High-grade surface osteosarcomas are sporadic and high-grade malignant osteoid-forming tumors emerging from the bony surfaces similar to parosteal and periosteal osteosarcomas.
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Epidemiology
High-grade surface osteosarcomas are very rare and constitute <1% of all osteosarcomas. There seems to be a peak incidence in the 2nd and 3rd decade of life and a male preference 1-5.
Diagnosis
The diagnosis of high-grade surface osteosarcomas is based on a combination of typical radiographic features with the histology of high-grade osteosarcoma.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 1:
imaging features of a bone tumor
histological finding of a high-grade osteosarcoma
origin from the surface of the bone
no significant intraosseous part
Clinical presentation
The most common complaints are swelling and pain 1. On rare occasions, there is joint stiffness or even no symptoms at all 3,4.
Pathology
High-grade surface osteosarcomas are highly malignant osteosarcomas growing from the fibrous periosteal surfaces and are one of the three subtypes of surface osteosarcoma together with parosteal osteosarcoma and periosteal osteosarcoma 1-3.
Location
The tumor has been found in the following locations 1-5:
Macroscopic appearance
Macroscopically high-grade surface osteosarcomas are of variable appearance mostly dependent on the type of generated extracellular matrix. The bulk of the tumor is usually located outside of the bone with infiltration and extension of the periosteum inwards and erosion of the underlying cortex 1.
Microscopic appearance
Microscopic features of high-grade surface osteosarcomas are those of conventional high-grade osteosarcoma 1.
Immunophenotype
Irrelevant for diagnosis 1.
Radiographic features
General imaging features of high-grade surface osteosarcomas are the following 1,2,5:
the tumor arises from the bony surfaces
dense ossifications
cortical erosions (≈50% of the cases)
medullary involvement (≈50% of the cases)
usually no cleavage plane between the main tumor and cortex
periosteal reaction uncommon
relatively high circumferential involvement (20-100%)
Plain radiograph
On plain radiographs high-grade surface osteosarcomas will usually display the following characteristics 1:
radiodense ill-defined
fluffy immature ossification
CT
CT can demonstrate the following:
osteoid matrix
cortical erosions
cortical thickening
medullary involvement
MRI
MRI can accurately depict soft tissue and medullary involvement of high-grade surface osteosarcomas as well as peritumoral and/or medullary edema.
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T1
osteoid matrix: low signal intensity
non-ossified soft tissue components: intermediate signal intensity
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T2
osteoid matrix: low signal intensity
non-ossified soft tissue components: high signal intensity
T1 C+ (Gd): marked enhancement
Radiology report
The radiological report should include a description of the following 1,6:
form, location and size
tumor margins and transition zone
circumferential extent
cortical erosion, cortical breakthrough
medullary components
soft tissue component
infiltration of neurovascular structures
Treatment and prognosis
Tumor management includes a combination of wide surgical excision and chemotherapy 2.
The five-year survival varies with different studies and ranges from roughly 40-80% 1-3. Localized disease and a good response to neoadjuvant good prognostic factors 1.
History and etymology
High-grade surface osteosarcoma was first described by the American orthopedic surgeon Kenneth C. Francis and his pathologist and surgeon colleagues Robert VP Hutter and Bradley L Coley in 1964 2,3,7.
Differential diagnosis
Conditions that can mimic the presentation of high-grade surface osteosarcomas include 1,4:
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usually aggressive periosteal reaction
less circumferential involvement
less medullary involvement
parosteal osteosarcoma: less circumferential involvement
osteosarcoma: the bulk of the tumor is located inside the bone