Figure 1. An obvious reason for biopsy before surgery would be a case like this. Here a boy of 12 presented with pain in the left knee (a). The diagnosis was osteosarcoma, which meant the boy, would lose the distal half of his thigh bone (b) with a specialized joint replacement device (c). In this case I was able to save his tibia growing zone (d). He also required to undergo chemotherapy prior to surgery. All of these factors necessitate a biopsy to be done beforehand.

2. An excisional biopsy with minimal risk
In this procedure, the tumor is removed immediately without a biopsy. In principle this is done when removal poses minimal risk or morbidity to the outcome. Therefore if a patient presents with a small tumour (less than 3cm) it makes sense to just remove it immediately. It would be odd to biopsy it first because by the time a biopsy is done its already almost removed. Damage to surrounding tissue would also be minimal.

The same applies when the lesion is at the end of an expendable bone or structure like the rib, proximal fibula, distal ulna or distal phalanx. Especially in the proximal fibula a biopsy can result in leakage and contamination of the common peroneal nerve, which may have to be sacrificed thereafter (Figure 3).

Figure 3. This patient had a tumor in the proximal fibula (a). We approached the tumor laterally (b). Exposing the tumor showed the nerve in close proximity (arrowed, c). Obviously a biopsy here is ill-advised due to contamination of the nerve.

The spine is a special area for consideration. Often by doing a biopsy in the spine, it can become unstable and therefore one may be forced to do the biopsy and the main surgical procedure at the same time. For this reason a needle biopsy with a CT scan guide may be a better option but this can result in negative yield and therefore committing one to an open biopsy anyway.

It should be noted that an excisional biopsy is the most accurate modality of diagnosis compared to all other forms of biopsies.

3. An excisional biopsy with significant risk
These scenarios are the most difficult to manage. In such instances the biopsy itself may be a dangerous procedure and compel the excision of the tumor without a biopsy beforehand. Special categories of this include cartilaginous tumors, neural tumors and fat tumors. Careful understanding of the ramifications of the tumor needs to be understood.

Fatty tumors exist in three forms or grades namely, low, intermediate and high grade. The intermediate and high-grade tumors are usually sufficiently characteristic on MRI that a biopsy may be performed and a discussion of surgery and morbidity necessarily facilitated (as in 1 above). It may also qualify the need for preoperative adjuvant therapy (radiation and chemotherapy) if such is the practice. Low-grade tumors however look exactly like fat. They are very difficult to diagnose on biopsy due to sampling error – the tendency to biopsy a location in a tumor that looks benign. Because of this such a tumor may best be removed in toto as a malignant lesion (Figure 4) accepting the morbidity from loss of surrounding structures within reasonable limits (more or less muscle and minor nerves and vessels but perhaps not bone and major neurovascular structures).

 Figure 4. This tumor appeared to be fatty on MRI(a). It was seen to surround the sciatic nerve and femoral artery (circled). A biopsy was ill-advised as the tumor was close to these vital structures, had to be taken out anyway and if biopsied would have been subject to sampling error (b). In the specimen (b), we found three different tumor types from low-grade (well-differentiated) to intermediate grade. If the biopsy had sampled the low-grade area, the tumor would have been read as a benign tumor and either left alone or resected with less radical intent. Either approach could have been deleterious for the patient.

A similar problem is posed by cartilaginous tumors that again exist in low, intermediate and high-grade forms. The high-grade tumors are readily diagnosed but the intermediate and low-grade forms can be subject to sampling error and sometimes may look completely benign and later turn out to be malignant. The musculoskeletal oncologist must therefore be able to plan around the possibility that these low and intermediate tumors could be malignant even if seemingly benign. This usually takes the form of curettage with cryosurgery and a policy of close surveillance (Figure 5).

Figure 5. This boy had a fall and fracture of the left femur (a). We saw abnormal tissue at the fracture site and sent it for biopsy. This was read as a benign cartilaginous tumor (b). The fracture was stabilized and the patient followed closely. At 2 years he developed increasing pain (c). This was confirmed on CT scan to be a recurrence (d). The tumor was resected (e) and the limb salvaged with a massive prosthetic reconstruction (f).

Neural tumors inevitably result in nerve damage when subjected to biopsy or excision. This can result in paresis. Careful consideration is needed in this group of tumors (Figure 6). We have developed techniques of intraneural resection and repair of the nerve bearing the tumor that would minimize contamination and be compatible with limb salvage surgery (Figure 7). Typical tumors in this category are the nerve sheathe tumors (benign: Neurilemmoma or Schwannoma, malignant: Malignant Schwannoma), mixed nerve and sheathe tumors (neurofibroma and neurofibrosarcoma) and the PNET group of tumors (peripheral neuroepithelioma).