An individual can be born with three kidneys, a condition medically termed a supernumerary kidney. This rare congenital anomaly means a person possesses an additional, fully formed kidney. Understanding this unusual condition involves exploring its nature, how it is typically discovered, and the approaches to managing life with an extra kidney.
The Phenomenon of Supernumerary Kidneys
A supernumerary kidney is a distinct extra kidney with its own encapsulated tissue, separate blood supply, and independent collecting system, differentiating it from a duplicated collecting system within a single kidney. This anomaly is exceptionally rare, with fewer than 100 cases documented in medical literature globally. Such rarity makes its true incidence difficult to estimate, though one analysis based on CT imaging suggests a prevalence of approximately 1 in 26,750 individuals.
This development originates during early embryonic stages, around the fifth to seventh week of gestation. It occurs when there is an abnormal division of the nephrogenic cord into two metanephric blastemas, or a premature splitting of the metanephric bud. This developmental error results in the formation of an extra ureteric bud, which then induces the growth of an additional kidney alongside the two typical kidneys.
The supernumerary kidney can be completely separate or, in some instances, may be fused to one of the native kidneys by fibrous or parenchymal tissue. Typically, this accessory kidney is smaller than the normal kidneys and is often located lower than the ipsilateral kidney, frequently on the left side.
Identifying an Extra Kidney
A supernumerary kidney often goes unnoticed because individuals are frequently without symptoms. Discovery commonly occurs incidentally during imaging studies for unrelated medical concerns.
When symptoms arise, they are usually a result of complications associated with the extra kidney. These can include abdominal or flank pain, fever, or a palpable mass in the abdomen. Other potential, though less common, symptoms might involve recurrent urinary tract infections, the formation of kidney stones, or blood in the urine.
Diagnosis relies on various imaging techniques. Ultrasound is often an initial tool for morphological characterization, while computed tomography (CT) scans are frequently preferred for definitive diagnosis due to their ability to clearly visualize the supernumerary kidney’s distinct features. Magnetic resonance imaging (MRI) and intravenous urography are also valuable in confirming the presence and assessing the characteristics of an extra kidney.
Managing Life with an Extra Kidney
The functionality of a supernumerary kidney varies among individuals; it can be fully functional, have reduced excretion, or even be atrophic. Despite its presence, the extra kidney may not always contribute significantly to overall renal function.
While many individuals remain asymptomatic, the supernumerary kidney can be prone to complications. These include hydronephrosis, which is the swelling of a kidney due to urine backup, and recurrent infections like pyelonephritis. Stone formation is another common issue, and in rare instances, tumors such as renal cell carcinoma or Wilms’ tumor can develop within the accessory kidney.
Management is primarily guided by the presence and severity of symptoms and complications. For asymptomatic individuals, regular monitoring through imaging studies, such as ultrasound and CT scans, along with urine and blood tests, is often recommended to track the kidney’s condition. This observational approach helps ensure any potential issues are identified early.
Surgical intervention, such as removal, is generally reserved for cases where it causes significant symptoms, repeated infections, or other complications. Before surgery, detailed imaging like CT or MR angiography is crucial to map the unique vascular supply of the extra kidney, ensuring a safe and effective approach.