Horseshoe Kidney

Horseshoe kidney is the commonest congenital anomaly involving the urogenital tract. It is estimated that one in every 500 children suffers from this condition. In the fetus, once the kidneys are developed, they rotate in a manner that their axes diverge and the ureters arise from their medial aspect. However, in case of horseshoe kidneys, there occurs a mal-rotation of the kidneys. The process of rotation is incomplete. Hence, there is convergence of the longitudinal axes of the kidneys and the ureters leave the kidneys from their ventral aspect. The lower poles of the kidneys remain fused giving an appearance of a horseshoe. Hence, the name horseshoe kidney.The bridge that connects the lower poles of the kidneys is composed of either renal parenchyma or fibrous tissue. As the bridge usually lies ventral to the aorta, the condition is often misdiagnosed as lymphoma or any other retroperitoneal tumor.The position of a horseshoe kidney may be variable. In certain cases, it is found in its normal position; while in other cases, it may lie inside the pelvis.

A Horseshoe kidney is often associated with other congenital anomalies

We know that horseshoe kidney is a congenital anomaly. However, this congenital anomaly is usually not found in isolation. Rather, it is often found to be associated with other congenital problems of the central nervous system, the cardiovascular system or the genitourinary system. Some of the common conditions found along with horseshoe kidney are:

• Renal stones
• Hydronephrosis
• Wilm’s tumor
• Renal cancer
• Polycystic renal disease
• Hydrocephaly
• Spina bifida

When should one suspect a horseshoe kidney during ultrasonography?

The presence of a horseshoe kidney should be suspected under following circumstances:

• When the lower poles of the kidneys cannot be visualized properly
• When the kidneys appear unusually small on ultrasonography.
• When the longitudinal axes of the kidneys appear to converge.
• When one can see a mass ventral to the aorta

According to radiologists, the diagnosis of a horseshoe kidney is often missed if ultrasonography is done when the patient is in the prone position. According to them, the examination should be done first in the supine position and then after turning the patient left or right.

Some special points to be remembered in patients with horseshoe kidney

While dealing with a patient with a horseshoe kidney, following points should be kept in mind:

• Usually the pelvi-calyceal system is minimally dilated.
• In certain cases, there may be narrowing of the ureters where they cross the bridge between the two kidneys. This ureteropelvic stenosis may give rise to hydroureter and hydronephrosis.
• Renal stones are found in many such cases. There may be accessory renal arteries.

Symptoms of horseshoe kidney

This condition may often go undiagnosed. However, when associated problems of the cardiovascular, nervous or genitourinary system arise, symptoms may develop accordingly.

Diagnosis of horseshoe kidney

The main investigation for diagnosing a horseshoe kidney is ultrasonography. Other diagnostic procedures which can be useful include:

• Voiding cysto-urethrogram
• Intravenous pylogram
• Blood tests to check renal functioning.
• Urine tests including culture

Treatment of horseshoe kidney

Only symptomatic patients of horseshoe kidney require treatment. Surgery remains the mainstay of treatment. It is usually performed depending upon the factors that produce the symptoms. The anomalous blood supply should always be kept in mind while performing the surgery. Reference:“Horseshoe Kidney,” by Anna-Maria Nahm and Eberhard Ritz, published in 1999 in the journal Nephrology, Dialysis and Transplantation, accessed on July7, 2015, retrieved from:http://ndt.oxfordjournals.org/content/14/11/2740.full