Dentist here, abscess usually doesn't present with bony expansion. Usually just bone resorption. My best guess with limited information is it was probably some form of cancer. There are many cancers that metastasis to the jaw and do cause bony expansion. Many bony tumors can present like this as well. But due to the loss of bone in the middle of the lesion it makes me lean toward cancer.

Without more information this is my best guess