Crossed Renal Ectopia

Definition of Crossed Renal Ectopia

Crossed renal ectopia is the location of the kidney on the contralateral side in respect to the ureteral orfice 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):

L-shaped kidney:

Transversal position of the crossed kidney, the uncrossed kidney lies in normal position with the lower pole in contact to 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 pelvis are directed anteriorly.

S-shaped kidney:

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

Unilaterally fused kidneys with inferior ectopia:

Most commen form of crossed renal ectopia. Both kidneys are in longitudinal position, the upper pole of the crossed kidney is fused to the uncrossed kidney (lower pole). The renal pelvis are directed anteriorly [fig unilateral fused kidneys with inferior ectopia].

Solitary crossed renal ectopia:

the uncrossed kidney is missing.

fig. angiography of unilaterally fused kidneys with inferior ectopia

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 can be seen on the left side. Angiography (below) shows the abnormal arterial supply of the crossed kidney with numerous additional arteries. By courtesy, 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 of crossed renal ectopia is unclear.

Signs and Symptoms of Crossed Renal Ectopia

Vesicoureteral reflux (VUR) in 20%. Only in solitary crossed renal ectopia, there is an increased risk for malformations of the musculoskeletal system or the genital organs.