|The diagnosis of osteosarcoma is typically suspected by the radiographic appearance of the affected bone. It can present as a lytic or sclerotic lesion or as a mixed lytic-sclerotic lesion. Plain films reveal permeative destruction with poorly defined zones of transition with surrounding normal bone and lack of endosteal response. Ossification in the soft tissue in the radial or “sunburst” pattern is classic for osteosarcoma but is not a sensitive or specific feature. Periosteal new formation with lifting of the cortex leads to the appearance of a Codman’s triangle.|
The extent of the tumour in both bone and soft tissue is best appreciated with cross sectional imaging techniques such as computerized tomography (CT) or magnetic resonance imaging (MRI) (picture 2). This is particularly important prior to definitive surgery. Tumour extent, as defined by MRI, has been shown to be accurate predictor of tumour extent determined at the time of surgery. MRI has been accurate in accessing the intraosseous extent of the tumour and tumour extent with respect to muscle groups, subcutaneous fat, joints and major neurovascular structures.
A radionuclide bone scan, with methylene diphosphonate labelled technetium 99m defines the extent of the primary tumour and as its uptake will extend slightly beyond the limits of tumour, it helps to define a safe margin in surgical planning. It is also helpful in the detection of “skip lesions” within the same bone, as well as distant bone metastases (picture 3).
Because of the frequent presence of pulmonary metastasis at diagnosis (15-20%), CT of the chest is essential; these lesions often appear as calcified nodules.
Micrometastatic disease is present at diagnosis in 80-90% of patients but undetectable with any of present tests.
There are no known specific laboratory parameters. Increases of alkaline phosphatase or lactic dehydrogenase (LDH) serum level are observed in a considerable number of patients. Although they do not correlate reliably with disease extent, they may have negative prognostic significance.
The diagnosis of osteosarcoma must be verified histologically with a biopsy before initiation of treatment. In order to ensure appropriate biopsy techniques and an appropriate evaluation of the material, it is strongly recommended that biopsies should only be performed in specialized centres. A core needle biopsy under local or general anaesthesia is the most widely used technique. However open biopsy may be performed in order to obtain sufficient material for histological evaluation and ancillary studies.
MRI: left proximal humerus osteosarcoma
Bone Scan: left proximal humerus osteosarcoma