Horseshoe kidney is characterized by a fusion of the inferior renal poles. Instead of having two kidneys, the patient will have one kidney with a "U" shape.
During fetal development, the kidney moves proximally. If horseshoe kidney occurs, the kidney will be trapped under the inferior mesenteric artery.
Horseshoeing of the kidney doesn't interfere with renal function. Patients present with normal renal function.
Horseshoe kidney can be seen in 14-20% of patients with Turner syndrome. This is the most common renal abnormality seen in patients with Turner syndrome.
The incidence of Horseshoe kidney is higher in patients with trisomy syndromes. These include Edward syndrome (67% cases), and Down syndrome (1% cases).
Ultrasound is the most common diagnostic tool used to visualize horseshoe kidneys. Diagnosis will be made with the presence of fusion of the kidney's isthmus which is seen in the inferior part of the kidney. It will be hard to be seen if malrotation occurs or there is an altered renal axis.
Horseshoe kidneys can cause abnormal positioning of the ureter. This frequently results in the stenosis of the ureteropelvic junction causing hydronephrosis.
Nephrolithiasis is one of the most common complications and is seen in 20-60% of patients with horseshoe kidneys. It is a result of a stone formation due to impaired drainage of the collecting system.
Infection is the other complication that may occur in patients with horseshoe kidney due to the presence of urine stasis resulting from ureteropelvic junction stenosis or stone formation.
Horseshoe kidney carries an increased risk of renal cancer. Renal cell carcinoma is the most common renal cancer type seen in these patients.
Horseshoe kidney has an excellent prognosis, and typically doesn't affect life expectancy. One-third of those with horseshoe kidney will have this disease discovered incidentally.
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