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Accessory (Supernumerary) Kidney

Definition:

A supernumerary kidney is a very rare additional renal organ with additional renal function, its own blood supply, organ capsule, and collecting system. Both normally developed kidneys are present; the accessory kidney may partially drain through a common orifice with the ipsilateral normally developed kidney.

Epidemiology:

It is one of the rarest urinary tract anomalies; only case reports and small case series have been published (Bernik et al., 2001).

Etiology:

It is caused by abnormal division of the nephrogenic cord or by two separate ureteric buds with separate induction of metanephric tissue.

Signs and Symptoms:

Pain, fever, a mass, or arterial hypertension may originate from the supernumerary kidney.

Diagnosis:

If ultrasonography raises suspicion of an additional kidney, CT or MRI usually confirms the diagnosis and delineates the associated anatomy.

Therapy:

In asymptomatic patients with an additional kidney, treatment is generally not required; occasional imaging follow-up is appropriate. Surgical removal is indicated in the presence of symptoms, complications, or suspected malignancy.

References

Bernik et al. 2001. BERNIK, T. R.; RAVNIC, D. J.; BERNIK, S. F.; WALLACK, M. K.: Ectopic supernumerary kidney, a cause of para-aortic mass: case report and review.
In: American Surgeon
67 (2001), No. 7, pp. 657–659

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