Low-grade intramedullary osteosarcoma

Introduction

• Usually affects young adults
• Mean age at diagnosis is 28 years
• Variable duration of symptoms prior to diagnosis
• Prognosis better than with conventional osteosarcoma
  
  
  

Location

Majority of tumors located in long bones, principally in metaphyseal region, less commonly in diaphysis

Plain films

Size

Usually large

Tumor effect on bone

Lytic lesion with internal trabeculations and variable degrees of internal sclerosis

Bone response to tumor

Generally poorly defined with  wide zone of transition; may demonstrate sharp, well-demarcated margins, however

Cortex

Lesions generally contained within bone without soft tissue extension or periosteal reaction

Pathology

• Microscopic: Lesions may be difficult to differentiate from fibrous dysplasia
• Well-formed trabeculae in variably cellular fibrous stroma
• Cytological atypia usually minimal
• Absence of osteoblasts and osteoclasts rimming trabeculae and infiltration between pre-existing bone trabeculae supports malignant diagnosis
  
  
  

Differential diagnosis

• Fibrous dysplasia
• Fibrosarcoma
• Infection
• Lymphoma
  
  
  

Complications

Pathologic fracture (rare)