Supernumerary kidneys are a rare congenital anomaly of the urogenital system, where there are one or more accessory kidneys present. Fewer than 100 cases have been reported of supernumerary kidney. A fused supernumerary kidney is even rarer.
Educational Goals / Teaching Points
This exhibit presents a rare case of fused supernumerary kidney and discusses imaging findings and treatment options.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
A 27-year-old male with abdominal pain and mild abdominal tenderness. Contrast-enhanced abdominal CT showed two kidneys on the right side with partial fusion and malrotation of the inferiorly located kidney. Also, superiorly positioned right kidney’s pelvicalyceal system was directed medially, and the inferiorly positioned kidney's pelvicalyceal system was directed laterally. Both right proximal ureters joined to form a single ureter and drained through the bifid ureter. The superior kidney received its arterial supply from a single renal artery from the abdominal aorta. The more inferior kidney was supplied by two renal arteries, with the superior branch from the abdominal aorta and the inferior branch from the right common iliac artery. Both the kidneys on the right side drained via two different renal veins into the IVC. The left kidney demonstrated no anatomical variation. Findings consistent with fused right supernumerary kidney.
In most cases, supernumerary kidneys are on the left and present caudal to the native kidney. In our case the supernumerary kidneys are on the right side. There are 2 types of supernumerary kidney present. The first type drains by two separate ureters and the second type drains by bifid ureter. When a bifid system is present, the supernumerary kidney lies caudally. However, when a separate ureter is seen, the supernumerary kidney is usually located cranially in relation to the normal kidney. In our case, a bifid system is present, so the supernumerary kidney lies caudally in relation to the normal kidney which was located cranially. If the supernumerary kidney is located cranially in relation to the normal kidney, the ureter is usually completely separate and may enter the bladder ectopically, in which case the Weigert-Meyer rule may be followed and the ureter may insert medially and inferiorly into the bladder. Sometimes the ureter of the supernumerary kidney may be associated with an ectopic opening, such as into the vagina. In this case, it may present with symptoms of urinary incontinence. The treatment for this condition depends on the symptoms and the function of the supernumerary kidney. If the patient is asymptomatic, no treatment is required but regular follow-up may be advised. If the kidney is diseased or nonfunctional, nephrectomy is usually the preferred procedure. In our case, the patient’s symptoms improved in the ED. The patient was discharged with a primary care physician follow-up. Supernumerary kidney is a very rare condition. Symptoms do not always lead to diagnosis. It is usually an incidental finding in imaging. Imaging using CT and US are usually required for evidence. Treatment varies with symptoms and function of supernumerary kidneys.