Bone
Osteosarcoma
Parosteal osteosarcoma

Author: Nat Pernick, M.D. (see Authors page)

Revised: 23 November 2016, last major update August 2013

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Parosteal osteosarcoma
Cite this page: Parosteal osteosarcoma. PathologyOutlines.com website. http://pathologyoutlines.com/topic/boneparostealosteo.html. Accessed December 9th, 2016.
Definition / General
  • Also called juxtacortical osteosarcoma (outside of the periosteum)
  • Ages 30 - 60 years, either no gender preference or female predominant
  • Arises in metaphyses of long bones
  • 70% occur at posterior aspect of distal femoral shaft, also tibia, humerus; rarely in hands, mandible
  • Slow growing; may not be detected for 15 years; symptoms of inability to flex the knee / painless swelling
  • Very good prognosis (80% 5 year survival); rarely recurs with dedifferentiation leading to worsening prognosis
Radiology Description
  • Prominent extracortical calcified mass that encircles bone
  • No continuity with bone or marrow
Radiology Images

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Mass behind knee

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Femur

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Distal femur xray - contributed by Dr. Mark R. Wick

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Proximal tibia xray - contributed by Dr. Mark R. Wick



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Bone surface mass

Case Reports
Gross Description
  • Large lobulated mass encircling bone, firm to hard
  • May contain cartilage
  • May have satellite nodules
Gross Images

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Cross section

Distal femur - contributed by Dr. Mark R. Wick

Contributed by Dr. Mark R. Wick



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Fleshy fibrous area with hemorrhagic dedifferentiated component

Micro Description
  • Low grade neoplasm of well formed bony trabeculae, osteoid, variable cartilage and highly fibrous spindle cell stroma in chaotic pattern
  • Stroma is hypocellular but malignant with mild atypia
  • 25% have medullary involvement
  • 15% have coexisting areas of dedifferentiation
  • Rarely has abundant osteoclast-like giant cells
  • No / rare mitotic figures
  • No fatty or hematopoietic marrow
Micro Images

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Ill-defined island of osteoid

Neoplastic bone

Grade 2

Contributed by Dr. Mark R. Wick



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Bland tumor cells producing trabeculae

Electron Microscopy Description
  • Numerous myofibroblasts, mixed with osteoblasts and fibroblasts
  • Normal cartilaginous areas
  • Undifferentiated cells have desmosomes between them (Hum Pathol 1980;11:373)
Differential Diagnosis