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.