What Is a Horseshoe Kidney?
Normally, there are two separate kidneys located deep in the back under the protection of abdominal muscles and ribs. With a horseshoe kidney, the two kidneys are actually fused together (thus giving it a horseshoe appearance). The tissue connecting the kidneys is called the isthmus.A horseshoe kidney is remarkable because of its unusual location, its abnormal orientation, its unusual blood supply, and the problematic placement of the ureters into it. All of this can lead to a higher risk of kidney disease and complications.
Risk Factors
Although horseshoe kidneys can be seen in certain genetic syndromes and associated with various congenital genitourinary anomalies, they are often isolated events. They are predominantly seen in males and sometimes they can run in a family (but not usually). But otherwise, there are no obvious risk factors.
Diagnosis & Treatment
Horseshoes kidneys don’t usually cause symptoms by themselves. However, medical conditions or complications associated with them can cause significant symptoms. For many people, they are found incidentally during a radiology test done for another reason or on autopsy.When a horseshoe kidney does cause a problem, it is often quickly identified through various radiology studies (usually a kidney ultrasound or abdominal CT). Treatment for the horseshoe kidney itself is controversial and not usually indicated. Instead, treatment is usually directed at the complications caused by it.
Complications
Although a horseshoe kidney can go unnoticed and not cause a problem, it can result in a higher risk for kidney disease and complications:- Kidney Obstruction: Abnormal placement of the ureters can lead to obstruction and dilation of the kidney. Whether this is significant or not often requires undergoing a special nuclear kidney scan.
- Kidney Infections: Horseshoe kidneys are often associated with vesicoureteral reflux (VUR). Normally when the bladder contracts, urine is prevented from going back into the ureters. With VUR, urine can reflux back up into the ureters and kidneys, thus leading to a higher risk of kidney infections.
- Kidney Stones: The unusual orientation of the kidney combined with slow urine flow or obstruction, can predispose to kidney stones.
- Kidney Cancers: There is a higher risk of kidney cancer with a horseshoe kidney. The most common are: Wilm’s tumor, transitional cell cancer and carcinoid tumor. Despite the higher risk, the overall risk is relatively low. As a result, there are currently no formal recommendations for regular cancer screening for those with a horseshoe kidney.
Special Concerns
In addition to the complications above, there are certain risks that a horseshoe kidney poses:- Trauma Risk: Horseshoe kidneys are usually misplaced and not well protected by the ribs. There is a real risk for it being compressed or fractured across the spine. Avoidance of sports where kidney injury may occur is usually recommened.
- Surgery Risk: Horseshoe kidneys often sit in front of the great blood vessels in the abdomen. This plus its unusual blood supply make it a risk when performing surgery involving the abdominal aorta (e.g. aneurysm repair). Pre-operative angiograms of the kidney can be very important.
Prognosis & Outcome
Overall, the prognosis of a horseshoe kidney is excellent. There is no evidence that affects survival. With careful attention to preventing kidney injury as well as timely recognition of associated complications, it can be a relatively benign medical condition.
Sources
- Jeong Yeon Cho. “Congenitital Anomalies of the Upper Urinary Tract”. Radiology Illustration: Uroradiology. Ed Seung Hyup Kim. Philadelphia: Saunders, 2003. 29-31.
- Ronald J. Zagoria. “The Kidney and Retroperitoneum: Anatomy and Congenital Abnormalities”. Genitourinary Radiology: The Requisites. Philadelphia: Mosby, 2004. 51-79.