Thymus degeneration means that the thymus as an organ has atrophied or even died out, because this atrophy is a natural physiological phenomenon that occurs with age, hence the name degeneration. The thymus is a normal organ of the body, an immune organ, and an endocrine organ. During the embryonic and infantile periods, it has an important immune role, but as we grow older, the thymus reaches its peak size during puberty and then gradually shrinks and degenerates under the action of adrenal hormones and sex hormones, becoming smaller until it disappears completely and is replaced by fatty tissue and connective tissue. Therefore, the growth process of the thymus is an evolving one, and most adults have complete degeneration of the thymus that is not visible on CT or chest radiographs. However, there are some individuals who do not completely degenerate and thus can see the degenerating thymus on imaging.