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380wing at the growth plate and are most frequently found The osteochondromas of HME differ from the patientswith solitary osteochondromas in that 90% of the lesions areof the sessile type19 (Fig. 5). Lesions in patients with HMEhave been described in almost every bone in the body exclud-

iatric Radiologist, Phoenix Childrens Hospital, Mesa, AZ.ress reprint requests to: Randy Ray Richardson, MD, Pediatric Radiolo-ariants of Exostosis of thendy Ray Richardson, MD

xostosis of the bone is a common finding in childrenpresenting with a mass in the extremity. The appearance

a solitary exostosis of the bone can be characteristic and thegnosis of an osteochondroma is often made without fur-r imaging. Multiple osteochondromas are seen in multiplereditary exostoses. Osteochondromas can be in specifications such as the epiphysis in Trevors disease. There areo several osteochondroma-like lesions that can occur asrmal variants or as the result of trauma, congenital anom-es, systemic disorders, or various causes of periosteal reac-n. In this article, we will review the imaging of the com-n osteochondroma and its associated diseases and thenus on a variety of causes of bony exostosis that can have ailar appearance.

steochondromaslitary osteochondromas are common lesions and may ac-nt for up to half of benign bone tumors.1,2 An osteochon-ma is an outgrowth of benign cartilage from the growthte that undergoes endochondral bone formation. The eti-gy of osteochondroma is not clear. Many believe an osteo-ondroma to be a true bone neoplasm. This may be sup-rted by the increased incidence of osteochondromas intients who have undergone radiation.3,4 Others have sug-ted that the outgrowth is a result of injury to the periph-l growth plate as suggested in animal models where thewth plate has been traumatized and a typical solitary os-chondroma is produced.5-7

Whatever the etiology (neoplastic or traumatic), patientsth solitary osteochondromas typically present with a non-der slow-growing mass. Occasionally, fractures of the pe-nculated osteochondroma can occur. Mass effect on adja-t structures such as bone (especially when they occur inforearm and leg), nerves, vessels, muscles, or even thenal cord can also be symptomatic1,8-10 (Fig. 1).ingkn

gist, Phoenix Childrens Hospital, 553 N. Orange Street, Mesa, Arizona85201. E-mail: randyjenny@hotmail.com

0037-198X/05/$-see front matter 2005 Elsevier Inc. All rights reserved.doi:10.1053/j.ro.2005.01.020one in Children

the metaphysis or metadiaphysis and tend to grow awaym the physis. The most common location for theseions is in the lower extremity. The femur is the mostmmon location followed by tibia and then humerus1,2

gs. 2 and 3).Radiographically these lesions appear either pedunculatedth a stalk or sessile with broad cortical attachment. There isaracteristic medullary and cortical continuity seen in bothes of lesions. The appearance of the cartilaginous cap isiable but can have rings of calcifications seen with otherondroid lesions. Radiographically, mineralization or ossi-ation of the cap can be seen with skeletal maturation (Fig.The thickness of the cap is typically measured byMRI andvary widely in thickness based on skeletal matura-

n.1,11-12

Excision of the osteochondroma is typically definitive, al-ugh recurrence has been reported in 2% of excised le-ns.13

ereditary Multipleostoses (HME)E is one of the most common skeletal dysplasias in chil-n and, as the name implies, is an inherited disorder trans-tted as an autosomal dominant trait. Males are affectedre frequently than females due to incomplete penetrancefemales.14-15 The overall incidence is approximately niner million.Patients with HME are typically identified during thet decade of life.16 Patients most commonly present withalpable mass or deformity from angulation of an ex-mity. Short stature is seen in 40% of patients, althoughst patients still fall within two standard deviations ofmean.17 The short stature is thought to result from

wing and angulation deformity as well as the develop-the calvarium. The most common location is about theee (distal femur and proximal tibia). In fact, it is so com-

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Variants of exostosis of the bone in children 381re 1 Osteochondroma of proximal tibia with mass affect on theula.re 2 Sessile osteochondroma of the distal femur.Figuchore 3 MR imaging of osteochondroma of the distal femur withss affect on muscle.re 4 Ossification of cartilaginous cap of a pedunculated osteo-ndroma of the proximal tibia.

Figu

Figure 6 Symmetric bilateral exostose

382 R.R. Richardsonn around the knee that another diagnosis should be con-ered if the bones about the knee are completely normal.1

her common locations include humerus, elbow, wrist, hip,kle, ribs, hands, feet, and scapula. Vertebral involvement ise but can occur and has been described arising from thesterior elements and from the vertebral body itself. Thetribution of lesions can be bilateral and almost perfectlymetric or unilateral and very asymmetric (Fig. 6). The

ference in distribution patterns may be attributed to dif-ent genetic types of HME.1,19

Radiographically the evaluation of the patient withHME cen-s on deformity and possible complications. Deformation isst commonly manifested as bowing of the bones. Coxa valgaeen in the proximal femurs, which can lead to uncovering offemoral heads.20 The forearm is frequently bowedwith ulnariation and shortening of the ulna (Fig. 7). Growth distur-nce of the distal radius and ulna can also result in a Made-g deformity of the wrist (Fig. 8). In addition to bowing ofleg, synostosis of the bones may occur when large osteo-

ondromas grow together. This is typically seen in the distalia and fibula but can occur in other parts of the body20

g. 9). Progressive erosion of an adjacent bone can be seenecially in the forearm and leg where long bones are juxta-sed11 (Fig. 10).mosidOtanrarpodissymdiffer

termois sthedevbalunthechtib(Fiesppo

re 5 Sessile osteochondroma of the proximal humerus.s in a patient with HME.

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Variants of exostosis of the bone in children 383Complications seen with both solitary osteochondro-s and HME include fracture, vascular injury, bursa for-tion, neurologic compromise, and malignant transfor-tion. The most worrisome of these complications islignant transformation. For solitary osteochondromas,lignant transformation occurs in less than 1% of cas-1,8 In HME, the frequency is higher. Studies have shownrevalence of malignancy ranging from 2 to 25%.1,8 Thest recent studies seem to favor a prevalence of around 35%.21-24 Radiographic manifestations include increasinge of an exostosis after puberty, lucencies or indistinct-ss developing within the exostosis, destruction of corti-bone, and soft-tissue mass. Cross-sectional imaging is

eful in the evaluation of the cartilaginous cap. Generally,artilaginous cap thicker than 1.5 to 2 cm in a skeletallyture patient should be considered worrisome for possi-malignant degeneration. In children, the cartilaginouscan be thicker, sometimes normally reaching a thick-

ss of up to 3 to 5 cm21-24 (Fig. 11).

revors Diseaseevors disease or dysplasia epiphysealis hemimelica isother process where exostosis of the bone is seen inildren. No inheritance pattern has been established. In

re 7 Shortening of the ulna with bowing of the forearm in aient with HME.evors disease, there is cartilaginous outgrowth typicallyolving tarsal bones or epiphyses of long bones. Histo- Figuically, the exostoses are identical to osteochondromasth a cap of hyaline cartilage and endochondral ossifica-n. The distal femur, distal tibia, and talus are mostquently involved. The process is typically unilateral;wever, there are several case reports of bilateral disease.ltiple bones of the same extremity are commonly in-lved and the lesions occur along the medial epiphysisre often than the lateral.25-27

Radiographically, small ossifications are seen along thedial or lateral aspect of a developing epiphysis or tarsalne. The small ossifications eventually become confluentth the epiphysis, forming an asymmetric mass. Deforma-n and angulation do not commonly occur; however, whensent, they can be severe and debilitating (Figs. 12 and 13).cause the lesions occur in the epiphysis, arthrography canused to define the extent of the lesion. Arthrography is alsoful to distinguish exostosis from loose bodies seen in sy-vial osteochondromatosis.28

osttraumatic Exostosischildren and adolescents partial or complete avulsionctures commonly occur due to the inherent weakness ofapophyses compared with the tendons. Avulsion inju-s at the musculotendinous junction continue to occurtil patients reach their mid-twenties (Fig. 14). The heal-process of such injuries may leave a prominent exos-is of the bone, which should not be mistaken for aneochondroma or any other neoplastic or infectious pro-s.28,29 Entities such as OsgoodSchlatter and Sindingrsen Johanssen, which have been mistakenly attributedre 8 Madelung deformity in a patient with HME.

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384 R.R. Richardsonosteonecrosis, now are considered to be part of thisectrum of partial avulsive injury to the apophysis.30 Theulting exostosis from a patient with chronic Osgoodhlatter disease can be dramatic (Fig. 15).

Figure 9 Synostosis of exostosere 10 A large osteochondroma of the proximal fibula causingsion of the lateral tibial metaphysis. FiguMyositis ossificans from trauma is a well-establishedse of soft-tissue calcifications. When the injury is deep,periosteum of the bone can be involved and ossifica-

n can attach to the bone. The result of this process canmistaken for an osteochondroma (Fig. 16). Synostosiseven be seen when myositis ossificans occurs between

nes that are closely apposed. This can look similar to

e distal fibula and tibia.re 11 MR imaging of a thick cartilaginous cap in an adolescent.

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Variants of exostosis of the bone in children 385tients with HME where two large osteochondromas fuseether.31

Subungual exostosis is an uncommon lesion that can ap-ar very similar to an osteochondroma. The exostosis occursnail bed of a digit of the hand or foot. The great toe is mostmonly affected. The lesion is thought to be due to trauma

th a reaction similar to myositis ossificans. Histologicallyy consist of trabecular bone with a cap of fibrocartilage.diographically they appear as a lobulated bony protuber-ce emanating from the nail bed.1

Turret exostosis is another type of posttraumatic exostosiscific to the proximal or middle phalanx of the hand. Ra-graphically the lesion appears to develop from disruption

re 12 Exostosis of the lateral epiphysis of the proximal tibia withociated valgus deformity in a patient with Trevors disease.the periosteum with formation of a subperiosteal hema-a. Radiographs demonstrate a broad-based bony exosto-

FiguOs, whichmay often be separated from the rest of the phalanxa lucent line32,33 (Fig. 17).Bizarre parosteal osteochondromatous proliferationOP) is a rare, benign lesion that was first described byra and coworkers in 1983 in the hands and feet of young

re 13 Postsurgical appearance of the same patient after resectionthe osteochondroma.re 14 MR imaging of the avulsive injury in a patient withgoodSchlatter disease.

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386 R.R. Richardsonults. The lesion is characterized by heterotopic bone risingm otherwise normal cortex, typically without evidence ofriosteal change or medullary contiguity (Fig. 18). BPOP islieved to be the result of minor blunt trauma to the affecteda.34

re 15 Chronic OsgoodSchlatter disease.copla

re 16 Myositis ossificans attached to the periosteum of the distala in a patient with healing fractures of the distal radius and ulna.ormal Variants andongenital Anomaliesistaken for Osteochondromase supracondylar process of the humerus may be easilystaken for an osteochondroma. It is simply an outgrowthbone that occurs along the anteromedial surface of thetal humerus and is typically oriented toward the joint,ereas pedunculated osteochondromas are oriented awaym the joint (Fig. 19). A persistent portion of the coraco-chialis muscle may insert on the process. It can also servean anomalous origin of the pronator teres muscle. Patientsth this anomaly may develop symptoms from compressionthe median nerve by the ligament of Struthers, whichginates from the supracondylar process and inserts to thedial epicondyle.35 Other similar bony processes occuroughout the body such as the os intermetatarsale, whichurs between the first and second metatarsals, and thechlear process of the calcaneus, which can be very prom-nt.Congenital anomalies can produce osteochondroma-e lesions. In patients with diastematomyelia a bone spurform within the central canal (Figs. 20 to 22). This can

differentiated from an osteochondroma by the presencea tethered cord with the cord split into two halves at theel of the bony spur. This is best depicted on MR imag-.Innumerable normal variations and normal appearancesbone exist in children that can have an appearanceilar to osteochondromas. The oblique view of the firsttatarsal in young children has a prominent exostosis-e process distally, which is normal (Fig. 23). Another

re 17 Turrets exostosis of the 1st proximal phalanx.mmon finding in children is spurring around the growthte that occurs with partial or incomplete closure along

theyseboa wmepo

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Variants of exostosis of the bone in children 387periphery of the physis. These epiphyseal and metaph-al spurs should not be mistaken for exostosis of thene or fractures36 (Fig. 24). Anomalies of the digits haveide variety of appearances with duplications, supernu-rary, and bifid digits as well as other various types oflydactyly36 (Fig. 25).

ystemic Disordersstemic disorders such as pseudohypoparathyroidism,eudopseudohypoparathyroidsim, tumoral calcinosis,d myositis ossificans progressiva can have osteochon-ma-like lesions and can be difficult to differentiatem hereditary multiple exostoses. In particular, myositis

Figureationgraphswellimonthof myaxial Cshownbasedtent wificans progressiva, a rare progressive familial disease,have an appearance strikingly similar to HME because

naPathe diffuse ossification of ligamentous insertions result-in metaphyseal exostoses. Fortunately, these systemicorders with soft-tissue ossification and osteochondro--like lesions often have characteristic findings of thends and other laboratory data to differentiate them fromE.37

eriosteal Reactionere are many causes of periosteal reaction that can causene formation and exostosis that can appear similar to os-chondromas. Potential etiologies include a parosteal os-sarcoma, osteoid osteoma, and osteomyelitis. Parostealeosarcoma with its typical sessile attachment to the exter-

arre parosteal osteochondromatous prolifer-). (Reprinted with permission34). (A) Radio-merus after shows no fracture. Soft-tissueeen in lateral aspect of upper arm. (B) Six, radiograph of humerus shows developmentossificans. (C) Twelve months after injury,ws peripherally calcified soft-tissue mass (notsistent with myositis ossificans. Corticallyis seen without medullary contiguity, consis-OP.ofingdismahaHM

PThboteoteoost

18 Biz(BPOPof hu

ng is ss laterositisT sho) conlesionith BPl cortex can radiographically mimic an osteochondroma.tients with a parosteal osteosarcoma (Fig. 26) are usually

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388 R.R. Richardsoner and present with a painful mass. Also, in contrast toeochondromas, parosteal osteosarcomas arise from thetex of the bone and do not commonly involve the medul-y cavity.38 Even so, definitive differentiation is usually a

re 19 Supracondylar process of the humerus.re 20 Saggital CT of a central bony spur in a patient with di-ematomyelia. Figubination of imaging and clinical and histological evalua-n.39

In summary, exostosis of the bone is a common finding inildren. Despite the many normal variants, posttraumaticions, systemic disorders, and various causes of periostealction that can mimic osteochondromas, the diagnosis of aitary osteochondroma and HME is often established with-t advanced imaging because of their characteristic conven-nal radiographic appearance.

re 21 Axial CT of a central bony spur in a patient with diastem-myelia.re 22 MR imaging of a diastematomyelia.

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Figure 25 Bifid distal phalanx.

Variants of exostosis of the bone in children 389re 23 Oblique view of the foot shows a prominent exostosis-likecess distally in the first metatarsal.re 24 Normal variant epiphyseal spurs of the distal radius in anlescent. Figure 26 Parosteal osteosarcoma of the distal femur.

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section. Orthopedics 14:809-812, 19918. Mirra JM: Benign cartilaginous exostoses: osteochondroma and osteo-

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Variants of Exostosis of the Bone in ChildrenOsteochondromasHereditary Multiple Exostoses (HME)Trevors DiseasePosttraumatic ExostosisNormal Variants and Congenital Anomalies Mistaken for OsteochondromasSystemic DisordersPeriosteal ReactionReferences