Osteochondroma

Key Points:

  • Osteochondromas are the most common benign bone tumors and are comprised of a bony prominence with a cartilaginous cap
  • The presence of multiple lesions is associated with Multiple Hereditary Exostosis (MHE) and the EXT genes
  • Most commonly found in the metaphyses of long bones with a predilection for the distal femur and proximal tibia
  • The risk of malignant transformation to chondrosarcoma is approximately 1% for solitary lesions but can be up to 10% for MHE

Description:

Osteochondromas or cartilaginous exostoses are benign bone tumors comprised of a bony prominence with a cartilaginous cap (Geirnaerdt, 1993). Osteochondromas can occur as isolated lesions or less commonly patients have multiple lesions. The finding of multiple lesions is consistent with Multiple Hereditary Exostosis (MHE). The differential diagnosis includes Trevor Disease (dysplasia epiphysealis hemimelica), metachondromatosis, osteosarcoma, chondrosarcoma, chondroma, myositis ossificans and Ollier’s Disease (Tarassoli, 2009; Chin, 2000).

Epidemiology:

Osteochondromas are the most common benign tumor of bone accounting for 10% of primary skeletal tumors and 40% of benign bone tumors (Dahlin, 1986). The usual age of presentation is around 3 or 4 years, with rare presentation in infants.  Prevalence in the general population is reported at 1:50,000, however, actual prevalence may be higher than that due to asymptomatic disease (Tarassoli, 2009; Chin, 2000).  Both solitary osteochondromas and MHE affect males more commonly than females, 1.6-3.4:1 and 1.5:1 respectively. (Murphey 2000) Tumors are found most commonly in the metaphyses of long bones with a preference for those of the lower extremity, especially in the distal femur and proximal tibia (Murphey 2000).

Clinical Findings:

Most osteochondromas are asymptomatic, but 4% present with symptoms such as osseous deformity, growth abnormality, fractures or mass effect on surrounding structures. (Vanhegan, 2012) The tumors are frequently found due to cosmetic reasons, pain from friction or pressure on adjacent tissue or due to limited range of motion of the affected joint (Tarassoli, 2009; Biermann, 2002; Chin, 2000; Stieber; 2005).  Pseudoaneurysm, pseudoaneurysm rupture and hemothorax associated with local osteochondroma have been reported (Vanhegan, 2012; Patel, 2015). Short stature is associated with MHE, possibly due to a local effect of osteochondromas on the active growth plates of children (Staal, 2015; Solomon, 1951).

Imaging Studies:

Initial workup begins with history and physical examination including a detailed family history, especially in patients with two or more lesions. Radiographic imaging is the next step and can be diagnostic. Osteochondromas have a distinctive radiographic appearance (Murphey, 2000). The exostosis appears as a sharply demarcated bony lesion that contains both cortical and medullary bone, continuous with the parent bone; CT or MRI may be necessary to identify this continuity (Tarassoli, 2009; Biermann, 2002; Murphey, 2000). In MHE, the distal femurs develop an “Erlenmeyer flask” shapes, similar to Gaucher’s disease. CT and MRI are also useful to determine the extent of soft tissue impingement surrounding the lesion (Tarassoli, 2009). Ultrasound, CT and MRI can all be used to determine the cartilage cap thickness (Murphey, 2000). The cartilage cap thickness in children can be more than 2 cm but is concerning for malignancy in adults if it is greater than 1 cm (Biermann, 2002; Shtofmakher, 2015).

Etiology:

Osteochondromas have been historically viewed as developmental lesions, but there is evidence supporting a neoplastic origin (Biermann, 2002; Murphey, 2000; Porter, 1999). 
MHE is an autosomal dominant disorder with mutations in one of three different EXT genes (Tarassoli 2009). Approximately 80% of MHE patients have mutations in the EXT1 or EXT2 tumor suppressor genes which impact the migration and differentiation of chondrocytes (Tarassoli 2009).

Treatment:

Small or asymptomatic lesions are provided supportive care and observed (Murphey 2000). Surgical excision is the treatment of choice for a symptomatic osteochondroma. Indications include cosmetic concerns or symptoms such as limb length discrepancy and deformity, pain, bursa formation, instability, soft tissue impingement, spinal involvement, range of motion impairment, malignant transformation or vascular insufficiency (Tarassoli, 2009; Biermann, 2002; Chin, 2000). Complete excision of the cartilaginous cap is important to prevent recurrence (Murphey, 2000; Chin, 2000).  Surgical excision may be more useful for solitary lesions than for multifocal disease due to MHE. This may be due in part to complications with deformities of the parent bone (Murphey, 2000). Transformation to chondrosarcoma typically results in a low-grade malignancy that can be treated with wide resection (Murphey, 2000; Stieber, 2005).

Complications:

After surgical excision, the overall recurrence rate is estimated at 2% (Murphey, 2000). If patients present with new pain in an exostosis or growth of an exostosis during adulthood, it is advised they return to their physician for evaluation as these are indicators of malignancy (Biermann, 2002). Chondrosarcoma is the result of malignant transformation, which can occur in solitary lesions but is more of a concern in MHE with risks of 1% and up to 10%, respectively (Karasick 1997).  Malignant transformation has a greater tendency to occur in masses around the pelvis.  Surveillance of osteochondromas should be more frequent in adolescence as growth factors seem to contribute to tumor growth.

References:

  1. Biermann JS. Common benign lesions of bone in children and adolescents. J Pediatr Orthop. 2002;22(2):268-273.
  2. Chin KR, Kharrazi FD, Miller BS, Mankin HJ, Gebhardt MC. Osteochondromas of the distal aspect of the tibia or fibula. Natural history and treatment. J Bone Joint Surg Am. 2000;82(9):1269-1278.
  3. Dahlin DC, Unni KK, eds. Bone Tumors: General Aspects and Data on 8,542 Cases. 4th ed. Springfield, Ill., U.S.A: Thomas; 1986.
  4. Geirnaerdt MJ, Bloem JL, Eulderink F, Hogendoorn PC, Taminiau AH. Cartilaginous tumors: correlation of gadolinium-enhanced MR imaging and histopathologic findings. Radiology. 1993;186(3):813-817.
  5. Karasick D, Schweitzer ME, Eschelman DJ. Symptomatic osteochondromas: imaging features. AJR Am J Roentgenol. 1997;168(6):1507-1512.
  6. Murphey MD, Choi JJ, Kransdorf MJ, Flemming DJ, Gannon FH. Imaging of osteochondroma: variants and complications with radiologic-pathologic correlation. Radiogr Rev Publ Radiol Soc N Am Inc. 2000;20(5):1407-1434.
  7. Patel M, Bauer TW, Santoscoy T, Ilaslan H. Osteochondroma of the fifth rib resulting in recurrent hemothorax. Skeletal Radiol. 2015;44(12):1853-1856.
  8. Porter DE, Simpson AH. The neoplastic pathogenesis of solitary and multiple osteochondromas. J Pathol. 1999;188(2):119-125.
  9. Shtofmakher G, Kaufman MA, Bhoola PH, Patel AA, Rice SM, Cohen RE. Multiple osteocartilaginous exostoses of the lower extremity: a case report. Foot Edinb Scotl. 2015;25(1):62-65.
  10. Solomon L. Bone growth in diaphysial aclasis. J Bone Joint Surg Br. 1961;43-B:700-716.
  11. Staal HM, Goud AL, van der Woude H-J, et al. Skeletal maturity of children with multiple osteochondromas: is diminished stature due to a systemic influence? J Child Orthop. 2015; 9(5): 397-402.
  12. Stieber JR, Dormans JP. Manifestations of hereditary multiple exostoses. J Am Acad Orthop Surg. 2005;13(2):110-120.
  13. Tarassoli P, Amirfeyz R, Gargan M. Multiple hereditary exostoses. Orthop Trauma. 2009;23(6):456-459.

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