Atrophy of one kidney: The first one may be caused by narrowing of the artery supplying blood to the kidney, or it may be caused by chronic pyelonephritis, or it may be caused by trauma, or immune diseases such as aortitis, or congenital causes. The kidney itself is supplied by the renal artery. When a patient suffers from arteritis or arteriosclerosis, which leads to the narrowing of one side of the renal artery, it will cause one side of the kidney to be in a state of ischemia, which will cause one side of the kidney to atrophy after a long time. For kidney atrophy caused by this condition, a stent should be placed in the narrowed renal artery to improve the blood supply to the kidney. The second thing that can cause one side of the kidney to atrophy is chronic pyelonephritis. Chronic pyelonephritis is an infectious disease. Repeated infections in the kidneys can lead to unequal size of both kidneys, with one kidney shrinking more significantly. This cause of kidney atrophy can only be treated with anti-infection therapy to prevent further aggravation of the disease, but the atrophied kidney cannot be restored.