oncology
Osteochondroma (Osteocartilaginous Exostosis)
intermediate
6 min
28 marks
6 questions
Clinical Scenario
A 14-year-old boy presents with a painless hard lump on the inner side of his right knee that he first noticed 2 years ago. It has gradually increased in size but is not painful. On examination, there is a firm, non-tender, immobile bony prominence on the medial aspect of the distal femur. Range of motion is full. X-ray shows a bony outgrowth from the metaphysis with cortical and medullary continuity with the parent bone.
AP radiograph of the distal femur demonstrating a pedunculated osteochondroma arising from the metaphysis. The lesion shows continuity of the cortex and medullary cavity with the parent bone (pathognomonic). The stalk points away from the adjacent joint. A cartilage cap (not visible on X-ray) overlies the bony exostosis. This is a solitary lesion in a skeletally immature patient.
Source: PTPN11 Mutations in Metachondromatosis: Exostosis Imaging • PMC3077396 • CC-BY
Questions
Question 1 (4 marks)
Describe the clinical and radiographic features of osteochondroma.
Question 2 (5 marks)
What are the indications for treatment and surgical technique?
Question 3 (6 marks)
Describe hereditary multiple exostoses (HME).
Question 4 (5 marks)
How do you recognize malignant transformation?
Question 5 (4 marks)
What are the complications of osteochondroma?
Question 6 (4 marks)
Discuss outcomes and surveillance.
Exam Day Cheat Sheet
Must Mention
- •Most common benign bone tumor
- •Cortical + medullary continuity (pathognomonic)
- •Cartilage cap: <1cm benign, >2cm concerning
- •Growth stops at skeletal maturity
- •HME: EXT1/2, autosomal dominant, 1-5% transformation
- •Excise only if symptomatic
Common Pitfalls
- •Missing continuity criterion
- •Wrong cap thickness threshold
- •Wrong transformation risk
- •Operating unnecessarily
- •Missing HME genetics
- •Not knowing vascular complications