Osteosarcoma


March 1, 2021 | By : OrthoFixar | Orthopedic Pathology
| Last updated on May 7, 2021


Osteosarcoma is a tumor characterized by the production of osteoid by malignant cells (Spindle cell).

  • It’s is the most common nonhematologic primary malignancy of bone.
  • Account for 20% of malignant bone tumor.
  • Occurs most commonly in the second decade of life.
  • The most important prognostic factor at the time of diagnosis is the tumor stage.
See Also: Differential Diagnosis for Bone Lesions

Types of Osteosarcoma

Primary Osteosarcoma

Primary Osteosarcoma includes:

  1. Intramedullary osteosarcoma.
  2. Parosteal osteosarcoma.
  3. Periosteal osteosarcoma.

Secondary Osteosarcoma

Secondary osteosarcomas occur at the site of another disease process. They rarely occur in young patients but constitute almost half of the osteosarcomas in patients older than age 50 years.

  • Osteosarcoma occurring with Paget disease.
  • Osteosarcoma after irradiation.

Telangiectatic Osteosarcoma

Telangiectatic osteosarcoma is a purely lytic lesion. On a radiograph, it can have an invasive appearance or it can have a ballooned appearance similar to that of an aneurysmal bone cyst.

Intramedullary Osteosarcoma

  • Intramedullary Osteosarcoma the most common type.
  • Usually occurs in children and young adults (mostly second decade of life).
  • Most common location is the distal femur and proximal tibia, it can also occurs in proximal humerus, proximal femur, and pelvis.
  • More than 90% of intramedullary osteosarcomas are high grade and penetrate the cortex early to form a soft tissue mass (stage IIB lesion).

Metastasis

  • 10% to 20% of affected patients have pulmonary metastases at presentation.
    • Lungs are the most common site for metastasis.
    • Bone is the second most common site.

Clinical Evaluation:

  • Pain, fever and swelling.
  • May feel a mass in the site of tumor.

Osteosarcoma Radiology:

  • A purely sclerotic or lytic lesion in which there is bone destruction and bone formation and a periosteal reaction (Codman’s triangle).
  • MRI is useful for defining the anatomy of the lesion with regard to intramedullary extension, involvement of neurovascular structures, and muscle invasion.
  • Bone scan: shows a hot spot.
    • Useful to evaluate extent of local disease and presence of bone metastases.
  • Chest CT is required to evaluate for pulmonary metastases.

Histology

  • Diagnosis depends on two histologic criteria:
    1. Tumor cells produce osteoid.
    2. Stromal cells are frankly malignant.
  • Tumor cells show significant atypia, and produce osteoid.
  • Giant cells may be present in giant cell rich osteosarcoma.

Differentials Diagnosis

  1. Ewing’s sarcoma.
  2. Leukemia
  3. Lymphoma
  4. Eosinophilic granuloma
  5. Osteomyelitis
  6. Desmoplastic fibroma
  7. Fibrosarcoma
  8. Dedifferentiated chondrosarcoma
  9. Secondary sarcoma
  10. Rhabdomyosarcoma

Treatment of Intramedullary Osteosarcoma

  • Preoperative chemotherapy for 8-12 weeks
  • Followed by wide-margin surgical resection (limb salvage).
  • Maintenance chemotherapy for 6-12 months after surgical resection.
  • Amputation indications:
    1. Pathologic fracture
    2. Encasing neurovascular bundle
    3. Enlarging during preop chemo AND adjacent to neurovascular bundle.

Parosteal Osteosarcoma

  • Parosteal osteosarcoma is a rare, low grade sarcoma.
  • It arises on the surface of the bone and invades the medullary cavity only at a late stage.
  • Women > Men
  • Mostly occurs at the age of 30-40 years old.
  • Most common sites are the posterior aspect of the distal femur, proximal tibia, and proximal humerus.
  • Patients often present with a painless mass.

Imaging Evaluation:

  • Characteristic radiographic appearance: a heavily ossified, often lobulated mass arising from the cortex (mostly the posterior aspect of the distal femur).
  • CT may be helpful in differentiating this subtype of osteosarcoma from myositis ossificans or an osteochondroma.
    • The ossification in myositis ossificans is more mature at the periphery of the lesion, whereas the center of a parosteal osteosarcoma is more heavily ossified.
  • MRI:
    • Helps determine soft tissue/marrow involvement and skip lesions.
  • Bone scan:
    • Shows a hot spot.

Histology

  • Parosteal Osteosarcoma histology is look like a low-grade intramedullary osteosarcoma.
  • It consists of slightly atypical spindle cells seen between regularly arranged osseous trabeculae.

Differentials Diagnosis

  • Fibrous dysplasia
  • Myositis Ossificans
  • Osteochondral exostosis
  • Developmental defect at insertion of adductor magnus

Treatment of Parosteal Osteosarcoma

  • Surgical resection with a wide margin.
  • Chemotherapy not required:
    • Except in high grade tumor.

Periosteal Osteosarcoma

  • Periosteal Osteosarcoma is a rare surface form (intermediate grade).
  • Mostly occurs in the diaphysis of long bones (typically femur or tibia).

Imaging Evaluation

  • It has a sunburst-type lesion rests on a saucerized cortical depression.
    • There is no involvement of the medullary canal.
  • Bone scan: Shows a hot spot.
  • CT scan: required for staging and evaluation the presence of pulmonary metastasis

Histology

  • Lobular and cartilaginous appearance.
  • Histology reveals areas of chondroblastic matrix although the tumor produces osteoid.
    • If histology shows no osteoid production, tumor would be classified as a chondrosarcoma.

Treatment of Periosteal Osteosarcoma

  • Preoperative chemotherapy for 8-12 weeks
  • Followed by wide-margin surgical resection (limb salvage).
  • Maintenance chemotherapy for 6-12 months after surgical resection.

High-grade surface osteosarcoma

  • High-grade surface osteosarcoma is extremely a rare form of surface osteosarcoma.
  • Imaging is a mixed lytic sclerotic aggressive surface lesion in the metaphysis or diaphysis.
  • Treatment is the same as conventional osteosarcoma.
  • Prognosis is the same as conventional osteosarcoma.

Telangiectatic osteosarcoma

  • Tissue of the lesion can be described as a bag of blood with few cellular elements.
  • Radiographic features of telangiectatic osteosarcoma are those of a destructive, lytic, expansile lesion.
  • Telangiectatic osteosarcomas occur in the same locations as aneurysmal bone cysts; radiographic appearances of both can be confused.

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