41 Osteosarcoma

PART III Tumors

Osteosarcoma

George Nomikos, Anthony G. Ryan, Peter L. Munk, Mark Murphey

Clinical Presentation

A 14-year-old boy presented with an enlarging, painful, left distal femoral mass.

Figure 41A

Figure 41B

Figure 41C

Figure 41D

The radiograph shows a large destructive mass arising from the distal femoral metaphysis (Fig. 41A). Dense matrix mineralization is apparent in both the intraosseous and soft-tissue components of the lesion. The pattern of mineralization is cloudlike, compatible with osteoid mineralization. Also note the aggressive-appearing periosteal reaction and Codman’s triangle.

Sagittal T1-weighted images before (Fig. 41B) and after (Fig. 41C) intravenous contrast administration and a T2-weighted image (Fig. 41D) show a large area of marrow replacement in the distal femur and the associated soft-tissue component. In addition, there is a second, smaller focus of tumor in the femoral metaphysis separated from the primary tumor by normal intervening marrow.

Diagnosis

High-grade intramedullary (conventional) osteosarcoma with a skip metastasis.

Differential Diagnosis

None.

Discussion

Background

Osteosarcoma is the second most common malignant primary osseous neoplasm following myeloma. Although there are multiple subtypes of osteosarcoma, the conventional (or central intramedullary) type depicted in this case is the most common form. The most common skeletal location of the conventional osteosarcoma is about the knee, accounting for 50 to 55% of cases. Most affected patients are in their teens or twenties and there is a 2:1 male-to-female ratio. Lesions are most commonly metaphyseal, although diaphyseal (2 to 11%) and epiphyseal (< 1%) lesions may occur. Epiphyseal extension of metaphyseal lesions is common.

Pathology

Pathologically, these are malignant tumors of mesenchymal origin whose cells produce osteoid or immature bone. Some lesions contain areas of chondroid (5 to 25%) and fibroblastic-fibrohistiocytic differentiation (7 to 25%); however, most lesions are predominantly osteoblastic (50 to 80%).

Imaging Findings

RADIOGRAPHY

Although some lesions may be purely lytic or sclerotic, most usually demonstrate mixed lysis and sclerosis.
Abundant osteoid mineralization with a cloudlike appearance, cortical destruction, soft-tissue mass, and aggressive-appearing periosteal reaction (laminated, Codman’s triangle, or sunburst appearance) are common.
High-grade intramedullary tumors often disrupt the overlying cortical bone without causing osseous expansion, reflecting their aggressive behavior.
Lesions are often large at the time of presentation, and soft-tissue masses are commonly encountered.