Question
In a 14-year-old boy who has had a
mushroom-shaped tumor in the distal femur for two years, which of the following characteristics suggests that the tumor has undergone
malignant transformation?
| A. |
Cartilage thickness > 3 cm
|
| B. |
Bone marrow is continuous with the parent bone
|
| C. |
The cartilaginous growth goes towards the joint
|
| D. |
Cartilage thickness > 2 cm
|
Show Answer
|
Correct Answer » D
Explanation
|
|
The image shows a pedunculated, mushroom-shaped bony outgrowth from the distal femur with continuity of cortex and medullary cavity with the parent bone. This is characteristic of osteochondroma, the most common benign bone tumor in adolescents.
Explanation of the Clinical Scenario:
- Osteochondroma is usually benign
- Malignant transformation (to chondrosarcoma) is rare but important
- The most reliable indicator is the thickness of the cartilage cap
- A cartilage cap thickness > 2 cm is considered suspicious for malignant transformation
- This is the most important and commonly tested criterion
Explanation of Other Options:
A. Cartilage cap thickness > 3 cm
Although clearly abnormal, the accepted exam cutoff is > 2 cm
B. Bone marrow is continuous with the parent bone
This is a hallmark feature of benign osteochondroma, not malignancy
C. Growth toward the joint
Osteochondromas typically grow away from the joint, but direction of growth is not a reliable indicator of malignancy
