Sampling of suspicious bone lesions can be a nerve-wracking procedure. Several methods can be employed. All sampling methods require general anaesthesia and should be radiograph-guided. In each case, the centre of the lesion should be sampled as peripheral tissue is often simply reactive.
Samples for cytological evaluation need to be taken aggressively to achieve good exfoliation and a significant cell yield for interpretation. Even with good exfoliation, an accurate diagnosis is sometimes not possible, but cytology preparations can be useful for ruling out other conditions (eg osteomyelitis).
As a result, histological samples, typically Jamshidi needle biopsies, are commonly submitted. Owners should be warned that even these can be non-diagnostic. To increase the chance of getting a diagnosis, three good solid samples from the centre of the lesion should be submitted. The risk of pathological fracture using this technique is very low; however, should a fracture develop, it is likely to happen regardless of any intervention used. Ideally, the larger the sample the more likely it is to be representative of the underlying lesion, although the risk of pathological fracture is increased.
While this type of sample is less likely to be non-diagnostic, osteosarcomas can vary markedly in histological appearance in different regions of the same tumour and the subtype of osteosarcoma may not be truly represented in the sample submitted. For this reason, despite studies demonstrating an association between survival time and tumour grade, no histological grading system has gained widespread application. However, as a rule, central or medullary osteosarcomas tend to be high grade and those arising from bone surfaces are more likely to be low grade.
After excisional surgery, the entire tumour should be assessed for definitive diagnosis before considering chemotherapy. This may be submitted within an entire limb or a reduced sample including the tumour portion of the bone only. The submission must be fixed in an adequate volume of formalin for a minimum of 24 hours (some larger samples will require longer). Once they are fixed, samples may then be wrapped in wet tissue/swabs and double wrapped in thick plastic bags to prevent leakage. On receipt at the laboratory a representative biopsy will be prepared from the soft tissue if possible, to provide an interim report, but bone masses will require decalcification which takes up to 14 days depending on the sample size. Submission of a full clinical history and a radiographic image of the lesion are very useful in aiding interpretation of the histology.