Anatomical growth may be denoted to be the result of an interaction between hereditary and nonpathological environmental factors. In the general population, anatomical formations may be presumed to show a random size variation.
Pathological growth, in turn, may be denoted as the result of a disease entity interfering with the anatomical factors of growth. Pathological factors do not act alone in the determination of the final size. They must always combine with anatomical factors either to decrease or to increase anatomical size. This holds true even in agenesis actually caused by suppressing pathological factors.
Pathological influences will cause variations in size which may be expected to be distributed differently from the anatomical random variation. Pathologically caused size distributions may also differ, depending on the nature of the influencing pathology. Such differences may be due to many causes. For instance, the pathological influence may be exerted (a) in all individuals, or