Congenital Anomalies of the Kidneys

Abstract

Congenital kidney anomalies are the result of embryonic maldevelopment that dates back to the fifth gestational week in humans. At this time-point, the metanephric mesenchyme, which originates from the nephrogenic cord, and the outgrowing ureteric bud, which originates from the nephric duct, display highly coordinated spatiotemporal interactions that result in the development of the kidney and the adjacent urinary tract (see Chap. 1, “Pre-natal Development of the Kidneys and Urinary Tract”). Disturbances in the molecular communication between the metanephric mesenchyme and the ureteric bud give rise to a spectrum of kidney abnormalities that differ from one another depending on the timing and/or location of the disturbance. Based on the location of the disturbance, congenital kidney anomalies can arise as unilateral or bilateral defects, or they can result in the formation of ectopic kidney tissue. Early perturbations lead to the complete absence of kidney tissue, whereas later events may result in an underdeveloped kidney that is hypoplastic or dysplastic or in a kidney with reduced nephron number. Many of these spatiotemporal disturbances are caused by genetic, epigenetic and/or environmental factors that are also involved in the development of other organs. Therefore, congenital kidney defects may present in conjunction with extrarenal defects or be part of a well-defined clinical syndrome. In this chapter, we discuss the phenotypic spectrum of human congenital kidney defects that encompasses unilateral renal agenesis (URA), bilateral renal agenesis, renal hypoplasia, renal dysplasia, multicystic dysplastic kidney (MCDK) as well as ectopic kidney tissue, kidney fusion defects (such as crossed fused ectopia and horseshoe kidney), and finally, duplication of the kidney. The clinical presentation, their management, and the syndromes that are associated with congenital kidney anomalies will be discussed. Finally, we provide a state-of-the-art overview of the molecular mechanisms that give rise to congenital kidney anomalies.