| Epidemiology | Osteochondromas are the most common benign bone tumors. They represent 35% of the benign and 8% of all bone tumours, although this is probably an underestimate since the majority are asymptomatic. Approximately 15% of patients with osteochondromas have multiple lesions (HME). |
| Clinics | The growth of the osteochondroma ceases at skeletal maturation or shortly thereafter. Patients may have a swelling of years duration causing symptoms related to the location and site of the lesion such as mechanical obstruction, nerve impingement, pseudoaneurysm of an overlying vessel, fracture at the stalk of the lesion, or the formation of a bursa over the osteochondroma. However most lesions are asymptomatic and found accidentially. The most serious complication is malignant transformation towards secondary peripheral chondrosarcoma, which is estimated to occur in <1% of solitary cases and 1-3% of hereditary cases. |
| Pathology | Pedunculated osteochondromas contain a stalk and are long and slender, while sessile ones are flat. Many exostoses are cauliflower shaped (figure). A fibrous perichondrium covers the cartilage cap and is continuous with the periosteum of the underlying bone. The cartilage cap is less than 2 cm thick and this decreases with age. A thick (greater than 2 cm) and irregular cap may indicate malignant transformation of the tumor. The cap covers the entire elevated surface of a sessile tumor, while it only covers the distal part of a pedunculated one. The cartilage cap merges into the underlying spongiosa. Here the chondrocytes are arranged according to an epiphyseal growth plate. A typical benign chondrocyte has a single small nucleus. During active bone growth, binucleated chondrocytes may be seen in benign tumors. The spongiosa of the stalk is continuous with the underlying cancellous bone. Fractures within the stalk may produce fibroblastic proliferation and even new bone formation. A bursa may develop over the osteochondroma and is usually attached to the perichondrium of the cap. The bursal wall is lined by synovium that may show inflammatory changes. |
| |  |
| |
| Figure 1: Histological appearance of a osteochondroma. A perichondrium (1) covers the cartilage cap (2). The cap merges into the underlying spongiosa, where the chondrocytes are arranged according to an epiphyseal growth plate (4). |
| |
| Treatment | The low rate of malignant transformation (<1%) is insufficient reason for resection. Osteochondromas are usually removed for cosmetic reasons, when symptoms of pain, limitation of motion, or impingement on adjecent structures such as nerves and blood vessels occur, or when roentogenographic features or an abnormal increase in tumor size suggest progression towards malignancy. When surgical resection is needed, the entire lesion should be removed, including the complete cartilaginous cap, to avoid recurrence. Multiple recurrence or recurrence in a well-excised lesion should raise suspicion of malignancy. |
| Evolution | Until recently, there has been a lot of debate about whether an osteochondroma is a developmental disorder or a true neoplasm. It was for long considered to be a perversion in the direction of bone growth. However, recent studies have shown osteochondroma to be a true neoplasm, since presence of loss of heterozygosity (LOH) and aneuploidy in osteochondromas indicate a clonal origin for the cartilaginous tissue of osteochondromas. Inactivation of both copies of an EXT gene in cartilaginous cells in the growth plate is required for the formation of osteochondromas in hereditary cases. |
| Prognosis | Complete excision of osteochondroma is usually curative. Failure to remove the entire cartilaginous cap or its overlying periosteum is the basis for most recurrences. Recurrence could also suggest malignancy. |
| Loss of chromosome band 8q24 in sporadic osteocartilaginous exostoses. |
| Mertens F, Rydholm A, Kreicbergs A, Willˆ©n H, Jonsson K, Heim S, Mitelman F, Mandahl N |
| Genes, chromosomes & cancer. 1994 ; 9 (1) : 8-12. |
| PMID 7507706 |
| |
| Chondrosarcoma (Primary, Secondary, Dedifferentiated, and Clear Cell). |
| K.. |
| |
| Osteochondroma (Osteocartilaginous Exostosis). |
| Unni KK |
| Dahlin's bone tumors. General aspects and data on 11,087 cases, Philadelphia Lippincot-Raven Publishers. 1996 ; 5 : 71-108. |
| |
| Clonal karyotypic abnormalities of the hereditary multiple exostoses chromosomal loci 8q24.1 (EXT1) and 11p11-12 (EXT2) in patients with sporadic and hereditary osteochondromas. |
| Bridge JA, Nelson M, Orndal C, Bhatia P, Neff JR |
| Cancer. 1998 ; 82 (9) : 1657-1663. |
| PMID 9576285 |
| |
| Clonal karyotypic abnormalities of the hereditary multiple exostoses chromosomal loci 8q24.1 (EXT1) and 11p11-12 (EXT2) in patients with sporadic and hereditary osteochondromas. |
| Bridge JA, Nelson M, Orndal C, Bhatia P, Neff JR |
| Cancer. 1998 ; 82 (9) : 1657-1663. |
| PMID 9576285 |
| |
| Up-regulation of PTHrP and Bcl-2 expression characterizes the progression of osteochondroma towards peripheral chondrosarcoma and is a late event in central chondrosarcoma. |
| Bovee JVMG, Van den Broek LJCM, CletonJansen AM, Hogendoorn PCW |
| Lab.Invest. |
| |
| Diminished levels of the putative tumor suppressor proteins EXT1 and EXT2 in exostosis chondrocytes. |
| Bernard MA, Hall CE, Hogue DA, Cole WG, Scott A, Snuggs MB, Clines GA, Lˆºdecke HJ, Lovett M, Van Winkle WB, Hecht JT |
| Cell motility and the cytoskeleton. 2001 ; 48 (2) : 149-162. |
| PMID 11169766 |
| |
| Cartilaginous tumors: fast contrast-enhanced MR imaging. |
| Geirnaerdt MJ, Hogendoorn PC, Bloem JL, Taminiau AH, van der Woude HJ |
| Radiology. 2000 ; 214 (2) : 539-546. |
| PMID 10671608 |
| |
| Heparan sulfate abnormalities in exostosis growth plates. |
| Hecht JT, Hall CR, Snuggs M, Hayes E, Haynes R, Cole WG |
| Bone. 2002 ; 31 (1) : 199-204. |
| PMID 12110435 |
| |