Ipsilateral Renal Ectopia

The pelvic kidney lies adjacent to the sacrum and distal to the aortic bifurcation, whereas the lumbar kidney is in the sacral fossa anterior to the iliac vessels, and the abdominal kidney is above the iliac crest adjacent to the L2 vertebra. Although these ectopic kidneys are small and have fetal lobulation, the length of the ureter conforms to the position of the kidney and usually lies in the normal anatomic position. The arterial supply can arise from the distal aorta or its bifurcation and can include one or more aberrant arteries arising from the iliac or inferior mesenteric arteries.

Horseshoe Kidney

Horseshoe kidney, thought to occur in 0.25% of the population, is probably the most common of all renal fusion abnormalities and is twice as common in men as it is in women. Horseshoe kidneys result when the metanephric masses fuse anteriorly in the midline. Their normal bilateral ascent is presumed to be blocked by the inferior mesenteric artery, and the associated impaired medial orientation causes the renal hila and collecting systems to be rotated ventrally, in turn inducing the ureters to lie anterior to the renal isthmus (Figure 1A).

The horseshoe kidney usually consists of two separate renal masses lying vertically on either side of the midline and connected at their respective lower poles by an isthmus that crosses anterior to the aorta near the origin of the inferior mesenteric artery. This can pose a particular challenge during AAA repair (see Figure 1B). Although occasionally fibrous and avascular, the isthmus may consist of substantial renal parenchyma and its blood supply may be asymmetric, making simple division of the isthmus in the midline hazardous. Furthermore, the collecting systems may also be asymmetric and can extend anteriorly and across the midline in the region of the isthmus. Arterial and venous anomalies are common.

Associated arterial anomalies occur in 60% to 80% of horseshoe kidneys. In the author’s series, renal artery anomalies were encountered in 14 patients (74%), whereas the remaining five patients (26%) had only two main renal arteries in the normal location. Division of the renal isthmus was avoided in all patients of the author’s series to avoid the risk of urinary fistula and graft sepsis, because 13% of patients with horseshoe kidney are reported to have chronic urinary tract infection.

Crossed Renal Ectopia

If the fused metanephric masses ascend together on one side, in contrast to horseshoe kidney development, then crossed renal ectopia can result. In this anomaly, the ectopic kidney is located on the side contralateral to its ureterovesical junction and, in most instances, is fused to the inferior portion of the ipsilateral kidney (see Figure 1C). Fusion and crossover of the left kidney to the right side is the most common form of this variation and results in a single fused renal unit, with the collecting system lying anterior to the aorta and at least one of the ureters crossing the midline anterior to the aorta, usually above the second sacral vertebra. The arterial and venous anatomy often consists of multiple vessels in unpredictable locations. Crossed renal ectopia has been further classified depending on the shape assumed by the fused renal masses (see Box 1), but all forms are managed the same way during aortic reconstruction.