•Horseshoe kidneys are susceptible to trauma and are an independent risk factor for the development of renal calculi and transitional cell carcinoma of the renal pelvis.

•Horseshoe kidneys are found in approximately

1in 400–500 adults.

•They are more frequently encountered in males (M:F 2:1).

•The vast majority of cases are sporadic, except for those associated with genetic syndromes.

•Horseshoe kidneys are frequently associated with both genitourinary and non-genitourinary malformations.

•Chromosomal/aneupliodic anomalies:

– Down syndrome

– Turner syndrome: up to 7 % have a horseshoe kidney

– Edward syndrome (trisomy 18): up to 20 % have a horseshoe kidney

– Patau syndrome (trisomy 13)

•Non-aneupliodic anomalies

– Ellis-van Creveld syndrome

– Fanconi anaemia

– Goltz syndrome

– Kabuki syndrome

– Pallister-Hall syndrome

– VACTERL association

•Horseshoe kidneys are asymptomatic and usually identified incidentally.

•They are however prone to a number of complications including:

– Hydronephrosis, secondary to pelviureteric junction obstruction

– Renal calculi

– Increased susceptibility to trauma

– Infection and pyeloureteritis cystica

– Increased incidence of malignancy

•Wilms tumour

•Transitional cell carcinoma

•Renal carcinoid

–Renovascular hypertension

•Associated abnormalities:

–It has been reported that one third of patients with horseshoe kidney have at least one other abnormality.

–The most commonly affected systems are the gastrointestinal, skeletal, cardiovascular and central nervous system.

–Ureteral duplication is reported to occur in 10 %

–VUR is reported to occur in 10–80 %.

–Multicystic dysplasia and autosomal dominant polycystic kidney disease has also been reported.

–Horseshoe kidney is present in 21 % of patients with trisomy 18 and in 7 % in those with Turner’s syndrome.

–Abdominal aortic aneurysms have been reported later in life .

–Hypospadias and cryptorchidism occurs in 4 % of males and bicornate uterus or septate vagina in 7 % of females.

•Outcomes depend on associated urological problems as horseshoe kidneys are usually asymptomatic.

•PUJ obstruction occurs in 30 % and is more often left-sided.

•Renal calculi occur in up to 20 % of horseshoe kidneys.

•Xanthogranulomatous pyelonephritis has been reported but is rare.

•There is an increased risk of malignancy in horseshoe kidneys in childhood.

–Wilms tumor occurs with a 1.5- to 8-fold increased risk and surgical management can be challenging.

–Renal cell carcinoma, transitional cell carcinoma, oncocytoma and carcinoid have all been described.

•The diagnosis of horseshoe kidney can be confirmed by ultrasound, intravenous urography and CT-scan/MRI.

•Horseshoe kidneys in themselves do not require any treatment, and patients have normal life expectancy.

•It is however important to recognize their presence prior to abdominal surgery or renal intervention for one of their many complications.

1.3.9Crossed Fused Renal Ectopia

•The second most common fusion anomaly is crossed renal ectopia.

•Crossed fused renal ectopia refers to an anomaly where the kidneys are fused and located on the same side of the midline.

•If during ascent, one kidney advances slightly ahead of the other, the inferior pole of one may come into contact with the superior pole of the lower kidney and fuse, resulting in crossed fused renal ectopia.

•The exact cause of this is not fully understood.

–Some evidence supports that an abnormally situated umbilical artery prevents normal cephalic migration.

–Another theory is that the ureteric bud crosses to the opposite side and induces nephron formation in the contralateral metanephric blastema. The result is a single renal mass with two collecting systems being located on one side of the abdomen.

•The estimated incidence is around 1 out of 7,000 births.

•It is more common in males than females with a M:F ratio of 2:1 .

•In crossed renal ectopia, both kidneys are located on the same side and may occur with:

–Fusion (85 %)

–Without fusion (<10 %)

–Extremely rare it can be solitary or bilateral

–The left kidney is three times more likely to migrate to the right than vice versa.

–Other fusion anomalies are extremely rare and include lump kidney, sigmoid kidney, disk kidney and L-shaped kidney.

–There are rare cases of familial crossed ectopia.

•The upper pole of the crossed kidney usually fuses to the lower pole of the normally positioned kidney.

•The kidney usually remains incompletely rotated with the pelvis anterior. However, if complete rotation occurs prior to fusion, an S- or sigmoid kidney results and the pelvices face in opposite directions.

•The lump or disk kidney results from extensive fusion of the developing kidneys.

•In the ‘L’ shaped kidney, the crossed kidney assumes a transverse position.

•The vascular supply of fused kidneys is extremely variable. There may be anomalous branches to both kidneys arising from the aorta or common iliac artery.

•Rarely the renal artery crosses the midline to supply the crossed kidney.

•Urinary drainage is usually by separate ureters entering the bladder on either side of the trigone.

•Most crossed kidneys are asymptomatic and remain undetected throughout life.

•However they may present with infection, a mass or on screening for urinary abnormalities .

•More than 90 % of crossed renal ectopia results in renal fusion.

•Subtypes:

–Type a: inferior crossed fusion

–Type b: sigmoid kidney

–Type c: lump kidney

–Type d: disc kidney

–Type e: L-shaped kidney

–Type f: superiorly crossed fused

•Crossed fused renal ectopia is more common on the left side (Left-to-right ectopy is 3:1).

•In 90 % of crossed ectopy, there is at least partial fusion of the kidneys (the remainder demonstrate two discrete kidneys on the same side, crossed-unfused ectopy).

•In a crossed fused renal ectopic kidney, complications such as nephrolithiasis, infection, and hydronephrosis approaches 50 %.

•Crossed fused renal ectopia usually doesn’t require any primary treatment.

•It is important to diagnose crossed fused renal ectopia prior to any surgical intervention.

•The blood supply to cross-fused kidney is usually anomalous and angiography is recommended before surgical intervention.

•The diagnosis can be confirmed with CT-scan, MRU and isotope scanning.

•There is an increased incidence of associated malformations including cardiac, musculoskeletal, genital, gastrointestinal, anorectal, and renal systems, and occasionally as part of the VACTERL association.

•The most common associated urological abnormality is VUR.

•It has also been described with pelvic malignant lipomatosis and an entire chromosomal translocation involving chromosomes 1 and 6.

•Crossed renal ectopia are usually asymptomatic and require no treatment unless complications develops.

•There is a relatively high incidence of chronic renal disease in crossed renal ectopia, and long term follow up is important.

1.3.10Ectopic Kidney (Figs. 1.19 and 1.20)

•An ectopic kidney results from either incomplete, excess or abnormal ascent of the embryonic kidney.

•Renal ectopia may arise as a result of abnormalities of the ureteric bud or metanephros, an abnormal vascular supply or genetic abnormalities.

•The incidence of renal ectopia in postmortem studies varies from 1 in 500 to 1 in 1,290.

•It occurs slightly more frequently on the left side.

•10 % of cases are bilateral.

•It affects males and females equally.

•It is prone to obstruction and infection.

•Ectopic kidney is also more prone to trauma.

•Around 50 % remain unrecognized throughout life.

•Ectopic kidneys lie outside the renal fossa and may be located in:

–The pelvis

–The iliac fossa

–The chest

–Crossed

•Simple renal ectopia refers to a kidney in the ipsilateral retroperitoneal space and is most commonly located in the pelvis but may be opposite the sacrum or below the aortic bifurcation.