What is that area in the bone?

What is that area in the bone that is white, where the red arrow is pointing ?

This patient fell and has acute onset pain involving her ankle. She has a bone cyst also known as a aneurysmal bone cyst. She was most likely born with this cyst and never knew it until she had a trauma. We took an x-ray in the office which showed the cyst and then obtained an MRI scan. The arrow is actually pointing to where she broke through the bone where the cyst is located. This does not appear to be malignant. This will heal with immobilization in a cast boot.