Osteochondromas: review of the clinical, radiological and pathological features.

Osteochondroma is the most common benign bone tumor and usually occurs in the metaphyseal region of the long bones. This tumor takes the form of a cartilage-capped bony outgrowth on the surface of the bone. The vast majority (85%) of osteochondromas present as solitary, nonhereditary lesions. Approximately 15% of osteochondromas occur as multiple lesions in the context of hereditary multiple osteochondromas (HMOs), a disorder that is inherited in an autosomal dominant manner. Most lesions appear in children and adolescents as painless, slow-growing masses. However, depending on the location of the osteochondroma, significant symptoms may occur as a result of complications such as fracture, bony deformity, mechanical joint problems and vascular or neurologic compromise. Malignant transformation of osteochondromas can occur later in adulthood but rarely metastasize. The treatment of choice for osteochondroma is surgical unless the skeleton is still immature. Pathogenetic analysis showed that HMOs are caused by mutations in either of two genes: exostosis (multiple)-1 (EXT1), which is located on chromosome 8q24.11-q24.13 or exostosis (multiple)-2 (EXT2), which is located on chromosome 11p11-12. Recently, biallelic inactivation of the EXT1 locus was described in nonhereditary osteochondromas. The EXT1 and EXT2 proteins function in the biosynthesis of heparin sulfate proteoglycans (HSPGs) which are multifunctional proteins involved in several growth signaling pathways in the normal epiphyseal growth plate. Reduced EXT1 or EXT2 expression in osteochondromas is associated with disordered cellular distribution of HSPGs, resulting in defective endochondral ossification which is likely to be involved in the formation of osteochondromas. Here the clinical, radiological, pathological and pathogenetic features and the treatment modalities of osteochondroma are reviewed.