Osteochondroma
- most common bone tumor
- developmental lesion rather than a true neoplasm.
- 20%–50% of all benign bone tumors and 10%–15% of all bone tumors.
- composed of cortical and medullary bone with an overlying hyaline cartilage cap and must demonstrate continuity with the underlying parent bone cortex and medullary canal.
- Complications - deformity, fracture, neurovascular compromise, overlying bursa formation, and malignant transformation
- Malignant transformation is seen in 1% of solitary osteochondromas. Continued lesion growth and a hyaline cartilage cap greater than 1.5 cm in thickness, after skeletal maturity, suggest malignant transformation.
MRI of the osteochondroma (grey solid arrow) is the best radiologic modality for visualizing the effect of the lesion on surrounding structures and evaluating the hyaline cartilage cap.
High water content in nonmineralized portions of the cartilage cap shows intermediate to low signal intensity on T1-weighted images and very high signal intensity on T2-weighted MR images ( yellow pentagon).
MRI allows accurate measurement of the cartilage cap thickness and distinction from overlying muscle on MR images.
References:
Murphey MD et al :Imaging of Osteochondroma: Variants and Complications with Radiologic-Pathologic Correlation - Radiographics September 2000 20:5 1407-1434
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