The diagnosis of osteosarcoma is based on histologic confirmation of a clinical suspicion. For this to occur as expeditiously as possible, close collaboration between the specialists involved is necessary, particularly in the first instance, the clinician, often the orthopedic surgeon, the radiologist, and the anatomopathologist.
Clinical suspicion is derived from the proper consideration of such elements as the patient’s age, site of the lesion, and symptomatology.
Often diriment, for diagnostic purposes, is the radiological aspect.
Osteosarcoma, in fact can have a variable degree of ossification, and this characteristic directly affects the radiological appearance: the higher the level of ossification, the more radiopaque the appearance will be (“white” appearance on RX!!) and the easier the radiographic diagnosis will be.
The earliest radiologic aspects are represented by the presence of an irregular bony neoformation with radiolucent and/or radiopaque areas affecting the cortical over time.
As the tumor passes the cortical, it comes into contact with the periosteum, inducing what is called a “periosteal reaction”; the uplift of the periosteum by the tumor activates its bone deposition, which takes on extremely characteristic aspects with production of bony trabeculae, perpendicular to the bone surface, giving a radiological ‘sunburst’ appearance.
With time, the periosteal reaction itself, is eroded in the most central part by the tumor itself; the most peripheral part, which is still intact, takes on a triangular appearance that forms the radiological sign known as Codman’s triangle.
It should be emphasized that all of these features, which are often diagnostic, can be seen on a classic dual-projection, antero-posterior and latero-lateral radiograph.
Imaging is, therefore, usually completed with a Computed Tomography (CT) scan, both of the affected segment and of the lungs, and with a Nuclear Magnetic Resonance Imaging (MRI) of the limb, with and without contrast medium. The CT scan makes it possible to better highlight all those features present on radiography, such as the type of erosion, the presence of cortical erosion, the periosteal reaction, and to identify any distant metastases; the MRI of the affected segment, makes it possible to assess the intramedullary extension of the sarcoma, and the impairment of soft tissues, especially in the poorly osteogenic forms. Especially MRI, it is important to delineate the boundaries of the disease and identify the cutting margins to excise the tumor.
In the last decade, FDG-PET, a dynamic examination that allows the assessment of tumor metabolism based on the identification of cellular glucose, has taken on fundamental importance; the most aggressive cells, usually cancer cells, in fact consume more glucose, which is highlighted by the examination as it is labeled with a radioactive substance. PET scanning is then used both to search for possible metastases and to assess the tumor’s response to medical therapy.
Arteriography may still be of some use in rare selected cases.
Clinical-radiological suspicion, however clear, must be confirmed by biopsy sampling of pathological tissue and histological examination.
The biopsy is therefore necessary and although it “opens up” the tumor, it gives us information that is essential to be able to start treatment; it must be performed by experienced hands, usually by the same team that will then take charge of treating the tumor, because it must be performed at very specific sites, which can then be removed en bloc with the disease with surgery.