Multiple hereditary osteochondromas (Diaphyseal achalasia).
Location
- Any bone with enchondral ossification can be involved
- Metaphysis of long bones: 70% , knee almost always involved.
Imaging Findings
Radiography
- Cartilage covered bony projection (exostosis) on external surface of bone.
- Calcification of hyaline cartilage cap.
- Pedunculated type: Slender pedicle directed away from joint.
- Lesion grows at right angles to long axis of host bone.
- Sessile type: Broad-based attachment to cortex
- Undertubulation of long bones (Erlenmeyer flask deformity)
- Malignant degeneration
- Development of thick, bulky, cartilaginous cap (thickness > 1 cm by CT, > 2 cm by MRI).
- Dispersed calcifications within cartilaginous cap.
- Development of soft tissue mass.
CT Findings
- To demonstrate continuity of cortical and medullary portions of lesion with host bone.
- To demonstrate thickness of cartilaginous cap.