What does CT add?
In reality, in a lesion easily assessed on plain films, CT adds relatively little. In more difficult to image areas (e.g. pelvis / scapula / spine) it can shed light on the relationship of the mass to the underlying bone, showing continuity of the medullary cavity. It is also able to assess for aggressive bony features or a large soft tissue component, or the presence of a fracture.
How should one assess the cartilage cap?
MRI is the modality of choice to assess cartilage as well as the surrounding soft tissues.
A large bilobed exostosis arises from the posteromedial aspect of the distal femoral diaphysis, extending into the metaphyseal region. The medullary cavity of the exostosis is directly continuous with that of the femur and although the cortex is thinned in several areas, it remains intact.
The exostosis indents and distorts the semimembranosus posteriorly, the sartorius medially, and the vastus medialis anteriorly but there is no soft tissue mass associated with this lesion. No demonstrable cartilage cap. No pathological fracture or periosteal reaction demonstrated.