Supernumerary Kidney - Symptoms, Diagnosis, and Treatment

What Is a Supernumerary Kidney?

As the name suggests, a supernumerary kidney is the presence of more than two kidneys in the urinary system. It is a rare condition, and only 80 to 100 cases have been reported in the medical literature. The problem arises when individuals are born with an additional kidney. This condition is known as a supernumerary kidney. The extra kidney might be the same size or larger than a normal kidney. It is either firmly or loosely attached to the normal kidney or in some other location in the urinary system. The treatment of a supernumerary kidney depends upon the problems associated with it.

How Is a Supernumerary Kidney Formed?

A supernumerary kidney can be present anywhere in the urinary system. It can be present below, above, behind, or in front of the normal kidneys. It has been found that the supernumerary kidneys are most commonly present on the left side of the abdomen and below the normal kidneys. In order to learn about the formation of a supernumerary kidney, it is important to understand the formation of normal kidneys. The mechanism of formation of a supernumerary kidney has been described below:

• The formation of the kidneys begins in the embryo in the third week of pregnancy. A structure known as the urogenital ridge forms three kidneys: the pronephros, mesonephros, and metanephros.

• Out of these three kidneys, only the mesonephros and metanephros form the definitive human kidneys.

• A structure known as the ureteric bud originates from the mesonephros to initiate the formation of kidneys.

• However, the problem arises due to the premature division of the ureteric buds or when two or more ureteric buds come out of the metanephros.

• As a result, the urinary tract shows the formation of an additional kidney known as the supernumerary kidney.

What Are the Symptoms of a Supernumerary Kidney?

Normally, the patient does not present with any symptoms in the case of a supernumerary kidney. However, the following symptoms are noticed when other kidney disorders accompany the supernumerary kidneys:

1. Fever.

2. Hypertension, or high blood pressure.

3. Presence of a lump or a mass in the abdomen.

4. Abdominal discomfort and pain.

5. Urinary incontinence or the leakage of urine might occur in some situations.

What Methods Are Used to Diagnose Supernumerary Kidneys?

Supernumerary kidneys are often confused with duplex kidneys, but there is a vast difference between the two. Duplex kidneys, also known as duplicated ureters, are a congenital condition characterized by the presence of two drainage systems for the kidneys. On the contrary, supernumerary kidneys have their separate blood supply, drainage system, and renal capsule (a thin membrane covering the kidneys' outer surface). The following tests are recommended to diagnose supernumerary kidneys:

• Physical Examination - The doctor checks the physical signs of a supernumerary kidney. A mass or a lump can be felt in the abdominal region on palpation. Along with a physical examination, the patient's blood pressure is also measured. It is because hypertension or high blood pressure is one of the symptoms of supernumerary kidneys.

• Laboratory Tests -

  • Blood Test - The doctor might ask the patient to undergo a blood test to check the body's general health and the presence of infections. The blood reports are normal in patients having a supernumerary kidney.

  • Urine Test - In this test, the patient needs to collect the urine in a container or a sterile bag provided by the hospital. The urine sample is then examined in a laboratory to check the presence of blood, bacteria, stones, and other anomalies. The urine test reports are usually normal in patients having an extra kidney.

• Imaging Tests - The following imaging tests are used to diagnose supernumerary kidneys:

  • Intravenous Pyelography - Intravenous pyelography is one of the imaging tests that help to detect the problems of the kidneys, ureters, and urinary bladder. In the case of supernumerary kidneys, the X-ray images obtained after the procedure show the presence of additional kidneys with a drainage system.

  • Computerized Tomography (CT) Scans - It is most commonly used to diagnose supernumerary kidneys because it provides three-dimensional (3D) images of the organs. As a result, an extra kidney can be seen on the X-rays.

Does the Patient Need to Undergo Any Treatment for a Supernumerary Kidney?

The patient does not present with any symptoms unless other disorders like hydronephrosis, vaginal atresia, and pyelonephritis are associated with a supernumerary kidney. Asymptomatic patients are usually kept on follow-ups, and imaging tests are done repeatedly to check the condition of the kidneys. A nephrectomy is usually indicated if the kidney is non-functional and causing trouble to the patient. Before undergoing nephrectomy, the patient needs to undergo an imaging test, known as the renal angiogram, which has been described below:

• Renal Angiogram - It is an imaging test that helps look at the kidneys' blood vessels. As the supernumerary kidney has a separate blood supply from the normal kidney, a renal angiogram is done before nephrectomy to locate the blood vessels and save them from getting damaged. The doctor injects contrast material into the artery that supplies blood to the kidneys. X-rays are then obtained from different angulations to determine dye flow into the blood vessels. After the renal angiogram procedure is complete, the patient is ready for nephrectomy. The procedure has been described below:

  • Nephrectomy - Nephrectomy is a surgical procedure in which all or parts of the kidney are removed. It might be done to remove the tumor of the kidneys and the surrounding structures. The extra kidney in the urinary system is usually removed by nephrectomy, and the patient is kept on follow-ups for a few weeks.

Which Disorders Are Associated With Supernumerary Kidneys?

Supernumerary kidneys do not cause problems unless associated with disorders like hydronephrosis, pyelonephritis, and vaginal atresia. The disorders associated with supernumerary kidneys are listed below:

1. Hydronephrosis - When the urine cannot exit the body due to urinary tract obstruction, kidney stones, ureteral strictures, or kidney tumors, it flows back to the kidneys. As a result, the pressure on the kidneys increases resulting in hydronephrosis.

2. Pyonephrosis - Pyonephrosis usually occurs when the stagnant urine becomes infected and pus forms in the kidneys. It is a serious condition and needs to be treated at the earliest.

3. Vaginal Atresia - It is a congenital condition in which the female reproductive organ, known as the vagina, is either closed or absent. Vaginal atresia does not occur alone and is commonly associated with supernumerary kidneys.

Conclusion:

A supernumerary kidney is a rare anomaly of the urinary system, and only 100 cases have been reported in the medical literature. Normally, the human body comprises two kidneys that are present below the rib cage. They carry out several important functions of the body and help the body get rid of waste products and toxins. Supernumerary kidneys are usually present by birth and might be incidentally diagnosed on an ultrasound. The patient has no symptoms, and the condition might go unnoticed. The extra kidney can be present above, below, or behind the normal kidneys, but they have their own blood supply. The problem arises when the disorders like hydronephrosis, pyonephrosis, and vaginal atresia are associated with a supernumerary kidney. In that case, the patient experiences fever and abdominal pain. However, the patient need not worry as surgical intervention is rarely required in the case of supernumerary kidneys. Consult the doctor soon to learn more about supernumerary kidneys and their associated problems.