Genitourinary Radiology > Embryology > Maturation of the Urinary Tract > Overview

Duplicated collecting system


  • Contact

    Maturation of the metanephric blastema and subsequent development of the excretory kidney is dependent on physical contact from the ureteric bud. The ureteric bud develops as an outgrowth of the mesonephric duct, and is located caudal to the developing metanephric blastema. The end of the growing ureteric bud enlarges as it approaches the metanephric blastema; upon physical contact between the ampulla of the ureteric bud and the metanephric blastema the metanephric blastema begins to develop (differentiate) and mature into renal tissue.

    1. Renal Agenesis
    2. Multicystic Dysplastic Kidney

  • Maturation of excretory and collecting systems

    When the ureteric bud contacts the metanephric blastema, it begins a process of division that continues for 12-14 generations. Metanephric blastema tissue surrounds, is carried by and grows with the dividing ureteric bud, developing into the excretory portion of the kidney that will eventually communicate with the collecting tubules formed by the ureteric bud. Each minor calyx with its associated collecting tubules and renal cortex constitutes one renal lobe. An average of 14 lobes are found in each kidney, which continue to mature until the age of 5 years. Persistent fetal lobation is seen in 5% of the population, which is a continuation of the lobar anatomy present at birth. In most cases, the lobar anatomy is obscured by the age of 4 to 5 years. Persistence is of no clinical significance but it could be mistaken for a mass unless the global pattern of fetal contour abnormality is recognized: renal parenchyma thickness should be normal (> 14mm) and the indentations should be smooth and regular and centered around a renal lobe. The calyces and medullary pyramid will be centered between indentations.

    1. Autosomal Dominant Polycystic Kidney Disease
    2. Medullary Sponge Kidney

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