|Classification and external resources|
Fusion abnormalities of the kidney can be categorized into two groups: horseshoe kidney and crossed fused ectopia. The 'horseshoe kidney' is the most common renal fusion anomaly.
In patients with this condition, the central portion of the kidney may be found just inferior to the inferior mesenteric artery because the normal embryologic ascent of the kidneys is arrested by its presence in people with central fusion of the kidneys. Horseshoe kidney is often asymptomatic, though persons affected by this condition may experience nausea, abdominal discomfort, kidney stones and urinary tract infections at greater frequency than those without renal fusion. There is currently no treatment for renal fusion other than symptomatic treatment.
Imaging Findings - The 2 kidneys on opposite sides of the body with the lower poles fused in midline. Midline or symmetrical fusion (90% of cases). May be missed on US, therefore pay careful attention to identification of lower poles of kidneys. Renal long axis medially orientated, Lower poles with curved configuration, elongation and poorly-defined Isthmus crosses midline anterior to spine and great vessels. US for diagnosis in utero IVP followed by CT or scintigraphy for pre-operative assessment
Variant arterial supply - Bilateral renal arteries, Inferior mesenteric Artery, Arteries arising from aorta or common iliac, internal iliac, external iliac or inferior mesenteric arteries.
The lower poles of these kidneys fuse in the midline anterior to the aorta and spine. The isthmus is usually located at L4/5 level between the aorta and IMA.
Nuclear medicine (DMSA) scan confirms horseshoe kidney with fusion of both renal lower poles.
While most cases of horseshoe kidneys are asymptomatic and discovered upon autopsy, the condition may increase the risk for:
- Kidney obstruction – abnormal placement of ureter may lead to obstruction and dilation of the kidney.
- Kidney infections – associated with vesicoureteral reflux.
- Kidney stones – deviant orientation of kidneys combined with slow urine flow and kidney obstruction may lead to kidney stones.
- Kidney cancer – increased risk of renal cancer, especially Wilms' tumor, transitional cell carcinoma, and an occasional case report of carcinoid tumor. Despite increased risk, the overall risk is still relatively low.
Notable persons with this condition
- Mel Gibson is affected with this condition.
- Sam Kinison, a popular American comedian, also had this condition. 
- Natalie Baitson, famous singer from Gibraltar 
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- de Hoog JP, Murray S and Chou W (2010). Horseshoe kidney and primary renal carcinoid tumour: a case report of a rare entity. Grand Rounds 10 46–50 grandrounds-e-med.com
- Kleta R, Brämswig JH (2000). "Horseshoe kidney and Turner syndrome". Nephrol. Dial. Transplant. 15 (7): 1094. doi:10.1093/ndt/15.7.1094-b. PMID 10862660.
- "Renal Pathology". Retrieved 2008-11-26.