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Osteochondroma



General Considerations

  • Osteochondroma is the most common benign bone tumor and the most common skeletal neoplasm
    • They account for approximately 35% of all benign bone tumors and 9% of all bone tumors
  • They are cartilage-capped bony projections from the external surface of a bone
  • They occur only in bones which form by enchondral bone formation and most commonly found around the knee (40%) and shoulder, although they can occur in any bone
  • Almost all are diagnosed in patients under the age of 20 with a marked male:female predominance (3:1)
  • They grow until skeletal maturity and then stop growing when the epiphyseal plate fuses, although the cartilage cap can continue to grow slowly until about age 30
  • Osteochondromas tend to occur near an epiphyseal growth plate and grow away from the physis

Clinical Findings

  • Most are diagnosed incidentally
  • Or, they may come to clinical attention because they produce a mass
  • They are usually asymptomatic
  • When painful, they should be evaluated for
    • Mechanical irritation and inflammation of the surrounding soft tissues
    • Fracture of the stalk
    • Avascular necrosis of the cartilaginous cap
    • Malignant degeneration

Imaging Findings

  • Conventional radiography is the study of first choice
  • CT can be used to determine if the marrow and cortices of the lesion are continuous with the parent bone
  • MRI can be used to asses surrounding soft tissues and to measure the thickness of the cartilage cap, which can be important in evaluating for malignant generation
    • A thick cartilaginous cap (>1 cm) in adults should raise the possibility of malignant transformation
  • They can vary is size considerably, with the average tubular bone lesion being about 4 cm
  • Osteochondromas can either be sessile (flat) or pedunculated (stalk)
  • Sessile lesions are more likely to be associated with abnormalities of tubulation of the underlying bone leading to metaphyseal widening or a "trumpet shaped” deformity on x-ray

Malignant Degeneration

  • Fewer than 1% of solitary osteochondromas undergo malignant degeneration of the cartilage cap into secondary chondrosarcoma
  • It is usually preceded by
    • New onset of growth of the lesion
    • Rapid growth of a lesion, or
    • New onset of pain
  • The risk of malignant degeneration increases with an increase in the number and size of the osteochondromas
  • In general, a sessile lesion is more likely to degenerate into sarcoma than a pedunculated lesion (exostosis)

Associations and Syndromes

  • Hereditary multiple exostoses
    • Autosomal dominant condition
    • Short stature
    • Multiple osteochondromas
    • Asymmetric growth at the knees and ankles
    • Risk of malignant degeneration is 1-20%
  • Dysplasia epiphysealis hemimelica (DEH, Trevor disease)
    • Osteochondromas arising in the epiphyses
    • Involve the joint
    • Lesions restricted to one side of the body–either left or right
      • May be multiple lesions in a single limb
    • Primarily involves one side of an epiphysis
      • Medial side is affected twice as often as the lateral side
    • Usually occurs in infants or young children

Treatment

  • There is no treatment necessary for asymptomatic osteochondromas
  • The cornerstone of treatment is observation because most lesions are asymptomatic
  • If the lesion is causing pain or neurologic symptoms due to compression, it should be resected at the base
  • None of the cartilage cap or perichondrium should be left in the resection bed or  recurrence can occur.
    • As long as the entire cartilage cap is removed there should be no recurrence
  • Patients with many large osteochondromas should have regular radiographic screening exams for the early detection of malignant transformation

Osteochondroma. The white arrows point to a mushroom-shaped, pedunculated bony excrescence arising from the anteromedial aspect of the distal femoral metaphysis, attached to the parent bone and pointing away from the metaphysis.
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Henry DeGroot III, MD
eMedicine  Ian D Dickey, MD, FRCSC