thalidomide, ethanol, ACE inhibitors, cocaine, gentamicin, corticosteroids, NSAIDs, and vitamin A) have been hypothesized. Impairment of a developing embryos nephrogenic cell migration or abnormal migration of the kidneys due to fetal structural abnormalities is another potential factor. However, no definitive genetic cause has been identified. Pathophysiology
Kidneys are normally located in the retroperitoneal space between the T12 and L3 vertebrae after ascending from the pelvis during development to rest underneath the adrenal glands. In patients with this condition, the horseshoe kidney ascent is commonly arrested by the inferior mesenteric artery due to the central fusion of the kidneys. However, this is present in only 40% of cases, and, in 20% of cases, the fused kidney remains in the pelvis. Its ascension may also be restricted by its own renal artery. Additionally, during normal development, the kidneys undergo a 90 degree medial rotation while ascending. However, due to the renal fusion, this rotation is impaired resulting in abnormal placement of the ureters. This in turn can lead to urinary stasis and drainage issues. Furthermore, approximately 70% of kidneys in normal individuals are supplied by a single renal artery with the remaining 30% having embryonic collateral or accessory arteries. With horseshoe kidneys, the majority are supplied by derivatives of the abdominal aorta or common illiac arteries depending on the final position of the kidneys. Diagnosis
Horseshoe kidneys are commonly diagnosed incidentally on abdominal imaging.
For this reason, prior to any treatment with shockwave lithotripsy, a UPJ obstruction must first be ruled out as it significantly impair successful treatment. For stones that are less than 1.5 cm, ureteroscopy and shockwave lithotripsy can be first utilized. For stones larger than 1.5 cm or when previous treatment has failed, the stones can instead be removed through a minimally invasive procedure known as percutaneous nephrolithotomy.Compared to patients with normal kidneys, patients with horseshoe kidneys who undergo treatment with percutaneous nephrolithotomy experience no difference in complications or stone clearance.Patients will also typically require imaging before any abdominal surgery as the vascular supply to the abnormal kidney can be highly variable between patients. Additionally, the horseshoe kidneys can have a close association with colon which can increase risk of bowel injury. Epidemiology
There is an incidence of 1 in every 500 individuals within a normal population.Males are more likely to develop a horseshoe kidney with a preponderance of 2:1.Certain genetic diseases can predispose patients to developing a horseshoe kidney:

Edwards Syndrome: 67%
Turner Syndrome: 14-20%
Down Syndrome: <1%

Notable cases
Mel Gibson is affected with this condition. Sam Kinison, an American comedian, also had this condition. Robert Rowan a member of the Anglican clergy was afflicted by the condition. References


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