Written or medically reviewed by a board-certified physician. See About.com's Medical Review Policy.

Updated August 18, 2015.

The word "ectopic" is derived from the Greek word "ektopos" which literally means away from a place. You might have seen this word used in relation to an abnormal pregnancy, the ectopic pregnancy (where a fertilized egg implants outside the uterus in an abnormal location).  Similarly an ectopic kidney is a kidney in an abnormal location.  Typically the kidneys are present high up in the flanks towards the back, just underneath the diaphragm, protected by the lower part of  your rib cage.


When they are not present at this normal expected location, a diagnoses of renal ectopia, or ectopic kidney is made. It is a condition that is present by birth.

HOW COULD YOU END UP WITH AN ECTOPIC KIDNEY

It is easy to understand how an ectopic kidney might develop in the affected person if you realize that the kidneys do not develop at their usual location from the get go.  The kidneys in fact start off from embryonic structures in a developing fetus (from the Wolffian duct and the metanephric mesenchyme) deep down lower in the pelvis.  As the embryo develops, the kidneys change their relative position gradually and begin to rise up towards the chest.  Eventually they come to rest under the diaphragm.  However this journey from the pelvis to its usual normal location might be hampered because of multiple reasons.  These factors include genetic defects, and exposure to harmful chemicals during pregnancy (called teratogens- these include cigarette smoke, cocaine, mercury, pesticides, etc).

WHAT ARE THE CONSEQUENCES OF HAVING AN ECTOPIC KIDNEY 

Frequently, an ectopic kidney will be discovered only incidentally when an imaging study like ultrasound or an MRI is performed for other reasons.  The astute clinician might actually be able to palpate an abnormal mass which could lead to diagnosis as well.

The consequences of having an ectopic kidney can vary from no symptoms and no risk of kidney disease, to problems with drainage of urine from the kidney, to the worst case scenario where persistent partial blockage of urinary tract leads to kidney failure.  It is hard to predict who will develop these consequences and regular followup might be essential.

Problems with flow of urine could lead to repeated urinary tract infections, kidney stones, and a form of chronic kidney disease called reflux nephropathy. The abnormal location could also make the ectopic kidney more susceptible to trauma. Normal kidneys are deep-seated organs well protected by layers of muscle, fat, and the ribs. However an ectopic kidney might be more superficial. Blunt trauma received in contact sports for instance could hurt the kidney in this situation.

DIAGNOSIS OF ECTOPIC KIDNEY

As mentioned above, diagnosis could be incidental.  However if an ectopic kidney needs to be definitively diagnosed or if there is a family history, an ultrasound is a good initial test.  Relatively cheap and noninvasive, it should help delineate the location of the kidney as well as significant structural changes that might be present. If urine flow needs to be assessed, then invasive procedures like voiding cystoureterogram or an intravenous pyelogram will often be required. There is another test called a radionucleotide scan which can also confirm the kidney's location and possible blockage in the urinary tract.

HOW DO YOU TREAT ECTOPIC KIDNEY

The best possible scenario in a patient with an ectopic kidney is that it would be normal in function (which is entirely possible).  In this case no specific treatment would be needed except for regular monitoring for the expected complications done by a nephrologist.  Since one could be at a high risk of forming kidney stones or having kidney infections, dietary modification and adequate fluid intake might be all that is necessary.

Treatment will need to be escalated if there is a definitive proof of obstruction in which case reflux nephropathy can lead to future kidney failure.  Treatment of clinically significant reflux could require surgery or something called a sting procedure.