September 30, 2008


Fig. 1: Frontal radiograph of the right shoulder shows a broad-based exostosis with continuity of bone cortex and medullary marrow to the metaphysis of the humerus. 

Fig. 2: Axial T2-weighted MR image shows an exostosis with a bright cartilagenous cap (arrowheads), which is thin and smooth. 

This is a classic radiographic appearance of 'sessile osteochondroma' at the most common location (metaphysis) of bone. 

  • Most common benign bone tumor
  • Due to aberrant epiphyseal development 
  • Growth stops after skeletal maturation
  • Malignant transformation in 1-2% of solitary lesion 

  • Suspect malignant transformation if: growth after skeletal maturation, pain in the absence of fracture, bursitis or nerve compression
  • MRI  and CT to demonstrate thickness of cartilaginous cap, if >2 cm suspect malignancy
Stoller et al. Diagnostic Imaging: Orthopedics. 2004

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