On the enlargement of the normal congenitally solitary kidney

OBJECTIVE: To determine the anatomy of the normal congenitally solitary kidney and to complement an earlier investigation of the major functional parameters of congenitally and acquired normal solitary kidneys. MATERIALS AND METHODS: A healthy congenitally solitary kidney was compared anatomically with a normal control kidney from an equal pair in a man of similar height and age. RESULTS: The solitary kidney was about 1.8 times heavier than the control; the diameter of its glomeruli and convoluted tubules were similar to those of the control kidney but there were twice as many glomeruli in the solitary kidney than in the control. The total mass of glomeruli, as a percentage of the renal mass (about 5%), was the same for both kidneys and essentially similar to that for mammals in general. However, the total mass of glomeruli as a percentage of cortical mass was considerably greater in the congenitally solitary kidney than in the control, suggesting a relative deficit of convoluted tubular mass in the solitary kidney. CONCLUSION: The normal congenitally solitary kidney is hyperplastic, i.e. there are more elements (nephrons), and apparently not hypertrophic, i.e. having larger nephrons.