ABSTRACT
Absence of renal tissue in the normal site, namely the renal fossa, may be due to true agenesis or to ectopic presentation of the kidney. The latter could be either in the fetal pelvis or due to a fusion with the contralateral kidney. In either case, the kidney could show signs of pelvicalyceal dilatation due to the abnormal position and contour of the drainage system. In true agenesis, the renal artery is absent on the ipsilateral side. Ectopic kidneys derive their blood supply from the aorta or the iliac arteries. Unilateral agenesis is usually an isolated finding, but may be part of the VACTERL association (vertebral, anal, cardiac, tracheo-(o)esophageal, (o)esophageal, renal, or limb abnormalities).
