Why Does a Fetus Develop a Duplicate Kidney?

If there is premature branching or the occurrence of two ureteric buds on the same side during the embryonic period, it can lead to the formation of complete and incomplete renal duplication with duplicated ureters in the later stages of embryogenesis. Some patients have a family history, and the occurrence of renal duplication is associated with autosomal dominant inheritance. Renal duplication is a congenital developmental malformation also known as renal pelvis and ureter duplication malformation. In normal fetuses, the collecting system of the kidney may have mild separation. At the sixth week of human embryogenesis, the terminal end of the mesonephric duct opens into the cloaca and protrudes a small blind tube dorsally, known as the ureteric bud. The ureteric bud rapidly grows, and its apex is surrounded by primitive nephrogenic tissue, resembling a broad bean. The ureteric bud develops into the renal pelvis, with branches forming the renal calyces, and further branches forming the minor calyces and collecting ducts. Premature branching can lead to the formation of duplicated ureter malformations. The occurrence of renal duplication is associated with autosomal dominant inheritance. Mothers who are found to have fetuses with renal duplication should not panic as it is not a basis for termination of pregnancy. Simultaneous examination should be performed to check for the presence of other developmental abnormalities and malformations, especially the amount of amniotic fluid and fetal head development. If no other associated malformations are found, continuation of the pregnancy may be considered, and ultrasound examination is recommended 1-2 weeks later to monitor for any changes in renal hydronephrosis or amniotic fluid volume. Asymptomatic renal duplication without complications does not require treatment. However, if the upper pole of the kidney is infected, has hydronephrosis, stone formation, or ectopic ureter opening causing urinary incontinence, surgical resection of the upper pole kidney and ureter may be indicated. If the renal function of the duplicated kidney is good and there are no severe complications such as renal pelvis or ureter hydronephrosis, infection, or stones, ectopic opening of the duplicated ureter with bladder transplantation may be considered.