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

Image Courtesy of