Low-grade central osteosarcomas (LGCOS) or well-differentiated intramedullary osteosarcomas are low-grade malignant bone-forming tumors typically arising within the intramedullary cavity of bone.
On this page:
Epidemiology
Low-grade central osteosarcomas are uncommon and account for 1-2% of all osteosarcomas 1-4. Most tumors are seen in young adults with a peak in the third decade of life 1-3. Women are slightly more commonly affected 1.
Diagnosis
The diagnosis of low-grade central osteosarcomas is based on a combination of typical radiographic features, location, histology and immunohistochemistry. Due to similar features to fibrous dysplasia, the diagnosis is often difficult, even in the setting of an experienced multidisciplinary meeting 2.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
imaging features of a bone tumor
location within the medullary cavity
fibroblastic bone-forming tumor with mild nuclear atypia and well-formed neoplastic trabeculae
MDM2 amplification is a desirable criterion.
Clinical presentation
Typical symptoms include swelling and/or pain 1 lasting from several weeks to several years at the time of presentation 1-4.
Pathology
Low-grade central osteosarcomas consist of fibroblastic tumor cells with mild nuclear atypia and well-formed neoplastic osseous trabeculae and originate from the medullary cavity 1,2.
Etiology
The etiology of low-grade central osteosarcomas is unknown 1.
Location
Low-grade central osteosarcomas are often found in the metaphyses or metadiaphysis of long bones 1 particularly the femur and tibia 1-3. They frequently extend to the end of bones 7. Rare locations are the jaws, small tubular bones of the hand and feet and the axial skeleton 6.
Macroscopic appearance
Grossly tumors are characterized by the following features 1-4:
fairly well-circumscribed margins
firm rubbery fibrous consistency
endosteal erosion of the cortex
Microscopic appearance
Microscopically, low-grade central osteosarcomas display the following histological features 1-4:
interlacing fascicles of spindle cells with mild to moderate cellularity
embedded in a fibrosclerotic background
mild nuclear atypia
woven or lamellar typically long and thick bony trabeculae usually in a parallel arrangement
possible presence of pagetoid bone
possible cartilage formation
focal lack of osseous matrix in some cases
In cases of differentiation, features resemble the histology of conventional osteosarcoma, undifferentiated pleomorphic sarcoma or fibrosarcoma and might lack osteoid formation 1.
Immunophenotype
On immunohistochemistry stains low-grade central osteosarcomas often express MDM2 and/or CDK4 as do high-grade sarcomas that result from their dedifferentiation 1, which can be used in the differentiation to its benign mimics 8.
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.
the most common pattern is as a large intracompartmental expansile lytic fibro-osseous lesion with coarsely thick or thin incomplete trabeculations 1,7
a less common pattern is a dense sclerotic lesion 7,9
cortical erosion/destruction and soft tissue extension are also common features 1,7
Radiology report
The radiological report should include a description of the following:
form, location and size
tumor margins and transition zone
periosteal reaction
cortical erosion, cortical breakthrough, soft tissue extension
bimorphic appearance
skip metastases
distant metastases
Treatment and prognosis
Treatment consist in wide resection and then low-grade central osteosarcoma has a good prognosis with overall 5-year and 10-year survival rates of >90% and >80% and a chance of metastases <5%. Recurrences happen after curettage and incomplete excision. Dedifferentiation carries a worse prognosis and such tumors are also treated with chemotherapy 1.
History and etymology
Low-grade central osteosarcomas were first described as ‘intraosseous well-differntiated osteosacroma’ in 1977 by the American pathologist Krishnan K Unni and his colleages David C Dahlin, Richard A McLeod and Douglas J Pritchard from the Mayo Clinic 11,12.
Differential diagnosis
Differential radiologic diagnoses include benign fibro-osseous lesions such as 4,8,13:
-
low-grade central osteosarcoma will contain some degree of cytologic atypia, whereas fibrous dysplasia 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
conventional osteosarcoma
Unable to process the form. Check for errors and try again.