Human embryo (12 mm) with mesohydronephrosis and ureterohydronephrosis.

This report describes a human embryo with a length of 12 mm (horizon XVII Streeterm 35 +/- 1 day old), in which the following malformations appear: Dilation on both sides of the Wolffian ducts, and the more caudal mesonephritic glomerules (mesohydronephrosis). Dilatation of both ureters and renal pelvis (uretero-hydronephrosis). These malformations are the result of the accumulation of liquid secreted by the mesonephros in a cloaca which is dilated, unwalled and blocked by an epithelial plug which is continuous with the cloacal membrane.