Crossed renal ectopia

Crossed dystopia (syn.unilateral fusion cross fused renal ectopia) is a rare form of renal ectopia where both kidneys are on the same side of the spine. In many cases, the two kidneys are fused together, yet retain their own vessels and ureters.[1] The ureter of the lower kidney crosses the midline to enter the bladder on the contralateral side. Both renal pelvis can lie one above each other medial to the renal parenchyma (unilateral long kidney) or the pelvis of the crossed kidney faces laterally (unilateral "S" shaped kidney). Urogram is diagnostic.

Ectopic crossed fused kidney in a fetus approx. 34 weeks

The anomaly can be diagnosed through ultrasound of urography, but surgical intervention is only necessary if there are other complications, such as tumors or pyelonephritis.