Small kidneys may be due to faulty development, as in hypoplasia and aplasia, or the cause may be atrophy secondary to disease in normally developed kidneys. In aplasia, specific renal structures are absent. In hypoplasia renal structures are found but in smaller numbers than usual. While aplasia is incompatible with life for more than a brief duration, hypoplasia may occur in different degrees of severity and thus support life for various periods of time.
Atrophy of the kidneys is most often due to pyelonephritis or glomerulonephritis. Frequently, atrophy occurs in hypoplastic kidneys, and it may be exceedingly difficult to decide which is the most important factor in ultimately determining the size of the kidneys.
The following case presents this problem along with some marked changes due to chronic renal insufficiency:
A 10-year-old boy was seen because of shortness of stature. He was 48 in. tall and weighed 51 lb. as