Introduction
The development of the kidney is a circuitous process that begins during the sixth to eighth weeks of intrauterine life. During this process, the kidneys fail to ascend to their normal position leading to the condition called ectopic kidneys. It is a type of anatomical variation of the kidney which is usually asymptomatic. Most ectopic kidneys lie in the renal pelvis. In the majority of cases, ectopic kidneys usually do not cause any problems, and persons with this condition can live a normal life.
What Are Ectopic Kidneys?
Ectopic kidneys, also known as renal ectopia, can be defined as the abnormal positioning of the kidneys from their sublumbar location. This happens due to the failure of the kidney to ascend from its origin in the pelvis.
How are the Ectopic Kidneys Formed?
The urinary system develops from the intermediate mesenchyme, and kidney development takes place in three stages. Such as pronephros, metanephros, and mesonephros. The glomeruli develop in the metanephros stage; the ureteric bud arises from the mesonephric duct that divides in a branching fashion to form the renal pelvis, calyces, and collecting ducts. The maturation of the renal tissues takes place in the mesonephric stage. The fully formed kidney is initially located at the level of the sacral spine, which then ascends to the level of the upper lumbar vertebrae by rotating along its axis. The failure of the kidneys to ascend to their normal position results in abnormal positioning of the kidneys called ectopic kidneys.
What Are the Possible Sites Where Ectopic Kidneys Are Seen?
Around the eighth week of intrauterine life, the kidneys slowly move from the pelvis to their normal position in the lumbar region, but when ectopic kidneys occur, the possible sites where the ectopic kidneys could be seen include,
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It may stay in the pelvis near the bladder.
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It may stay in the lower abdomen.
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It may move too high up in the abdomen.
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It may cross the opposite side of the body and join with the other kidney, where two kidneys are located on the same side of the body. This condition is called crossed renal ectopia.
What Are the Types of Ectopic Kidneys?
The most common types include,
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Pelvic Kidney - When it is situated in the pelvis (fail to ascend).
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Thoracic Kidney - When it is situated in the thoracic cavity (ascends too high).
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Crossed Renal Ectopia - When it is situated on the opposite side (crosses to the other side).
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Crossed-Fused Ectopia - When it fuses with the other kidney on the opposite side.
What Are the Causes of Ectopic Kidneys?
The definitive etiology of ectopic kidneys is unknown; it is a birth defect that occurs during the developmental stage of the fetus. The suggested reasons include,
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An abysmally developed kidney bud.
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Due to any genetic defects.
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Lack of guidance for the kidney tissues to move to their normal position.
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Due to any drug or infection during the growth of the fetus.
What Is the Incidence of Ectopic Kidneys?
Most cases of ectopic kidneys are asymptomatic, so most of the time, it goes unnoticed. Hence the exact incidence of ectopic kidneys is unknown. The studies report that it occurs in 1 in 1000 live births.
What Are the Complications of Ectopic Kidneys?
Ectopic kidneys usually do not pose any problem as they are formed completely and function normally. But in some cases, it may cause complications such as,
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Vesicoureteral Reflux: It is a condition characterized by the backflow of urine from the bladder to the ureter or the kidneys, causing problems in the drainage of urine out from the kidneys.
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Urinary Tract Infections: Urinary tract infections may arise due to the obstruction or the blockage of urine as a result of vesicoureteral reflux arising secondary to the ectopic kidneys. This, in turn, causes the accumulation of bacteria in the kidneys, which are not flushed out properly, leading to infection in the urinary tract.
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Kidney Stone: Stagnation of urine in the kidneys or the bladder would result in the deposition of the calcium and oxalate crystals leading to the formation of kidney stones.
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Kidney Failure: In very rare cases, repeated renal stones and urinary tract infections may progress to kidney failure.
What Are the Symptoms of Ectopic Kidney?
Symptoms may occur as a result of complications of ectopic kidneys,
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Pain in the back of the abdomen.
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Pain or burning during urination.
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Hematuria (blood in the urine).
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Fever.
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Chills.
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High blood pressure.
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Presence of a lump in the abdomen.
How Are Ectopic Kidneys Diagnosed?
The majority of cases of ectopic kidneys are incidental findings as they appear to be asymptomatic in many people. The methods in diagnosis are as follows,
- Antenatal Assessment: The diagnosis of ectopic kidneys during pregnancy is possible in routine ultrasound scans. Studies report that 42 % of developing fetuses revealed an empty renal fossa in the case of ectopic kidneys. It may appear as small malrotated or fused (crossed ectopias) with numerous small blood vessels.
- Kidney Ultrasound: Ultrasound findings may reveal the location of the ectopic kidneys and the presence of renal stones.
- Voiding Cystourethrogram: It is a procedure to study the abnormalities in the bladder and the urethra and to find out the urethral reflex, which is the backward flow of urine into the ureters.
- Intravenous Pyelogram: It is a procedure in which a special die is injected into the kidneys to study the structure, size, and shape of the kidneys as well as the ureter and the bladder.
- Radionuclide Scan: A small amount of radioactive dye is injected into the kidney, and the scan is taken. This reveals the size and the location of the ectopic kidneys and finds out the presence of any blockages in the urinary tract.
- Computed Tomography (CT) Scan: CT scan is especially helpful in locating the ectopic kidneys located in the thoracic cavity.
- Magnetic Resonance Imaging (MRI): This also helps in locating the ectopic kidneys as well as giving details of their size, shape, function, and the presence of any blockages in the urinary tract.
- Urine and Blood Test: These tests may help in determining the state of kidney function.
How Are Ectopic Kidneys Managed?
Ectopic kidneys do not need any treatment as 90 % of cases are asymptomatic, and kidney functions are normal. Management is needed only when they pose a problem, such as a blockage in the urine flow or ureteral reflux. Surgery is indicated in such cases to remove the obstruction and to correct the backward flow of urine. Urinary tract infections should be treated with appropriate antibiotics. If the ectopic kidneys are not functioning properly, then they should be removed.
What Is the Prognosis of Ectopic Kidneys?
The prognosis of this condition is good as they do not cause any problems except for their abnormal position. Only 10 % of cases pose complications that can be corrected.
Conclusion
Ectopic kidneys are a rare congenital anomaly of the kidney. They are usually asymptomatic and are found incidentally. In some cases, it may produce complications obstructing the urine flow or ureteral reflux, which needs to be treated. It is important to know about this rare anomaly during surgeries involving the abdomen, pelvis, etc. Proper imaging studies should be done before finding out the presence of ectopic kidneys to prevent damage to the renal tissues.
