A 16 year old boy was playing basketball. He planted, twisted, and fell to the ground in agony. Here’s his x-ray:
The finding is straightforward: fractured right femoral shaft. But if you look closely, you can notice that this is a ‘pathologic fracture’ with the presence of a bone cyst.
A pathologic fracture is one caused by disease that led to weakness of the bone (most commonly osteoporosis, but may also be due to cancer, infection, or a bone cyst).
Given his age and presentation, this is most likely an aneurysmal bone cyst (‘ABC’).
Although benign, ABCs can be locally aggressive and can cause generalized weakening of the bony structure. Usually patients will present with local pain that has been present for several weeks or months. They may even present with a pathologic fracture. Neurologic findings may develop (numbness, tingling, etc) secondary to pressure on nearby nerves. Definitive treatment is intralesional curettage but recurrence is not uncommon.
Here’s a more clear picture of an ABC from Radiopaedia:
