Low grade central osteosarcoma

Low grade central osteosarcoma is an uncommon subtype of osteosarcoma accounting less than 1% of all osteosarcomas.

Epidemiology

Low grade osteosarcoma affects individuals of higher age group as compare to the other subtypes of osteosarcoma. The usual age of presentation is 19 to 54 years with the mean age of 33 years. It shows slight female predilection.

Pathology

Histologically it is a low grade tumour which occurs in the medullary canal of long bones. It contains osseous matrix with blend fibrous stroma and there is variable amount of bone production. Histologic pattern is similar to fibrous dysplasia and low grade parosteal osteosarcoma.

Location

Most commonly (85%) occurs in the metaphysis or diametaphysis of distal femur followed by proximal tibia. Less commonly (15%) it can be found in flat bones.

Radiographic features

Because fibrous dysplasia and central low-grade osteosarcoma are so similar histologically, the radiographic features are an extremely important part of the diagnosis. Radiographic features of low grade osteosarcomas are variable.

• most common pattern is as a large intracompartmental expansile lytic fibro-osseous lesion with coarsely thick or thin incomplete trabeculations
• another less common pattern is as a dense sclerotic lesion
• cortical erosion and soft tissue extension is also a common feature

Treatment and prognosis

In contrast to high-grade lesions, surgery will be sufficient in low-grade osteosarcomas. Although it is associated with a high incidence of local recurrence after inadequate surgical margins. Overall prognosis is excellent with survival rate ranges from 90 to 100%.

Differential diagnosis

Differential radiologic diagnoses include benign fibro-osseous lesions such as:

• fibrous dysplasia
• non-ossifying fibroma
• desmoplastic fibroma

Differential histologic diagnosis include:

• fibrous dysplasia
  • low-grade central osteosarcoma will contain some degree of cytologic atypia, whereas fibrous dyplasia does not
  • although the atypia is minimal, it is still an important distinguishing feature
  • the most helpful factor for differentiating low-grade central osteosarcoma from fibrous dysplasia is a permeative growth pattern
• low grade parosteal osteosarcoma