Bone & joints
Osteosarcoma
Parosteal osteosarcoma
Author: Nat Pernick, M.D.
Topic Completed: 1 August 2013
Minor changes: 18 October 2021
Copyright: 2003-2021, PathologyOutlines.com, Inc.
PubMed Search: Parosteal osteosarcoma
Table of Contents
Definition / general | Radiology description | Radiology images | Case reports | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Electron microscopy description | Differential diagnosisCite this page: Pernick N. Parosteal osteosarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneparostealosteo.html. 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
Mass behind knee
Femur
Contributed by Dr. Mark R. Wick
Distal femur Xray
Proximal tibia Xray
Case reports
- Patient with high grade intramedullary component (Hum Pathol 1989;20:488)
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
- Conventional osteosarcoma with periosteal spread
- High grade surface osteosarcomas: may be juxtacortical but different histology
- Myositis ossificans: orderly maturation, not attached to underlying bone; more active histologically
- Osteochondroma: tumor continuous with bone, fatty or hematopoietic marrow present
