Learning Radiology xray montage

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


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


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


  • Normal survival rate with isolated abnormality

orseshoe 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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For these same photos without the arrows, click here and here


eMedicine  Horseshoe Kidney    Abid Irshad, A; Ackerman, S; Ravenel, J