It is possible for a person to have four kidneys, a condition known as a supernumerary kidney. This is a congenital anomaly, meaning it is present from birth. While individuals typically have two kidneys, the presence of an additional kidney is an uncommon occurrence, resulting from developmental variations before birth.
Understanding Supernumerary Kidneys
A supernumerary kidney is a distinct, additional kidney that develops independently from the two typically present kidneys. This extra organ possesses its own separate blood supply, collecting system, and a unique encapsulated parenchyma, distinguishing it as a complete renal unit. It is important to differentiate this from a duplicated collecting system, where a single kidney has two ureters or a split within its own internal drainage, rather than being an entirely separate organ. Supernumerary kidneys may also show reduced excretory function.
How and Why They Form
Supernumerary kidneys originate from an anomaly during fetal development, specifically involving the formation of the urinary system. Normally, kidneys develop from an outgrowth of the mesonephric duct, known as the ureteric bud. In cases of a supernumerary kidney, an extra ureteric bud can develop from this duct, leading to the formation of an additional kidney. The precise reasons for this developmental error are not fully understood, but current understanding suggests they are multifactorial, potentially involving a combination of genetic or environmental influences during early pregnancy.
Detection and Health Considerations
Supernumerary kidneys are frequently discovered incidentally during imaging studies, such as ultrasound, CT scans, or MRI, performed for unrelated medical reasons, as many individuals with this condition remain without symptoms. When symptoms do arise, they can include fever, pain, or a palpable abdominal mass. The presence of an extra kidney itself does not inherently cause problems; however, its abnormal position or drainage can lead to complications. Potential issues include urinary tract infections, kidney stones, and hydronephrosis, which is the swelling of a kidney due to urine backup. Rarely, tumors may also develop within a supernumerary kidney.
Living with an Extra Kidney
For individuals found to have a supernumerary kidney that is not causing any symptoms or complications, specific treatment is generally not required. Regular monitoring, including periodic ultrasound examinations, urine analysis, and blood tests, may be recommended to track the kidney’s condition.
If complications do arise, such as recurrent infections or kidney stones, interventions may become necessary. These can range from medication for infections to procedures for stone removal. In rare instances, particularly if the extra kidney is non-functional or consistently causing severe issues, surgical removal (nephrectomy) might be considered. The prognosis for affected individuals, especially those who remain asymptomatic, is generally favorable.