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Crossed Renal Ectopia

Definition of Crossed Renal Ectopia

Crossed renal ectopia is the location of the kidney on the contralateral side in relation to the ureteral orifice location at the bladder. Often, the crossed kidney is fused with the uncrossed kidney [fig. examples of crossed renal ectopia].

Several examples of crossed renal ectopia: A) Bilaterally crossed renal ectopia B) S-shaped kidney C) L-shaped kidney D) Disc kidney.

Depending on the form and fusion, different forms of crossed renal ectopia are possible (McDonald and McClellan, 1957):

Unilaterally fused kidneys with inferior ectopia:

Most common form of crossed renal ectopia. Both kidneys are in a longitudinal position; the crossed kidney's upper pole fuses to the uncrossed kidney's lower pole. The renal pelvises are directed anteriorly [fig unilateral fused kidneys with inferior ectopia].

S-shaped kidney:

Second most common form of crossed renal ectopia. Both kidneys are in a longitudinal position. The crossed kidney is inferior to the uncrossed kidney, and the renal pelvis is directed laterally. The uncrossed kidney is in a normal position.

L-shaped kidney:

Transversal position of the crossed kidney, the uncrossed kidney lies in a normal position with the lower pole in contact with the crossed kidney.

Disc kidney:

Crossed and uncrossed kidneys are fused with their medial borders; the lateral aspects are normal and create a disc shape. The renal pelvises point anteriorly.

Bilaterally crossed renal ectopia:

Both kidneys are crossed without fusion.

Solitary crossed renal ectopia:

The uncrossed kidney is missing.

Unilaterally fused kidneys with inferior ectopia: most common form of crossed renal ectopia. Intravenous urography (top) shows a missing kidney on the left. Both kidneys are positioned on the right side; a ureter is visible on the left side. Angiography (below) shows the abnormal arterial supply of the crossed kidney with numerous additional arteries. With kind permission, Dr. G. Antes, Kempten.

Epidemiology:

1:1000 to 1:2000. The most common form is unilaterally fused kidneys with inferior ectopia, slightly more often the crossing from left to right.

Etiology of Crossed Renal Ectopia

The etiology is not fully understood; proposed mechanisms include misdirected growth of the ureteric bud, disturbances of renal ascent, vascular barriers, and other mechanical factors.

Signs and Symptoms of Crossed Renal Ectopia

Usually asymptomatic; the diagnosis is often made prenatally or incidentally. Symptoms typically arise only when complications develop (hydronephrosis, UTI, VUR, or nephrolithiasis) or when associated malformations are present.

Diagnosis

• Ultrasound: Key findings are an empty renal fossa on one side and two kidneys or one large misshapen kidney on the contralateral side.
• CT or MRI: Additional cross-sectional imaging is useful when the anatomy is unclear, in the presence of hydronephrosis, or before interventional or surgical treatment.

Treatment of Crossed Renal Ectopia

Treatment is only necessary in the presence of symptoms or complications. In asymptomatic patients with urinary tract ectasia, imaging follow-up is advisable.

References

  Deutsche Version: gekreuzte Nierenektopie

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