Osteosarcoma of femur - Radiograph and MRI

Radiograph of 20 year old female showing destructive lytic lesion involving the metaphysis of the medial aspect of femur with new bone formation and periosteal reaction (caudman triangle) {Arrow}

T1 weighted coronal image showing lytic destructive lesion with soft tissue, periosteal reaction and new bone formation.

Axial GRE image showing the new bone formation as hypointense signal and periosteal reaction as hyperintense signals.

Coronal STIR image showing the lesion.

Discussion: Osteosacroma is malignant tumor of bone in which neoplastic osteoid is produced by a proliferating spindle cell stroma.

• Most common primary malignant bone tumor of mesenchymal derivation.
• Arises in adolescents, and second or third decade.
• Affects males slightly more often than females. 

Affected sites:

• Occurs in region of knee (distal femur or proximal tibia) in 50% of patients. 
• Other sites include proximal humerus, proximal femur, & pelvis.
• Most osteosarcomas occur in the metaphysis.
• Infrequently occurs in the spine.

Classification:

1. Classic 
2. Telangiectatic 
3. Parosteal 
4. Periosteal

IMAGING:
Radiograph:

• Destructive lytic lesion or mixture of lytic and sclerotic areas (common).
• Moth eaten appearance with ill-defined zone of demarcation.
• Involves the metaphysis
• New bone formation.
• Periosteal reaction
• Visible soft-tissue mass.
• Spiculated / Sunburst appearance.
• 'Codman's Triangle' which is basically a subperiosteal lesion formed when the periosteum is raised due to the tumor.

CT Scan:

• Gives clearer indication of bone destruction.
• May depict small amounts of mineralized osseous matrix not seen on radiographs. 
• May be particularly helpful in visualizing flat bones, in which periosteal changes may be more difficult to appreciate.

MRI:

• Modality of choice in evaluating the local extent of disease because of its excellent bone marrow and soft tissue contrast and multiplanar capabilities.
• it assists in determining the most appropriate surgical management.
• Better delineates the involvement of the epiphysis, adjacent joint, adjacent soft tissues, neurovascular bundle, marrow extent and skip lesions.

Bone Scans:

• Increased uptake of radioisotope on bone scans obtained by use of technetium-99m (99m Tc) methylene diphosphonate (MDP).
• most useful in excluding multifocal disease but skip lesions are more reliable on MRI.