Horseshoe Kidney

General Considerations

• Most common fusion abnormality of the kidney
• Fusion is at lower pole in 90% of cases
• The majority of each kidney lies on its own side of the spine
  • In crossed fused ectopia, both fused kidneys lie on the same side of the spine
• May occur as isolated anomaly or with other anomalies (1/3), such as
  • Reflux, hypospadias, retrocaval ureter, imperforate anus, Meckel diverticulum

Clinical Findings

• About 1/3 are asymptomatic
• When present, symptoms stem from hydronephrosis, stones, infection
• Vague abdominal pain may be most common presenting symptom

Imaging Findings

• CT is probably study of choice now
• Isthmus (fused portion) is usually functioning renal parenchyma but can be fibrous
  • Isthmus is anterior to aorta and inferior vena cava and posterior to inferior mesenteric artery
• Renal scintigraphic scanning may also demonstrate whether the isthmus contains functioning tissue of not
  • Sometimes incidentally diagnosed on bone scans
• Renal pelvis is usually rotated anteriorly and ureters arise anteriorly or laterally
• If both upper and lower poles fuse, called pancake or doughnut kidney
• In only 1/3 of cases is there a single renal artery for each kidney
  • In most cases, one or both kidneys have 2-3 renal arteries and isthmus receives its supply from renal artery or aorta
• Axis of kidneys is tilted such that upper poles are more lateral than lower poles
  • Lower pole calyces lie medial to the ureters
• Renal pelvis may be extrarenal and large
• There may be evidence of hydronephrosis from UPJ obstruction

Treatment

• UPJ obstruction may be treated surgically
• Stones may be treated with lithotripsy

Complications

• Ureteropelvic junction obstruction
• Recurrent infections (frequent)
• Recurrent calculus formation (frequent)
• Increased incidence of Wilms tumors, transitional cell carcinoma and renal carcinoids

Prognosis

• Normal survival rate with isolated abnormality

Horseshoe Kidney. Enhanced axial CT scan of abdomen at two near-contiguous levels shows a horseshoe-shaped kidney (blue arrows) which has functioning
renal parenchyma in the isthmus that crosses the midline (red arrows).
The ureter is seen anteriorly on the left (yellow arrow).
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eMedicine  Horseshoe Kidney    Abid Irshad, A; Ackerman, S; Ravenel, J