EXAMINER: So how would you obtain a tissue diagnosis?

CANDIDATE: A tissue sample can be obtained by biopsy. In general terms this can be performed by excisional, incisional or percutaneous means, but I would not perform a biopsy without first having discussed the case with a bone and soft tissue tumour MDT.

EXAMINER: Good. Let’s suppose you are the bone tumour surgeon now. When might you perform an excision biopsy?

CANDIDATE: The indications for an excision biopsy are narrow. The entire lesion is removed, and the margins are often marginal. Hence, this type of biopsy is really only applicable to benign lesions where the imaging has been diagnostic, for example lipomas, or where the lesion is small and superficial such that excision biopsy would not compromise later re-excision. However, if there is any doubt about the diagnosis I would perform a percutaneous or incisional biopsy first.

EXAMINER: OK, tell me how you would perform an incisional biopsy.

CANDIDATE: First, I would ensure I had appropriate imaging, ideally an MRI scan. I would perform the procedure through a short longitudinal incision. I would plan the incision using the imaging and position it such that the entire biopsy tract could be excised en bloc during the definitive resection, and such that it does not contaminate more than one compartment or key neurovascular structures. I would pay close attention to haemostasis and use minimal tissue dissection in order to minimize local tissue seeding.

EXAMINER: We perform most of our biopsies percutaneously now. Do you know any advantages or disadvantages to doing it this way?

CANDIDATE: I’ve seen biopsy performed by Tru-Cut needle. The procedure can be performed easily in clinic under local anaesthetic, which removes delay and the requirement for theatre time. Welker et al. have shown that it is safe, has a low complication rate and reliably provides enough tissue for diagnosis and treatment planning [1]. Other advantages are that it can be combined with imaging modalities, for example ultrasound for soft-tissue lesions and CT for bony lesions. The disadvantage is that necrosis and mitotic rate are less reliable on core needle, but this rarely affects management, and an incisional biopsy can always be performed subsequently if more information is required.

EXAMINER: What do you understand by a marginal margin?

CANDIDATE: A marginal margin, as described by Enneking, is when the resection line passes through the reactive zone of the tumour being excised [2].

EXAMINER: Explain to me what you mean by the reactive zone.

CANDIDATE: Tumours grow in a centifugal fashion and this leads to compression and subsequent atrophy of the surrounding tissue forming a pseudocapsule. Outside the pseudocapsule is an area of oedema where inflammatory cells and micronodules of tumour are present. This is the reactive zone. Hence, if a resection line passes through this reactive zone, as in a marginal margin, then micronodules of tumour are likely to be left behind, increasing the risk of a local recurrence.

EXAMINER: So, what other margins did Enneking describe and what do you understand by them?

CANDIDATE: Enneking described three other possible margins. He described intralesional margins, where the resection line passes through the tumour leaving macroscopic deposits of tumour in the surgical wound. He described wide margins, where the resection line passes outside the reactive zone and the tumour is excised with a surrounding cuff of normal tissue. In wide margins it is still possible that tumour will remain in the form of skip lesions. Finally, he described the radical margin, where the entire compartment in which the tumour resides is excised en bloc, in theory removing the entire tumour [2].

EXAMINER: So what stage is this tumour?

CANDIDATE: I would stage this tumour using the Musculoskeletal Tumour Society staging system as described by Enneking [3]. We’ve discussed that it’s a high-grade osteosarcoma, which makes it at least Stage II. It’s an intramedullary tumour that’s invaded the surrounding soft tissues making it extracompartmental and upstaging it to IIB. We’ve not discussed whether there is any evidence of metastasis yet, but, if there is, that would immediately make it a Stage III, regardless of the other features we’ve talked about.

COMMENT: This question will usually follow a discussion about a malignant tumour, for example osteosarcoma as in this example. The Enneking system is the easiest to remember and can be applied equally to bony and soft-tissue sarcomas. The other commonly used system is the American Joint Committee on Cancer (AJCC) system, which is more complicated. The AJCC also has separate systems for bony and soft-tissue tumours.

EXAMINER: This young lad has been referred to you urgently by his GP after his mum brought him in with a firm lump on the front of his left thigh. Tell me about his X-ray (Figure 24.1).

CANDIDATE: This is a lateral radiograph of his left femur including the knee joint but not the hip joint. There is a bony growth on the anterior aspect of the femur, which looks like a large osteochondroma.

EXAMINER: What makes you think it’s an osteochondroma?

CANDIDATE: Well, the cortices are in continuity with the bone as is the medullary cavity, and the lesion is extending out from the metaphyseal region of the distal femur, which is the most common site for these (25%). This is a sessile lesion rather than the pedunculated variety and appears to be a solitary lesion, although I’d want to examine the child to look for other lumps. It is quite a large lesion and there is some slightly atypical sclerosis within it, so I would definitely get an MRI scan.

EXAMINER: OK, so you get an MRI, which shows a nice thin cartilage cap and no worrying features. How are you going to treat it?

CANDIDATE: First I’d take a history and examine the child. I’d want to know if it is tender or symptomatic before I decide what to do.

EXAMINER: It’s not tender and it only bothers him occasionally if he knocks it, but his mother is adamant she wants it removed.

CANDIDATE: I would suggest a period of watchful waiting to see if it continues to grow or becomes more symptomatic. Removing it would carry risks of recurrence and neurovascular damage. There is also a chance of fracture during the operation and afterwards as it’s a large sessile lesion and removing it will weaken the anterior cortex of the femur considerably.

EXAMINER: His mum still wants it removed and she’s worried that it’s going to become cancer.

CANDIDATE: If this is a solitary lesion then malignant change is very rare indeed (< 1%). If the child has multiple hereditary exostoses the risk is a bit higher. The textbooks often quote figures of 10% but it is probably more like 1–5%.

EXAMINER: Tell me about these radiographs of this chap’s right foot (Figure 24.2).

CANDIDATE: Well they’re AP and oblique views and they show an expansile, lytic lesion in the proximal phalanx of his second toe.

EXAMINER: What do you think it is?

CANDIDATE: The radiographs show features consistent with an enchondroma. It has a short zone of transition and appears quite well defined. There’s also some stippled calcification within the substance of the lesion, which suggests a chondroid matrix.

EXAMINER: How would you treat this lesion?

CANDIDATE: Well I would want to get more information, so I would take a full history and examination. I would also want to get more imaging of the lesion with an MRI or CT and discuss the pictures with a bone tumour MDT. If there’s any doubt about the diagnosis they may want to do a biopsy, but in general the surgical treatment of an enchondroma is with curettage, with or without grafting.

COMMENT: Even if the diagnosis appears obvious and is of a benign lesion, don’t be rushed into offering surgical treatment. Always work through history, examination and imaging. You will never be criticized for discussing the diagnosis with a bone tumour MDT, but you will end up in a very tricky discussion with the examiners and fail if you have made the wrong diagnosis, it turns out to be malignant, and you’ve not discussed it with an MDT first.

EXAMINER: Tell me about this radiograph (Figure 24.3).