Horseshoe Kidney - A Case Report

Introduction

Horseshoe kidney is one amongst the common anomalies found in almost 1 in 400 people.¹ In this anomaly, two lower poles of the kidney are fused together.

Horseshoe kidney anomaly occurs between 7 and 9 weeks of gestation. The intermediate mesoderm which gives rise to the metanephric blastema does not separate. Nephrogenesis proceeds, as the ureteric bud develops cranially, even as they come in contact with the merged nephrogenic cords.²

In the beginning, the developing kidney is a pelvic organ which progressively ascends to a higher level. However, with growth of the embryo, the ascension of the kidney is obstructed because the isthmus of the kidney communicates with the origin of the inferior mesenteric artery.³ The renal pelves are oriented anteriorly because the fusion prevents the normal posterior rotation of the kidney. Typically, lower poles of kidney are fused together leading to the formation of parenchymatous isthmus.³ Upper pole and mid fusions are rare.

Even though the horseshoe kidney produces no serious complications, it can often be accompanied by various vascular and genitourinary anomalies.⁴ It is clinically vital to be conscious of these anomalies. In most cases of horseshoe kidney, it is not discovered till autopsy.

Case Presentation

The horseshoe kidney was observed during routine PG dissection on abdomen of male cadaver, post careful removal of the perirenal fat for studying the anatomy of kidney.

The right and left kidney were fused at their lower poles by a parenchymal isthmus ventral to abdominal aorta. The isthmus was oriented downwards in the median plane (Figure 1).

The horseshoe kidney was supplied by three renal arteries. The right renal artery originated directly from right side of abdominal aorta, and it ran downwards behind the inferior vena cava to divide into anterior and posterior divisions. These branches further divided to supply the apical, upper, middle, lower and posterior segments of right part of the horseshoe kidney, respectively. The left renal artery began from left side of aorta underneath the beginning of superior mesenteric artery and followed course of right renal artery. An accessory renal artery originated directly from abdominal aorta at the same level of origin of right common iliac artery and entered the right kidney at its lower pole (Figure 2).

The isthmus was situated anterior to abdominal aorta and inferior vena cava. Both renal hila opened anteriorly. From each pelvis, a single ureter originated which ran downwards onto the anterior surface of horseshoe kidney to reach urinary bladder as usual. The inferior vena cava was located behind the isthmus and the lower poles of both kidneys.

Discussion

In the present case review, the horseshoe kidney is the outcome of an anomalous fusion of the inferior pole to create the parenchymatous isthmus. Its characteristics include an isthmus in the median plane, an anterior facing hilum, the ureters on the anterior surface of horseshoe kidney and presence of one accessory renal artery at lower pole of right kidney.

This developmental anomaly usually occurs between 7 to 9 weeks of gestation.⁵ The intermediate mesoderm, from which the metanephric blastema arises, does not separate. It comes in contact with the fused nephrogenic cords, as the ureteric bud grows cranially and nephrogenesis continues. With the development of embryo, the ascension of the kidney is obstructed as the isthmus of the kidney communicates with inferior mesenteric artery. The fusion prevents normal posterior rotation of the kidney, leading to the renal pelves orienting anteriorly. Fusion generally takes place at the lower poles.

Pelvi-ureteric junction obstruction is the most commonly observed abnormality of horseshoe kidneys. Individuals are predisposed to hydronephrosis, infection, vesicoureteral reflux as well.4 Hydronephrosis is caused by pelvi-ureteric junction obstruction, which could be because of the high origin of the ureter at renal pelvis, crossing of ureter on top of the isthmus, renal stones and infection.

Horseshoe kidney has the incidence of concomitant vascular or genitourinary anomalies, vesicoureteric reflux, hypospadias and undescended testis.⁵ The presence of horseshoe kidney is especially important in renal surgical procedures, renal transplants, or other surgical and endovascular techniques on aorta because of the abnormal complexity of the kidney, renal blood vessels and its collecting system. Therefore, the morphological structure and variations of kidney are factors to be considered. The bulky isthmus located in front of abdominal aorta and its bifurcation, in the horseshoe kidney can cause significant difficulty in medical and surgical management.

Horseshoe kidney is a congenital abnormality, often asymptomatic throughout life but occasionally may predispose the patient to numerous complications including pelvi-ureteric obstruction, hydronephrosis, renal stones, infection, malignancies and loss of renal function. Urologists face technically difficult cases which are not responsive to standard operative procedures, which in turn affect the quality of life of the patient and long-term functionality of horseshoe kidney. This review demonstrates that the knowledge of such anomalies as described here is especially important in planning and conducting surgical procedures.

Conflicts of Interest

None