By definition, nodular keloids are those keloid lesions that have a round shape and are raised from the level of nearby skin. They measure 5 millimeters in diameter or more. Over time, nodular keloid lesions can grow in size. Once they reach a diameter of 20 millimeters, they are called tumoral keloids. These cut-off numbers, to call a keloid lesion nodule or tumor, are quite arbitrary and do not have any other significance.
We do not know why in some patients, keloid lesions develop and remain linear or flat, and in others, they develop and grow to become nodular, or tumoral. And of course, there are patients who have a mixture of keloid lesions, some nodular, some flat or linear.