Figure 7.1 Osteochondroma.

 

 

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. 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%.

General advice: Examiners may show an example of a solitary osteochondroma in an area that is difficult to access for the purposes of excision, but then insist that the patient wants it removed, e.g. posterior, proximal tibia. The resultant discussion is then used to assess knowledge of anatomy and approaches, e.g. posterior approach to the knee. If the MRI has shown no sinister features, and the lesion is asymptomatic, then you can have a reasoned discussion with the examiner about watchful waiting versus removal, i.e. both answers are perfectly acceptable.

Other points:

 

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Continued growth after physeal closure raises the suspicion of malignant transformation.

 

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EXT gene mutation is the genetic abnormality in multiple hereditary exostoses. It is an autosomal dominant condition.