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Crossed Renal Ectopia

Definition of Crossed Renal Ectopia

In crossed renal ectopia, a kidney is located on the contralateral side in relation to its ureteral orifice in the bladder. The term crossed renal dystopia is used synonymously. The crossed kidney is often fused with the uncrossed kidney, which is termed crossed fused renal ectopia [fig. examples of crossed renal ectopia].

Depending on the configuration and fusion, the following forms are distinguished (McDonald and McClellan, 1957):

Long kidney:

The kidneys are positioned one above the other, and both renal pelvises are directed medially. This is the most common form of crossed fused renal ectopia [fig. intravenous urography of crossed renal ectopia and intravenous urography and angiography of crossed renal ectopia].

Sigmoid or S-shaped kidney:

The renal pelvis of the crossed kidney points toward the crossed side, and the kidneys are positioned one above the other.

L-shaped kidney:

The crossed kidney lies horizontally below the uncrossed kidney.

Cake or ring kidney:

There is extensive fusion of both kidneys; the renal pelvises are usually directed anteriorly.

Bilaterally crossed renal ectopia:

Both kidneys are crossed without fusion; this is extremely rare.

Solitary crossed renal ectopia:

The orthotopic contralateral kidney is absent. This form is extremely rare and is often associated with other malformations.

Crossed renal ectopia (long kidney): The most common form of crossed renal ectopia. The crossed and uncrossed kidneys are positioned one above the other. Intravenous urography (top) shows an empty left renal fossa, two kidneys positioned one above the other on the right, a ureter is visible on the left side. Angiography (bottom) demonstrates the abnormal arterial supply of the crossed kidney with numerous additional arteries. With kind permission, Dr. G. Antes, Kempten.

Intravenous urography of crossed renal ectopia (long kidney) on the right: empty left renal fossa, two kidneys positioned one above the other on the right, and the ureter of the lower kidney crossing to the left side. With kind permission, Dr. N. Dreger and Prof. Dr. S. Roth, Wuppertal.

Epidemiology:

1:1000 to 1:2000. The long kidney, in which the crossed kidney is located inferiorly, is the most common form. Crossing from left to right is more common.

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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