Dr. Kareem Maamoun | The renal system is the main regulator of fluid volume, concentration of electrolytes and pH level in the body. The kidneys begin to grow during the first month of the fetus’s life, and they may be subject to many problems during the development of the fetus. These problems can lead to complications after birth, but the right and early diagnosis may reduce the risk of these complications.

What are the most important fetuses’ congenital kidney disorders?

Kidney disorders that can occur during fetal development include congenital anatomical abnormalities and kidney dysplasia. Congenital malformations occur in the kidney more than any other organ in the body. Some of them are asymptomatic, do not cause any health problems and are only diagnosed incidentally, while others lead to serious disorders that may be life-threatening. The most important abnormalities include:

Renal agenesis: The bilateral development failure of the fetal kidneys leads to Potter syndrome, in which renal dysfunction is associated with structural deformities of the face and limbs. The affected children are born dead (stillborn infants) or die within a short period after birth.

The single kidney: In this case, one of the two kidneys is not created. One child out of every 500 children is born with a single kidney. This condition is diagnosed incidentally. Although it does not affect normal life, it is often associated with other abnormalities and an increased likelihood of sepsis and gallstones in the single kidney. This condition should therefore be monitored periodically.

Multiple kidneys: A third kidney may be found in very rare cases. The additional kidney is often atrophic and non-functional, and does not need any treatments unless it causes pathological disorders.

Renal hypoplasia: In this case, the kidney is small in size and lacking in function. It is usually asymptomatic so it does not need any intervention. However, if it causes frequent sepsis or pulmonary hypertension that cannot be treated with drug therapy, its eradication becomes indicated provided that the second kidney is normal. This is the case occur when a pregnant woman consumes alcohol or cocaine.

Horseshoe Kidney: In this case, there is a fusion between the lower poles of the kidneys. One child out of approximately every 1,000 children is born with Horseshoe Kidney. In most cases, the condition is asymptomatic, but it may sometimes cause a ureteric obstruction, along with the increased possibility of sepsis and renal calculi.

Ectopic kidney located in an abnormal position: The ectopic kidney is usually below its normal place, mostly in the pelvis, due to its failure to rise in the normal location during the fetal life. The ectopic kidneys are close to each other and may be attached to each other forming the shape of a doughnut, and in rare cases they may be located in one side.

Renal malrotation: The kidneys in the fetal life go up from the lower abdomen to the top with their rotation so that their navel will be inward. A renal malrotation may occur, making the navel outward. A Renal malrotation may occur outward instead of inward, making the navel of the kidney outward. An excessive renal rotation may occur, moving the navel backward.  The renal malrotation is usually accompanied by an ectopic kidney.

Ureteropelvic junction (UPJ) obstruction or narrowing: It is the most common cause of hydronephrosis for children, as this obstruction or narrowing leads to a rise in pressure inside the renal pelvis, causing an expansion of the pelvis and caliculi, and causing a gradual damage to the renal tissue. This condition is bilateral in 20% of cases, and may be diagnosed in the fetus during the pregnancy monitoring, or diagnosed in the baby when checking up the reason for the presence of palpable abdominal mass.

Complete or partial ureter duplication: This condition refers to the duplication of the pelvis and the ventral part of the ureter making two ureters come out of one kidney. Each of these two ureters can drain separately into the bladder, or they can be joined together to form one ureter draining into the bladder. This condition can be diagnosed in 1% of newborns. It is a healthy deformation that causes no symptoms and does not need any treatment.

Medullary sponge kidney: This type of disorder is characterized by the dilatation of the renal tubules, associated with an abnormal level of sepsis and renal stones.

Renal cysts and polycystic kidney disease: The polycystic kidney is the most common dysplasia affecting the kidney, and one of the two most common causes of kidney tumors in the fetus (along with hydronephrosis). In this case, the kidney consists of several cysts not connected to each other and filled with fluid, and the kidneys with renal cysts are not functional. However, this condition is actually unilateral, and most cases heal spontaneously.

As for polycystic kidney disease, it is a hereditary disease that has a recessive infantile pattern and a predominant adult pattern. In the infantile pattern, the condition is discovered during the evaluation of the palpable mass of the infant’s stomach, and the infected infant dies within weeks of birth. As for the adult pattern, it is discovered during adulthood, where the cysts are too large eventually developing into renal failure, with kidney transplantation being a good treatment option.

Hydronephrosis: This refers to the swelling of a kidney due to the obstruction caused by a build-up of urine, leading to its expansion and appearance in a larger size than normal. It is the most common cause of kidney tumors in the fetus. The UPJ obstruction or narrowing and the renal cysts are the most common causes of hydronephrosis. This disorder is divided to five degrees, with zero degree indicating the absence of hydronephrosis, and the fourth degree indicating the severe case. In case the fetus is diagnosed with hydronephrosis, the mother should refer back to the pediatric urologist between the periods of 20-30 weeks of pregnancy to monitor the condition of the fetus. It is possible that the condition disappears before birth or in the first few months after birth, so many first-, second- or third-degree cases do not require treatment, while in the fourth-degree case, surgery may be carried out to correct the defect, which is often enough to solve the problem.

How are fetuses’ kidney disorders diagnosed?

Most of the fetuses’ renal disorders are diagnosed incidentally before birth by radiography. Radiologists can radiograph the kidneys of the fetus in the 14th or 15th week of development. In the 20th week, the radiologist can see the internal structures of the kidney, and ultrasound waves help doctors diagnose malformations and renal dysplasia. Diagnosis of some conditions can also be delayed until after birth, where doctors resort to carry out an ultrasound or CT scan.

Do congenital kidney disorders need treatment?

Most renal anomalies are asymptomatic, accidentally diagnosed and do not need any treatment. Some cases may result in complications that necessitate drug therapy (sepsis, renal stones, pulmonary hypertension…), while some special cases require surgical treatment (severe hydronephrosis, renal hypoplasia, UPJ obstruction or narrowing, polycystic kidney disease).