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Updated: Jun 21 2021

Parosteal Osteosarcoma

Images A - posterior femur - xray - Parsons_moved.png A - posterior femur - MRI- Parsons_moved.png B - post femur - xray Ap - Parsons_moved.png A_moved.png C_moved.jpg osteosarcoma histology.jpg
  • summary
    • Parosteal Osteosarcoma is a malignant, low-grade, osteosarcoma that occurs on the surface of the metaphysis of long bones. Patients typically present between ages 30 and 40 with a painfless mass.
    • Diagnosis is made radiographically with a heavily ossified, lobulated mass arising from the cortex with biopsy showing cellular atypia seen between regularly arranged osseous trabeculae.
    • Treatment is generally wide surgical resection. 
  • Epidemiology
    • Demographics
      • more common in females, age 30-40
    • Anatomic location
      • occurs on surface of metaphysis of long bones
      • most common sites include posterior distal femur, proximal tibia, and proximal humerus
        • 80% cases occur in the femur
      • marrow invasion occurs in 25% of cases
  • Symptoms
    • Presentation
      • often presents as a painless mass
      • limited joint motion can also be a presenting complaint for characteristic large posterior distal femoral lesions
  • Imaging
    • Radiographs
      • heavily ossified, lobulated mass arising from cortex
      • appears stuck onto cortex
    • CT chest
      • mandatory staging study
      • used to evaluate for pulmonary metastasis
    • MRI
      • mandatory and must include entire involved bone
      • helps determine soft tissue/marrow involvement and skip lesions
    • Bone scan
      • mandatory imaging study
      • always hot
  • Histology
    • Characteristic histology
      • low grade lesion
      • regularly arranged normal osseous trabeculae
      • most prominent histologic feature are the atypical spindle cells seen between regularly arranged osseous trabeculae
      • some cellular atypia should be seen to make diagnosis
    • Histology can be mistaken for fibrous dysplasia
    • High rate of MDM2 amplification and ring chromosome
  • Differential
    • Fibrous dysplasia
      • similar on histology, but xrays are different
    • Myositis Ossificans Traumatica 
    • Osteochondral exostosis (shares cortex with bone)
    • Developmental defect at insertion of adductor magnus
      • Differential of Parosteal Osteosarcoma
      • Bone surface lesion (cortex)
      • Similar Histology
      • Treated with surgery alone
      • Parosteal osteosarcoma
      • o
      • o
      • Periosteal osteosarcoma
      • o
      • Periosteal chondroma
      • o
      • o
      • Osteochondroma / MHE
      • o
      • o
      • Developmental defect
      • o
      • Myositis ossificans
      • o
      • Chondrosarcoma
      • o
      • Adamantinoma
      • o
      • Chordoma
      • o (controversial)
      • Fibrous Dysplasia
      • o
  • Treatment
    • Operative
      • wide local surgical excision
        • indications
          • standard of care in most patients
        • technique
          • many consider geometric osteotomy of involved bone to decrease long term morbidity and retain native joint
        • chemotherapy
          • chemotherapy not indicated unless there is a high grade component
        • outcomes
          • often curative
  • Prognosis
    • 95% long term survival when local control has been achieved
      • dedifferentiation of parosteal osteosarcoma is a poor prognostic factor
      • invasion into the medullary cavity does not affect long-term survival
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