Bone & joints


Parosteal osteosarcoma

Topic Completed: 1 August 2013

Minor changes: 18 October 2021

Copyright: 2003-2021,, Inc.

PubMed Search: Parosteal osteosarcoma

Nat Pernick, M.D.
Page views in 2020: 4,304
Page views in 2021 to date: 3,959
Cite this page: Pernick N. Parosteal osteosarcoma. website. Accessed October 20th, 2021.
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

AFIP images
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Mass behind knee

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Contributed by Dr. Mark R. Wick
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Distal femur Xray

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Proximal tibia Xray

Case reports
Gross description
  • Large lobulated mass encircling bone, firm to hard
  • May contain cartilage
  • May have satellite nodules
Gross images

AFIP images

Cross section

Contributed by Dr. Mark R. Wick

Distal femur

Microscopic (histologic) 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
Microscopic (histologic) images

AFIP images

Ill defined island of osteoid

Neoplastic bone

Grade 2

Contributed by Dr. Mark R. Wick
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
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