Answer: Nonossifying fibroma (aka Fibroxanthoma, aka metaphyseal cortical defect)

and Yes, a NOF is a large (>3cm) fibrous cortical defect

NOFs are typically sharply demarcated, asymmetrical, cortically based lucencies with a thin sclerotic rim. They often appear multiloculated. They are located in the metaphysis, adjacent to the physis. As the patient ages they appear to migrate away from the growth plate.They have no associated periosteal reaction, cortical breach or associated soft tissue mass.

But did you notice both the lesion in the tibia as well as the distal femur? Anything come to mind? ie NF1, fibrous dysplasia and Jaffe-Campanacci Syndrome?