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Ectopic Kidney

By Philip E. Gleason, MD

This topic section will provide introductory information on ectopic kidneys and renal agenesis. Often the kidneys and ureters develop together. While we discuss the kidneys in this section, you may also want to view the next topic section on ectopic ureters and ureteroceles as well.

Ectopic kidneys and renal agenesis cover a wide range of kidney findings and abnormalities. While the exact causes are not entirely known, these are all thought to result from abnormal kidney formation because of an abnormal ureteral bud. During in-utero development, the kidneys form when a ureteral bud comes off the bladder and stimulates, or induces, kidney tissue, known as the metanephric blastema, to begin developing into a kidney. As the kidney forms, it then begins to migrate and rotate along the retroperitoneum up to the normal kidney position along the upper back. If there is an abnormality of the ureteral bud or kidney blastema tissue, the kidney may not form or migrate correctly. This appears to occur to varying degrees in about 1 in 5,000 children. These can occur in both boys and girls.

• Sometimes the kidney will not form at all, and never develops, and is called renal agenesis.
  
  
• Sometimes the kidney tissue forms, but forms poorly and forms a scarred and poorly functioning kidney, known as renal dysplasia or as a multi-cystic dysplastic kidney (MCDK). Sometimes these kidneys will stay fairly big and can be fairly easily seen and followed. Other times they will shrink down and atrophy and involute and may more or less completely disappear.
  
  
• Sometimes the kidney tissue will form normally, but the kidney will be small in size, known as a hypoplastic kidney.
  
  
• Sometimes the kidney tissue will form normally, and the kidneys will be normal size, but the two kidneys may migrate abnormally or may be fused together known as ectopic kidneys or as a horseshoe kidney.
  

Often Ectopic Kidneys and Renal Agenesis cause no symptoms or problems. Remember, that while you normally have two kidneys, you can live a perfectly normal life with only one. As such they may not be diagnosed for years, and then sometimes only by accident or coincidence while doing x-rays or other testing. Often, when they are diagnosed, they will follow a benign natural course and will really not cause any specific problems.

On the other hand, because of the abnormal kidney development or position, they can sometimes be related to other problems such as vesico-ureteral reflux or blockage or obstruction of a kidney, etc. As such, they can sometimes be felt as an abnormal renal or abdominal mass or be found during x-ray evaluations of urinary tract infections or dilated, hydronephrotic kidneys, etc.

As a rule of thumb, ectopic or horseshoe kidneys without dilation, or hydronephrosis, may be a normal anatomic variant and may be more normal than abnormal.

On the other hand, if they are dilated and hydronephrotic, that may be a sign of related blockage or obstruction of a kidney. It may also be a sign of vesicoureteral reflux of urine going backwards from the bladder back up into the kidneys.

Of note is that while these abnormalities affect the ectopic or dysplastic kidney most directly, there can also be reflux or other findings in the more normal kidney as well. Thus, we do recommend that ectopic kidneys, horseshoe kidneys, dysplastic kidneys and renal agenesis be further evaluated with your physician or with a pediatric urologist. This will often including a VCUG bladder x-ray to look for vesicoureteral reflux and and possibly other further x-rays of the kidneys depending on the circumstances. This can be determined in evaluation of each individual patient in consultation with your physician.