Fibrosarcoma of the bone

Fibrosarcoma of the bone is a rare malignant bone tumor which may occur as a primary lesion, or secondarily after radiation treatment, dedifferentiation from other tumors ³ or pathologies such as Paget disease, bone infarction, or chronic osteomyelitis.

Terminology

It is a distinct entity from but similar to malignant fibrous histiocytoma ² (pleomorphic undifferentiated sarcoma) that may also rarely occur in bone, causing confusion in terminology, as the term "fibrosarcoma" has in the past encompassed a multitude of distinct histologic diseases. 

Epidemiology

Fibrosarcoma occurs primarily in 30-60-year-olds, with a slight male predominance. It constitutes <5% of primary bone tumors. Infantile fibrosarcoma is also rarely encountered in bone.

Pathology

Cells are fibroblastic in appearance with a somewhat uniform spindle shape. They may be arranged in fascicles creating a herringbone pattern. The degree of differentiation is variable, however, and therefore distinguishing features from other spindle cell neoplasm should be sought. Extracellular collagen fibrils are typical. 

Radiographic features

Plain radiograph

Typically highly destructive with a wide zone of transition, and occasionally expansile. Periosteal reaction is uncommon, but if seen is usually laminated, spiculated or Codman triangles. The lesion usually has no matrix mineralization, but may have areas of sequestered bone. These tumors are often associated with a large soft tissue mass extending from the bone ¹.

MRI

MRI is useful in defining intraosseous spread and the extent of extension into the soft tissues. Descriptions of the appearance of intraosseous fibrosarcoma on MR are few. 

Signal characteristics

The signal intensity pattern is nonspecific:

• T1: isointense to muscle
• T2: hyperintense to muscle
• T1C+: avid contrast enhancement (may be uniform or heterogeneous)