon not described for chromosome 19. The malignant transformation is almost invariably due to chondrosarcoma arising in the cartilage cap of the lesion, although in rare cases osteosarcoma is reported at the base of the osteochondroma stalk (113,114). Chondrosarcoma arising in an osteochondroma (also referred to as secondary or peripheral chondrosarcoma) accounts for 8% of all chondrosarcomas and is usually solitary and a low histologic grade (67%–85% of cases), although multifocal (with HME) and dedifferentiated lesions have also been reported (1,20,22,108,115,116,119). Lesions that grow or cause pain after skeletal maturity should be suspected of malignant transformation, since osteochondromas only rarely enlarge after this time (120). Centrally located osteochondromas about the pelvis, hips, and shoulders are particularly more prone to undergo malignant transformation. Malignant transformation typically develops at different ages, depending on whether it is associated with solitary osteochondroma (average age, 50–55 years) versus HME (average age, 25–30 years) (1,2,22). Malignant transformation before the age of 20 is distinctly unusual.

Imaging findings of chondrosarcoma have predominantly emphasized changes in appearance of the hyaline cartilage cap, reflecting that this region is the site of origin of the malignant transformation. Radiographic features that suggest malignancy include (a) growth of a previously unchanged osteochondroma in a skeletally mature patient, (b) irregular or indistinct lesion surface, (c) focal regions of radiolucency in the interior of the lesion, (d) erosion or destruction of the adjacent bone, and (e) a significant soft-tissue mass particularly containing scattered or irregular calcification (109–112,117,118) (Figs 14, 15).

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 14a.   Malignant transformation to chondrosarcoma of a solitary fibular osteochondroma in a 35-year-old man who presented with a progressively enlarging mass. (a) Radiographs of the knee show an osteochondroma involving the tibia (large arrows) with an indistinct peripheral margin (small arrows) and scattered calcifications (arrowheads). (b) Photograph of a coronally sectioned whole-mount specimen (H-E stain) reveals the osteochondroma with cortical and marrow (arrowheads) continuity to the underlying tibia. The 4-cm-thick hyaline cartilage cap (*) with areas of calcification (arrows) represents low-grade chondrosarcoma from malignant transformation.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 14b.   Malignant transformation to chondrosarcoma of a solitary fibular osteochondroma in a 35-year-old man who presented with a progressively enlarging mass. (a) Radiographs of the knee show an osteochondroma involving the tibia (large arrows) with an indistinct peripheral margin (small arrows) and scattered calcifications (arrowheads). (b) Photograph of a coronally sectioned whole-mount specimen (H-E stain) reveals the osteochondroma with cortical and marrow (arrowheads) continuity to the underlying tibia. The 4-cm-thick hyaline cartilage cap (*) with areas of calcification (arrows) represents low-grade chondrosarcoma from malignant transformation.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 15a.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 15c.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 15d.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 15e.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 15f.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 15g.   Malignant transformation to chondrosarcoma of an iliac osteochondroma in a 50-year-old man with HME. (a) Pelvic radiograph shows widened femoral metaphyses from tubulation abnormality associated with HME and calcification overlying and above the left iliac crest (arrows). (b-e) CT scan (b) and axial T1-weighted (500/16) (c), fat-suppressed gadolinium-enhanced T1-weighted (800/20) (d), and T2-weighted (3,216/68) (e) MR images show an osteochondroma of the left iliac crest with cortical and marrow continuity (arrows). There is a large associated overlying soft-issue mass (large arrowheads) containing multiple calcifications representing secondary chondrosarcoma arising from the cartilage cap. The high water content of this cartilaginous tissue is reflected in the low attenuation on the CT scan (b) and very high signal intensity on the T2-weighted MR image (e). Mild, predominantly peripheral and septal enhancement is seen after gadolinium administration (small arrowheads in d). (f, g) Photographs of coronally sectioned gross (f) and whole-mount (H-E stain) (g) specimens demonstrate the large soft-tissue component of the chondrosarcoma (arrows) adjacent to the iliac crest (*).

Hyaline cartilage cap thickness is an extremely important criterion in determining malignant transformation. The appearance and difficulties in measuring the cartilage cap at US, CT, or MR imaging have already been described. Two series have reported the cartilage cap thickness differences in benign osteochondromas (0.1–3.0 cm; average, 0.6–0.8 cm) and those with secondary chondrosarcoma (1.5–12 cm; average, 5.5–6.0 cm) (19,31). Therefore, in our opinion and experience, a cartilage cap more than 1.5 cm thick in a skeletally mature patient should be viewed with great suspicion of harboring malignant transformation (Figs 14, 15). The disparity between the cartilage cap thickness in benign versus malignant osteochondromas is even more prominent in the series by Malghem et al (19) and Hudson et al (31), with 81% (30 of 37 lesions) of benign exostoses having a cartilage cap of less than 1 cm thick compared with 81% of cases of malignant transformation (13 of 16 lesions) having a cartilage cap greater than 2 cm thick. Thus, only a very small number of benign lesions may be excised if this criterion were used, and, more important, no lesions with malignant transformation would be missed.

At pathologic analysis, malignant transformation of osteochondroma shows signs of active peripheral growth. This growth may be reflected by invasion of the surrounding soft tissue or permeation of the underlying cortex. At histologic analysis, fibrous bands between cartilage lobules, increased cellularity, and atypia including binucleate cells may be seen.

Miscellaneous Complications
Additional, rarely reported complications of osteochondromas include osteomyelitis, infarction of the cartilage cap or osseous component, muscle impingement, and hemarthrosis (1,2,122).

	Osteochondroma Treatment

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Treatment of osteochondroma is individualized, with small asymptomatic or minimally symptomatic lesions followed up and only supportive care provided. Larger symptomatic lesions may be resected at their base where there is continuity to underlying bone. Pedunculated lesions are more easily removed. The overall recurrence rate after resection has been estimated at 2% (123). It is important to entirely resect the overlying perichondrium because inadequate excision of this tissue significantly increases the risk of recurrence. Leakage of the often myxomatous cartilage tissue at surgery into the postoperative bed can also result in soft-tissue recurrence, although this is rare. Surgical resection of benign osteochondroma is not without complication, as reported by Wirganowicz and colleagues (124), and occurs in 13% of patients. These complications included neuropraxia, arterial laceration, compartment syndrome, and fracture.

Treatment of patients with HME is much more problematic and complex than that of patients with solitary osteochondromas. Surgical treatment is often directed to correct the associated deformities rather than restricted to the exostoses alone. Multiple surgical procedures are often performed in these patients, with an average of 2.7 per patient in the series by Shapiro et al (56). Patients with HME require continued surveillance both clinically and radiologically to evaluate progression of deformities and development of complications.

Malignant transformation of osteochondroma to chondrosarcoma is generally treated with wide surgical resection and limb salvage. As with other chondrosarcomas, radiation therapy and chemotherapy are usually not employed, except in cases of dedifferentiated tumors. MR imaging provides exquisite delineation of the lesion extent and mass effect on adjacent structures and is vital for staging prior to surgical resection, as shown by Wuisman et al (108), who detected medullary extension with MR imaging in 30% of their 45 cases of secondary chondrosarcoma arising in an osteochondroma. Because most of these lesions are low-grade chondrosarcomas, the overall prognosis is good, with long-term survival in 70%–90% of cases, although patients with dedifferentiated lesions have a worse prognosis (20,108). The local recurrence rate varies with the adequacy of the tumor margins, from 0%–15% in cases with wide resection to 57%–78% in cases with marginal or intralesional resection (20,108). Metastases are unusual, occurring in approximately 3%–7% of patients, and most commonly affect the lungs (20,108).

	Osteochondroma Variants

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
Subungual Exostosis
Subungual exostosis was originally described by Dupuytren (125) in 1847. It is a common lesion, sometimes referred to as Dupuytren exostosis, that shares some radiographic features with osteochondroma but pathologically represents a distinct entity. The lesion cause is unknown, although trauma and infection have been proposed. It is likely that infection is a result of the lesion rather than its cause and that these exostoses are related to trauma.

Subungual exostosis classically arises from the dorsal or dorsomedial aspect of the distal phalanx, with a variable relationship to the nail bed. This location may be related to the loose periosteum in this area, as opposed to the tightly adherent periosteum in the volar aspect of the toe and finger pads. The typical clinical appearance is that of a mass under or adjacent to the nail bed present for weeks to months. The lesion may be painful and show secondary overlying skin ulceration. A distinct preceding history of trauma, such as chronic and repetitive injury in athletes, is elicited in only 14%–25% of cases (126,127). Although some reports have noted a female predilection, most authors report an equal sex distribution. Patients are most commonly affected in the 2nd and 3rd decades of life, although the reported age range is wide (7–58 years). The vast majority of cases (86%–90%) involve the toes, with a curious predilection for the great toe accounting for 77%–80% of lesions (126–130). The distal phalanges of the fingers (thumb and index) are affected in 10%–14% of cases, with up to 75% of these lesions occurring in the dominant hand (131). Subungual exostoses are almost invariably solitary, with only rare reports of bilateral lesions.

At histologic analysis, subungual exostosis is readily distinguished from typical osteochondroma. Initially, the lesion is characterized by proliferating fibroblasts presumably induced by trauma. Cartilage metaplasia then develops within this fibrous background that later progresses to mature ossification (Fig 16). However, in contradistinction to osteochondroma, there is typically no continuity with the underlying cortex and medullary canal, and the cartilage cap consists of fibrocartilage rather than hyaline cartilage. These lesions may demonstrate an alarming growth rate, and findings from a small preexcisional biopsy may lead to concern for chondrosarcoma, as subungual exostosis is hypercellular and the cartilage cells may demonstrate plump nuclei. The lack of anaplasia and distinct radiographic appearance should lead to the correct diagnosis. Malignant degeneration has not been reported, to the best of our knowledge.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 16a.   Subungual exostosis of the great toe in a 21-year-old woman. (a) Clinical photograph shows skin ulceration related to the nail bed (arrow). (b) Foot radiographs reveal osseous protuberance from the dorsomedial aspect of the tip of the terminal tuft of the great toe (arrowheads) without definite continuity to underlying bone. (c) Photomicrograph (original magnification, x20; H-E stain) demonstrates the terminal tuft (*), the osseous excrescence (arrowheads) without cortical or marrow continuity, and the overlying fibrocartilaginous cap (open arrows). Focal regions of ulceration are also seen (solid arrows).

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 16b.   Subungual exostosis of the great toe in a 21-year-old woman. (a) Clinical photograph shows skin ulceration related to the nail bed (arrow). (b) Foot radiographs reveal osseous protuberance from the dorsomedial aspect of the tip of the terminal tuft of the great toe (arrowheads) without definite continuity to underlying bone. (c) Photomicrograph (original magnification, x20; H-E stain) demonstrates the terminal tuft (*), the osseous excrescence (arrowheads) without cortical or marrow continuity, and the overlying fibrocartilaginous cap (open arrows). Focal regions of ulceration are also seen (solid arrows).

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 16c.   Subungual exostosis of the great toe in a 21-year-old woman. (a) Clinical photograph shows skin ulceration related to the nail bed (arrow). (b) Foot radiographs reveal osseous protuberance from the dorsomedial aspect of the tip of the terminal tuft of the great toe (arrowheads) without definite continuity to underlying bone. (c) Photomicrograph (original magnification, x20; H-E stain) demonstrates the terminal tuft (*), the osseous excrescence (arrowheads) without cortical or marrow continuity, and the overlying fibrocartilaginous cap (open arrows). Focal regions of ulceration are also seen (solid arrows).

Treatment consists of complete surgical excision of the lesion. Attempts to surgically preserve the nail bed are often performed for cosmetic reasons. Allowing progressive lesion maturation may reduce local recurrence, although this treatment plan is controversial. The recurrence rate has varied between 11% and 53% (127).

Dysplasia Epiphysealis Hemimelica
Dysplasia epiphysealis hemimelica (DEH) is an uncommon skeletal developmental disorder representing an osteochondroma arising from an epiphysis. The reported incidence is 1 in 1,000,000 (132), and there is no definitive evidence that DEH is hereditary. Historically, DEH has been referred to by many names. It was originally described as "tarsomegalie" in 1926 by Mouchet and Belot (133). In 1950, Trevor used the name tarso-epiphysial aclasis, and this abnormality is also commonly referred to as Trevor disease (134). Subsequently, in 1956, Fairbank coined the current most frequently used term dysplasia epiphysealis hemimelica (135).

This disease predominantly affects the lower extremity (usually a single extremity), with upper extremity involvement only rarely reported in the humerus, ulna, and scapula (136). Interestingly, DEH is usually restricted to the medial or lateral side of the limb (hemimelic), with the former site affected twice as frequently as the latter (137). DEH is categorized into three different forms based on the disease extent and distribution: a localized form (monostotic involvement), a classic form (more than one area of osseous involvement in a single extremity), and a generalized or severe form (disease involving an entire single extremity). The localized form of DEH usually affects the bones of the hindfoot or ankle. The classic form shows characteristic hemimelic distribution and accounts for more than two-thirds of cases. It typically involves more than one epiphysis within a single lower extremity, particularly about the knee and ankle (talus, distal femoral, and distal tibial epiphyses) (Fig 17). In the generalized or severe form, there is involvement of the whole lower extremity. Pelvis involvement commonly affects the femoral head, symphysis pubis, or the triradiate cartilage, and hypertrophy of the ipsilateral iliac bone is frequently seen. These hip alterations may result in uncovering of the femoral head, simulating developmental dysplasia of the hip.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.   DEH involving the knee and ankle in a 6-year-old boy. (a, b) Lateral ankle (a) and anteroposterior knee (b) radiographs show lobular ossific masses protruding from the medial distal femoral epiphysis and talus (arrowheads). These findings represent epiphyseal osteochondromas. (c) Multiple coronal T1-weighted (600/20) MR images of the ankle reveal a large osteochondroma containing yellow marrow (*) and continuous with the cortex and marrow of the talus (arrows).

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.   DEH involving the knee and ankle in a 6-year-old boy. (a, b) Lateral ankle (a) and anteroposterior knee (b) radiographs show lobular ossific masses protruding from the medial distal femoral epiphysis and talus (arrowheads). These findings represent epiphyseal osteochondromas. (c) Multiple coronal T1-weighted (600/20) MR images of the ankle reveal a large osteochondroma containing yellow marrow (*) and continuous with the cortex and marrow of the talus (arrows).

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 17c.   DEH involving the knee and ankle in a 6-year-old boy. (a, b) Lateral ankle (a) and anteroposterior knee (b) radiographs show lobular ossific masses protruding from the medial distal femoral epiphysis and talus (arrowheads). These findings represent epiphyseal osteochondromas. (c) Multiple coronal T1-weighted (600/20) MR images of the ankle reveal a large osteochondroma containing yellow marrow (*) and continuous with the cortex and marrow of the talus (arrows).

At pathologic analysis, the lesion is a lobulated mass protruding from the epiphysis with a cartilaginous cap. The lesion is sometimes indistinguishable from the normal epiphysis. Its histologic features are identical to those of an osteochondroma, consisting of normal bone and hyaline cartilage with abundant enchondral ossification (135,141,142). The histologic findings support Trevor's hypothesis that the disease is a result of abnormal cellular activity at the cartilaginous ossification center (134). The normal cartilage sequence follows an orderly fashion of cell proliferation, maturation, senescence, and disintegration that does not occur in DEH. Trevor used the term aclasis in describing this failure of normal cellular breakdown (134).

Radiographic findings are often characteristic (Fig 17). In infants and toddlers, the affected ossification centers usually appear prematurely with eccentric, lobulated, overgrown, and asymmetric enlargement. Calcification, commonly stippled in appearance, is often seen throughout the anomalous cartilage. As the child grows older, the calcification becomes disorganized and is accompanied by irregular ossification (Fig 17). Subsequently, the ossifying epiphyseal osteochondroma becomes confluent with adjacent bone and eventually appears as a lobulated ossific mass, identical to any other exostosis, although marrow and cortical continuity with underlying bone may not be as apparent as in long bone lesions.

Premature closure of the physis may be present along with its consequence of limb deformity and limb length discrepancy. The articular surface is often irregular and, combined with the angular deformity, frequently results in premature secondary osteoarthritis. There may also be secondary involvement of the metaphysis resulting in undertubulation of bone.

CT is used to assess the continuity of the lobulated mass with the underlying epiphysis. It also demonstrates similar attenuation of tissue between the two structures, both composed of a combination of cartilage and osteoid. However, the relationship in planes other than axial is better evaluated with MR imaging.

MR imaging is extremely useful for identifying the extent of epiphyseal involvement, joint deformity, and effect on surrounding soft tissue, as with osteochondromas at other sites. Detail of the unossified cartilaginous mass and status of the articular and meniscal cartilage, and growth plate is optimally assessed with MR imaging (Fig 17c). The lesion and involved epiphyseal cartilage have similar signal intensity, with intermediate signal intensity on T1-weighted and high signal intensity on T2-weighted MR images (Fig 17c). Areas of low signal intensity on T1- and T2-weighted images indicate areas of calcification or ossification that increase as the lesion and patient's skeletal maturity progresses.

Biopsy is typically not necessary because of diagnostic radiologic features. However, a skeletal survey should be performed to exclude additional areas of involvement, particularly of the lower extremities. Surveillance and clinical assessment are usually continued until the patient reaches skeletal maturity. Surgical intervention is more frequently required for these lesions than for solitary osteochondromas because the epiphyseal location is often associated with pain, deformity, or loss of normal mechanical function (143,144). Excision, even incomplete resection, may result in a reduction of symptoms. Surgery is often more directed at improving joint congruity to lessen subsequent development of secondary osteoarthritis; thus, treatment at an early stage of disease improves outcome (134,143). Corrective osteotomies may also be needed to treat residual deformities.

Turret Exostosis and Other Osteochondromatous Lesions
A turret exostosis is an infrequent osseous excrescence originally described by Wissinger in 1966 as a smooth, dome-shaped, extracortical mass arising from the dorsum of a proximal or middle phalanx of the hand (145–147). Clinically, patients reveal an immobile, occasionally painful lump on the dorsum of the finger and usually recall antecedent trauma. The mechanism of injury is related to a deep laceration to the digital extensor mechanism resulting in the disruption of the periosteum and formation of a subperiosteal hematoma. As the hematoma matures, ossification occurs that often diminishes the excursion of the extensor tendon. This ossification leads to a progressive reduction in the ability to flex the finger.

Similar changes have been described at other ligamentous and tendinous attachments that we designate as "traction" exostoses. Additional osteochondroma-like lesions have been described in the hands and feet including bizarre parosteal osteochondromatous proliferation (BPOP or Nora lesion) and florid reactive periostitis (148–151). Both lesions are likely reactive, and a relationship to trauma has been suggested but not proved. BPOP usually affects the metacarpals and metatarsals (76%) and the hand (56%) more frequently than the foot (20%), although long bone (27%) and skull involvement have been reported (2,148–150). Florid reactive periostitis occurs in the hands and feet as well (2,151).

Depending on the time of imaging, the radiologic appearance is variable. Initially, radiographs may reveal only soft-tissue swelling at the affected site. As the injury heals, immature periostitis (laminated and more common with florid reactive periostitis) and the development of broad-based osseous excrescence (more often with turret or traction exostosis and BPOP) are seen on radiographs. The mature ossification with associated cartilage pathologically typically maintains a definable plane separable from the underlying cortex (Fig 18), although occasionally continuity is seen with traction exostoses. Bone scintigraphy shows varying activity with marked increased uptake initially that gradually decreases with maturation.

View larger version (96K): [in this window] [in a new window] [Download PPT slide]   Figure 18.   Turret exostosis of the finger in an 18-year-old man with history of previous trauma. Radiographs of the finger show a small ossific mass (arrowheads) adjacent to the terminal phalanx without definite cortical continuity to the underlying bone.

	Summary

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Pathologic Characteristics Solitary Osteochondroma Hereditary Multiple Exostoses Complications of Osteochondroma Cosmetic and Osseous Deformity Osteochondroma Treatment Osteochondroma Variants Summary References

 
In summary, osteochondroma represents the most common bone tumor, and the radiographic appearance of a lesion composed of bone demonstrating cortical and medullary continuity with the underlying parent bone is often pathognomonic. Osteochondromas that are sessile or involve complex areas of anatomy (spine or pelvis) are frequently better assessed with CT or MR imaging to detect the characteristic marrow and cortical continuity. Numerous complications are associated with osteochondromas including deformity (cosmetic and osseous), fracture, vascular compromise, neurologic sequelae, overlying bursae formation, and malignant transformation. These complications are more common in patients with multiple lesions (HME) as opposed to solitary osteochondromas. Imaging usually allows identification and differentiation of these causes of symptoms. Malignant transformation to chondrosarcoma occurs in approximately 1% of solitary lesions and 3%–5% of patients with HME. Development of chondrosarcoma is suggested when a cartilage cap more than 1.5 cm thick is found in a skeletally mature patient and is best evaluated with US and MR imaging. Variants of osteochondroma include subungual exostosis, DEH, turret exostosis, traction exostosis, BPOP, and florid reactive periostitis. The spectrum of radiologic features of osteochondroma, its variants, and complications are a direct reflection of its pathologic appearance. Recognition of these manifestations usually allows prospective diagnosis, helping guide therapy and improve clinical management of patients.

	Acknowledgments

 
The authors gratefully thank Teresa A. Choi and Cassandra "Kacy" Smith in the Department of Radiologic Pathology at the AFIP for preparation of the manuscript and figures. They also thank all past, present, and future attendees of the Radiologic Pathology Course at the AFIP for providing the material that makes such projects possible.

	Footnotes

 
² Current address: Department of Radiology, University of Wisconsin School of Medicine, Madison (J.J.C.).

Abbreviations: DEH = dysplasia epiphysealis hemimelica, H-E = hematoxylin-eosin, HME = hereditary multiple exostoses

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official nor as reflecting the views of the Departments of the Army, Navy, or Defense.

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