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Horseshoe Kidney

Definition of a Horseshoe Kidney

A horseshoe kidney is the fusion of the lower poles of both kidneys ventral of the aorta, the fusion is called isthmus of the horseshoe kidney. It consists of connective tissue or renal parenchyma [see the following figures]. Review literature: (Kölln et al., 1972) (Stein and Desai, 2007).

Schematic drawing of a horseshoe kidney. (1) inferior mesenteric artery cranial to the isthmus.

Urography of a horseshoe kidney: With kind permission, Dr. G. Antes, Kempten.

Computed tomography of a horseshoe kidney:left figure: axial plane. Right figure: frontal plane. With kind permission, Dr. G. Antes, Kempten.

Epidemiology of a Horseshoe Kidney

Incidence 1:700. Male:female = 2:1.

Etiology of a Horseshoe Kidney

The fusion of the lower poles takes place before the rotation and the ascension of the kidneys, causing a ventral orientation of the renal pelvis and dorsal position of the calyceal system. The inferior mesenteric artery inhibits the ascension of the kidney. The vascular supply of the horseshoe kidney derives from the iliac vessels and the distal aorta. Due to the abnormal vasculature, horseshoe kidneys may develop an extrinsic ureteropelvic obstruction with hydronephrosis.

Signs and Symptoms of a Horseshoe Kidney

60% of patients with a horseshoe kidney do not develop any symptoms. Otherwise, hydronephrosis, nephrolithiasis, and infections are the most often complaints.

Malformations:

A horseshoe kidney is associated with other malformations (neural tube defect, heart defects, and musculoskeletal system). 5–10% of patients with horseshoe kidneys have additional urogenital anomalies. A horseshoe kidney is associated with Turner syndrome and trisomy 18.

Oncogenic risk:

The risk for Wilms tumor is doubled. Increased risk for the rare renal carcinoid in horseshoe kidneys.

Treatment of a Horseshoe Kidney

Nephrolithiasis:

All techniques of stone therapy can be used: extracorporeal shock wave lithotripsy (ESWL), ureteroscopy or percutaneous nephrolithotomy.

Hydronephrosis:

Depending on the renal function, pyeloplasty or heminephrectomy is the treatment of choice.

Tumors of the horseshoe kidney:

Treatment depends on tumor size, age of the patients, and suspected histology. Pay attention to the pathological vascular supply of the horseshoe kidney in treatment decisions.

References

  Deutsche Version: Hufeisenniere