Horseshoe kidney is the most common renal fusion anomaly, occurring in approximately 1 in 400 births (1).

The right and left kidneys are fused in the midline by a parenchymal or fibrous isthmus. During gestation, the metanephric blastema abnormally migrates toward the midline, leading to contact and fusion of the lower poles. The normal ascent of the kidney is arrested by the inferior mesenteric artery at the level of the L3 or L4 vertebra, and the kidney fails to normally rotate. Consequently, the renal pelvis is ventrally placed and the ureters often course over the isthmus.

The vascular supply to the horseshoe kidney may be complex. The isthmus usually has a separate blood supply. The blood supply to the isthmus may arise from the main renal arteries or it may branch from the inferior mesenteric, iliac, or sacral arteries (2,3). In most cases, there are multiple arteries and veins that supply each kidney.

Horseshoe kidneys are frequently associated with other congenital anomalies. Anomalies involving the skeletal, cardiovascular, and central nervous systems are common. The most frequently associated genitourinary anomalies are hypospadias, crypt-orchidism, bicornuate uterus, septate vagina, polycystic renal disease, ureteral duplication, and vesicoureteral reflux (4). Horseshoe kidneys are found in 20% of patients with trisomy 18 and 60% of patients with Turner's syndrome (5,6).

Although most horseshoe kidneys do not cause symptoms, nephrolithiasis, ureteropelvic junction obstructions, and renal masses are the most frequent findings that require surgery (7).

The location of the kidney and the isthmus make laparoscopy challenging. However, laparoscopy is becoming the standard for surgical management of many renal diseases, and laparoscopic pyeloplasties and heminephrectomies can be successfully performed in patients with a horseshoe kidney.

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