Benign processes such as a slow growing tumor will cause thick, wavy, uniform or dense periostitis. Since it is a low grade, chronic irritation, the periosteum has time to lay down thick new bone and remodel into a more normal appearing cortex.
Aggressive processes such as a malignant tumor cause a periosteal reaction that is more acute and high-grade. The periosteum does not have time to consolidate. It appears lamellated, “onion skinned”, amorphous or “sun-burst”.