Unilateral Renal Agenesis in a 10 mm. Human Embryo

Abstract

On a priori grounds, failure of the kidney to develop has long been attributed'to absence of one of its 2 primordia—either the ureteric bud of the Wolffian duct or the metanephric blastema. Recently, in an instructive analysis of defective strains of mouse embryos descended from a pair of x-rayed ancestors, Brown has shown that mechanical conditions which delay or prevent the union of primordia, result in abortive kidneys or total absence of the organ. 1 It appears, however, from her published data, that in a number of cases absence of the organ might be attributed to total absence of a ureter, but there were no cases in which the blastema failed to appear.

This is in accord with the writer's earlier observations, 2 that when downgrowth of the Wolffian duct was interrupted, experimentally, in chick embryos, so that no ureteric bud was permitted to form, the blastema always appeared as a discrete mass of cells; which, however, failed to differentiate into tubules, in the absence of the ureter. Furthermore, from a re-study of these, and hitherto unpublished experiments with chick embryos, it seems that lesions sufficient to interrupt the downward growth of the Wolffian duct, to inhibit the formation of tubules in the lower part of the mesonephros and to injure the spinal cord, are not sufficient to prevent the appearance of the metanephric blastema.

In view of this difference in power of resistance exhibited by duct and blastema, the writer was not surprised when he found a 10 mm. human embryo in the Minnesota collection in which prospective absence of the left kidney could be explained on the basis of absence of the left ureter. In this specimen, which is being reconstructed for publication, the somewhat dilated left Wolffian duct terminated at the level of the pylorus.