In many cases, a needle biopsy technique – either fine needle aspirate (FNA) or core needle biopsy (for example, a Tru-Cut core needle) – is the least traumatic approach. Both techniques may be used with or without radiographic visualization.
- Although FNA is done by surgeons, radiologists, and pathologists experienced in the technique, it is probably not appropriate for most centers. FNA generates a cytology specimen, unless small fragments of tissue are also obtained. We will use FNA for soft tissue extensions of bone tumors that are likely metastatic or hematological in origin.
- Core biopsy, on the other hand, often provides the pathologist with more tissue that may be more representative of the tumor. The additional benefit of a core biopsy is that tumor architecture is maintained, which is helpful when evaluating soft tissue tumors. We use Tru-Cut core needle biopsy for soft tissue sarcoma and for soft tissue masses arising from probable primary bone tumors.
Core biopsy of bone is useful for obtaining tissue from bony lesions arising in inaccessible regions such as the spine or the peri-acetabular pelvis. We generally perform these biopsies with the patient anaethetized using fluoroscopic control. Although core needle biopsy can be perform under local anaesthesia, the patient's discomfort may lead the surgeon to terminate the procedure before adequate material is obtained. This concern may not be as important when the cortex is eroded and easily perforated.
Open surgical biopsy is generally used in our center when it is necessary to obtain tissue from the intra-osseous compartment of the bone. We have not found needle biopsy of bone lesions lacking a soft tissue mass to be useful (except in the spine). If during the course of open biopsy an unexpected soft tissue mass is encountered, we generally limit the biopsy to the soft tissue mass as long as the frozen section confirms viable tumor in the soft tissues. Making a cortical window that exposes the patient to the risk of fracture is not undertaken unless necessary for diagnosis.
What Tests Should Be Done?
The surgeon should discuss the differential diagnosis of the lesion being biopsied with the pathologist to ensure that appropriate tests are undertaken. This is critical at the time of biopsy so that the tissue is fixed and processed in a fashion that permits these investigations. A frozen section is obtained before the procedure is completed. This frozen section is indicated primarily to ensure that a viable (not necrotic) specimen has been obtained. The frozen section also directs how the tissue should be processed.
For example, if the frozen section indicates the presence of a small cell tumor such as lymphoma or Ewing's sarcoma, a reasonable protocol would ensure that material is fixed in neutral buffered formalin, B-5 fixative (or another fixative which preserves nuclear detail in lymphoma cells), and glutaraldehyde (for electron microscopy). In addition to these fixed specimens, samples would be placed in culture medium for flow cytometry analysis and for cytogenetic studies.
Material should be immediately frozen at -70 degrees C to allow for later RNA and/or DNA extraction for identification of tranlocations specific for Ewing's sarcoma. The pathologist might overlook some aspects of this preparation of tissue unless guided by the differential diagnosis provided by the clinician and the histological appearance of the tumor at frozen section.
As a general rule, the surgeon should wait for the final diagnosis before proceeding to definitive treatment. However there are two situations in which the patient might benefit from undergoing biopsy and definitive management under one anesthetic, relying on the results of the frozen section to direct appropriate further surgical treatment:
- Aggressive bone tumors. In most cases of giant cell tumour, the lesion is peri-articular and the trauma of biopsy may predispose to an intra-articular fracture. It may be safer to proceed to definitive repair of the lesion following frozen section analysis if the pathologist is certain that the lesion is not malignant.
- Metastatic bone lesions. A patient presenting with bone disease likely arising from a known malignancy elsewhere may be at risk for fracture. Following confirmation of the metastatic diagnosis on frozen section, it may be prudent to proceed to immediate fixation of the bone involved by tumor.
To allow the surgeon to proceed with definitive surgery at the time of biopsy, the pathologist must be well versed in frozen section interpretation of bone pathology. The ready availability of a pathologist with expertise in musculoskeletal lesions is another reason why patients with aggressive and malignant primary bone tumors should be referred to a sub-specialty center prior to biopsy.
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