October 12, 2010

Osteochondroma: Imaging Features of Malignant Degeneration

A radiograph of the right shoulder shows a large pedunculated lytic mass (long arrows) in the proximal metadiaphysis of the humerus, with continuous cortex and marrow cavity. Note areas of disrupted cortex (short arrows).

Facts: Osteochondroma
  • Benign bone tumor usually recognized on radiography as a lesion perpendicular to the parent bone, with a continuous cortex and marrow cavity.
  • Pain from an osteochondroma is commonly caused by fracture, burisitis or compression of surrounding structures. Malignant degeneration of a single osteochondroma is rare.
Facts: Malignant Transformation of Osteochondroma
  • 1% of solitary osteochondroma, 20% of hereditary form
  • If transformed, most are to chondrosarcoma
  • Average age of malignant transformation = 30 years
Imaging Features Suggesting Malignant Transformation
  • Clinical: 30 years old, location at pelvis and shoulder, increasing pain and mass at site of known osteochondroma
  • Imaging: thick/irregular calcified cap, bone destruction, soft tissue mass, altered appearance on sequential studies
Our case: pedunculated osteochondroma in a middle-aged patient presenting with increasing pain, suspicious for malignant transformation. Awaiting pathologic results.

1. Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 3rd ed. 2005
2. Tehranzadeh J. Musculoskeletal Imaging Cases, 2009

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