Juxta-cortical chondrosarcoma

Juxta-cortical chondrosarcomas, also known as periosteal chondrosarcomas, are indistinguishable histologically from conventional medullary chondrosarcomas and are therefore graded into low, intermediate or high-grade tumors (see chondrosarcoma grading).

Epidemiology

Typically it occurs in adults in their 3^rd and 4^th decades and is slightly more frequent in males.

Pathology

Unlike conventional chondrosarcomas, they arise from the surface of the bone, lifting the periosteum over themselves as a fibrous pseudocapsule. The underlying cortex is usually thickened or may be eroded, however, extension into the medullary cavity is not usual. Where the periosteum is lifted a Codman triangle may be seen. In addition to the usual chondroid matrix, metaplastic ossification is also common.

Location

They typically arise from long bones, with a predilection for the posterior aspect of the distal femur.

Differential diagnosis

• periosteal osteosarcoma
  • affects younger patients (typically 10-25 years of age)
  • periosteal reaction perpendicular to the cortex
  • diaphyseal rather than metaphyseal
• parosteal osteosarcoma
  • stalk of bony attachment
  • otherwise similar appearance, location and demographics
• juxtacortical chondroma
• parosteal lipoma