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.


  • Due to aberrant epiphyseal development
  • Most common benign bone tumor
  • 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

Reference: Stoller et al. Diagnostic Imaging: Orthopedics. 2004

Credit: Image Courtesy of