Fibular Osteochondroma-MRI

Focal outgrowth in relation to medial side of fibular neck, with cortical and medullary continuity with fibular neck, with heterogenous appearance of the lesion. These findings likely suggest proximal fibular osteochondroma. Resultant  remodelling in posterolateral aspect of tibial metaphysis. Cartilage cap show variable thickness varying from 0.6cm to 1.3cm, with focal thickening of around 1.63cm in posteromedial aspect. Usually 1.5cm is considered thickeness of cartilage cap and needs clinical correlation and further evaluation for focal thickening of the cap. 

Learning Point: The cartilaginous cap deserves the most attention when differentiating a benign osteochondroma from a secondary chondrosarcoma that arose from a pre-existing osteochondroma In adults, the cartilaginous cap regresses and becomes thin due to enchondral ossificastion of the majority of the cap.
Malignant transformation is suggested by:

  • Cartilaginous cap thickness greater than 1.5cm
  • Cortical destruction
  • Backgrowth of the cartilaginous cap into the stalk or medullary canal
  • Lysis of calcifications in cap

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