Horseshoe kidney

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Horseshoe kidney is the congenital disorder of kidneys in which the isthmus of both kidneys fuse together during embryonic development leading to appearance of “Horseshoe”. It is the most common fusion defect of kidneys.

Before 1800 A.D. horseshoe kidney regarded as curiosity found only at postmortem examination.However with the advent of the roentgen rays and the intravenous pyelography the diagnostic possibilities to recognize the horseshoe kidney improved, which was later on aided by the ultrasound and computed tomography scan by which horseshoe kidney can be easily diagnosed.^[1]

Horseshoe kidney may be classified into three groups based on:^[2]

1. morphological appearance of fusion,
2. Site of the fusion,
3. Vascular supply or angiographic appearance of the vessels.

Most people with horseshoe kidneys are totally asymptomatic and their kidneys function normally throughout their lives. About quarter of cases are found incidentally, usually during a CT scan due to some other problem. Nonetheless, there are lots of other patients who are predisposed to certain medical sequelae due to the embrogenesis or intrinsic anatomical abnormalities.^[3]

During early fetal development, the kidneys are developed in the pelvis and then later they move upwards in abdomen. Sometimes due to unknown reason the lower ends of both kidneys fuse together forming a ‘U’ shaped single kidney.^[4]

Horseshoe kidney disease must be differentiated from Renal ectopia, Ureteropelvic junction obstruction, Hydronephrosis and Duplicate collecting systems that can be differentiated based on appearances on CT scan.

• Horseshoe kidney is a fairly common condition among other renal fusion abnormalities.Males cases are twice more common than female cases.Although it has been seen in members of same families, but no any particular gene has been found to cause this disease.^[5]

There are no particular gene discovered yet which are directly related to horseshoe kidney but it has been seen associated with other genetic disorders such as Turner syndrome and Edwards syndrome, further suggesting that it is linked to some genes.

There is no particular screening test for horseshoe kidney itself, although CT scanning or renal ultrasonography can be used to screen for the presence of stones, masses, or hydronephrosis.

The majority of patients with horseshoe kidney are asymptomatic and incidentally detected during renal imaging.However the outcome depends on associated urological problems.^[6]

Intravenous pyelography is considered the best initial test.

The majority of patients with horseshoe kidney are asymptomatic.The most common symptoms of horseshoe kidney include abdominal or flank pain,abdominal mass,hematuria and pyuria.

Patients with horseshoe kidney usually appear well and in majority of cases horseshoe kidney is an incidental finding during radiological examination. Physical examination of patients with horseshoe kidney is usually remarkable for abdominal distension, palpable kidney, costovertebral tenderness and palpable bladder.

Urine routine (DR) and urine culture should be done to look for any sign of urinary infection and serum creatinine and electrolytes should be done to check the kidney function.

There are no x-ray findings associated with horseshoe kidney,other than lower renal outline than normal kidneys. However, an x-ray may be helpful in the diagnosis of complications of horseshoe kidney, which include hydronephrosis due to obstruction and renal stones.

Ultrasound may be helpful in the diagnosis of horseshoe kidney.Findings on an ultrasound diagnostic of horseshoe kidney include soft tissue mass,curved configuration or elongation of the lower poles and poorly defined lower poles and lower positioning of upper pole of kidney in abdomen.

CT Scan with contrast is imaging technique of choice. CT Scan of abdomen and pelvis with and without contract is used to look for location of kidneys. It is accurate in determining the anatomical location and also help in differentiating the parenchymal from fibrous isthmus.

MRI is also helpful in diagnosing horseshoe kidney, and is used in conditions where CT Scan is not recommended or available. MRI is also costlier than CT Scan.^[7]

Other imaging studies such as Renal scintigraphy, also known as “renal scans”, can also be used in the diagnosis of horseshoe kidney, by accessing its anatomical structure,renal function and drainage.

There is no treatment required for horseshoe if asymptomatic.The mainstay of therapy is supportive and symptomatic care depending upon the symptoms.

Pharmacologic medical therapy is recommended among patients with Urinary tract infection.

Horseshoe kidney is considered to be asymptomatic and non-fatal renal anomaly that has excellent prognosis in majority of patients without any therapeutic intervention.However in some of the patient medical as well as surgical management required based on the clinical course of the disease.

Although most of the patients doesn’t require surgical intervention but it depends upon the disease process itself and its complications.

There are no established measures for the primary prevention of horseshoe kidney disease.

There are no established measures for the secondary prevention of horseshoe kidney disease.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Before 1800 A.D. horseshoe kidney regarded as curiosity finding only at postmortem examination. However with the advent of the roentgen rays and the intravenous pyelography the diagnostic possibilities to recognize the horseshoe kidney improved, which was later on aided by the ultrasound and computed tomography scan by which horseshoe kidney can be easily diagnosed.

Before 1800 A.D. horseshoe kidney regarded as curiosity found only at postmortem examination.^[1]

• Horseshoe kidney was first documented by Jacopo Berengario da Carpi, a Carpiani Physician, in 1522.
• Horseshoe Kidney was first described and illustrated by Leonardo Botallo, in 1564.
• Later on, Leonard Doldius in Nürnberg in the year 1602 also described the horseshoe kidney during a postmortem examination.
• In 1761, Giovanni Battista Morgagni gave an accurate survey and mentioned cases which had already been published.
• In 1908, diagnosis of horseshoe kidney was first described in Israel by careful Physical Examination.
• Gutierrez introduced the horseshoe kidney pyelographic triangle by using the intravenous pyelogram.^[2]
• Boreham and Gammelgaard, advised aortography as the final diagnosis and as an aid for planning the surgery.
• In 1964, Falor and Rafflo described the value and limitations of aortogram and urography in the association of horseshoe kidney and abdominal aneurysm.

• In 1909, division of the renal isthmus was first done by Martinow, to separate the fused kidney. Later on, details described by Rovsing in 1911, followed by a modification by Papin in 1922.
• In 1940, Foley advised nephropexy in addition to synphsiotomy.
• In 1962, Felton and Miller reported a successful resection of aortic aneurysm associated with the horseshoe kidney stating that there is no hazard in the division of isthmus to gain access.
• In 1933, although Voronoy performed the first human cadaveric kidney transplantation, but the first successful kidney transplantation was performed in Boston by Murray, Merrill and Harrison in 1954.

The following are a few famous cases of horseshoe kidney:^[3]

• Natalie Baitson, a famous singer from Gibraltar.
• Sam Kinison, a popular American comedian,died at the age of 38,found to have horseshoe kidney as per the autopsy report.
• American actor Mel Gibson has a horseshoe kidney.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Horseshoe kidney may be classified into three groups based on: Morphological appearance of fusion, site of the fusion, ans vascular supply or angiographic appearance of the vessels.

According to the morphological appearance of fusion and gross pathology, horseshoe kidney is classified into three types:^[1]

• ‘U’ Shaped, when the lower poles of symmetrically placed kidneys on either sides of vertebral column, fuse together.
• Inverted ‘U’ shaped when upper poles of symmetrically placed kidneys on either sides of vertebral column, fuse together.
• ‘L’ Shaped when one asymmetrical vertically placed kidney fuse with another asymmetrical horizontally placed kidney leading to ‘L’ shape.

Horseshoe kidney can also be be classified into two groups, based on the site of fusion:^[2][3]

• Symmetrical (mid line fusion)
• Asymmetrical (lateral fusion)

Graves described 6 basic patterns of arterial supply in horseshoe kidney, by means of resin cast:^[4][5]

• Type 1: Pattern of blood supply may be similar to that of normal kidney with single artery supplying upper, middle and lower segments.
• Type 2: Upper and middle segments of each kidney may be supplied by a single artery, with a vessel from aorta entering each lower segment.
• Type 3: Sometime the arteries to lower segment arise from aorta by a common trunk.
• Type 4: All three segments are supplied by separate arteries arising from aorta.
• Type 5: The fused segment (isthmus) may also be supplied by arteries which arise above or below the isthmus, these may be unilateral or bilateral and may originate from the aorta independently or by a common trunk.
• Type 6: Finally the fused lower segment may be supplied on one or both sides by branch originating from the common iliac or rarely from hypogastric (internal iliac) or median sacral artery.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Most people with horseshoe kidneys are totally asymptomatic and their kidneys function normally throughout their lives. About quarter of cases are found incidentally, usually during a CT scan due to some other problem. Nonetheless, there are lots of other patients who are predisposed to certain medical sequel due to the embrogenesis or intrinsic anatomical abnormalities.

Most people with horseshoe kidneys are totally asymptomatic and their kidneys function normally throughout their lives. About quarter of cases are found incidentally, usually during a CT scan due to some other problem. Nonetheless, there are lots of other patients who are predisposed to medical sequelae due to the embrogenesis or intrinsic anatomical abnormalities. These issues include:^[1]

• Ureteropelvic junction obstruction : It is the most common problem in horseshoe kidney. It is caused by crossing of ureter over the fused isthmus leading to its obstruction.
• Nephrolithiasis : Stones usually occur when there is obstruction leading to decreased urine output and stasis of urine which create environment for stone formation.
• Recurrent infections : Again due to stasis of urine, because stasis of urine create medium for bacterial growth.
• Hydronephrosis : Basically it is caused by back-flow of urine due to obstruction of ureteropelvic junction.
• Increased incidence of certain cancers such as renal cell carcinoma, Wilm’s tumor and Carcinoid tumors.^[2]

• No genetic determination of horseshoe kidney is known, although it has been seen in identical twins and in siblings within the same family.^[3]

Horseshoe kidney has been seen associated with other genetic disorders such as Turner syndrome,Edwards syndrome and Down’s syndrome.^[4][5]

Grossly, horseshoe kidney is usually fused at the lower of the kidney that is continuous along the mid line anterior to the great vessels. However complete fusion of the kidney produces a mass in the pelvis giving rise to two or more ureters.

On microscopic histopathology analysis, horseshoe kidney is normal unless there is secondary infection or obstructive nephropathy.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

During early fetal development, the kidneys are developed in the pelvis and then later they move upwards in abdomen. Sometimes due to unknown reason the lower ends of both kidneys fuse together forming a ‘U’ shaped single kidney.

Although the exact cause is unknown, but there are two main theories.^[1]

• One theory suggests that during the fifth week of fetal development both kidneys are so close together leading to mechanical fusion of lower end of both kidneys. This kind of fusion creates the fibrous isthmus because it is made of connective tissue.
• Other theory suggests that posterior nephrogenic cells, which are the cells responsible for formation of kidney, migrate to wrong place leading to joining of lower end of both kidneys. This time it is called parenchymal isthmus because it is made of kidney cells.

The horseshoe kidney remains lower in abdomen than normal kidneys due to blockade caused by inferior mesenteric artery during its movement from pelvis to abdomen in 7-8 weeks of development.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Horseshoe kidney disease must be differentiated from renal ectopia, ureteropelvic junction obstruction, hydronephrosis, and duplicate collecting systems that can be differentiated based on appearances on CT scan.

Horseshoe kidney has to be differentiated from the following:^[1]

• Hydro­nephrosis
• Ureteropelvic junction obstruction
• Duplicate collecting systems
• Ovarian cysts
• Renal ectopia
• Crossed fused ectopy
• Pan cake kidney or disc kidney

The main differential diagnosis of HSK is another variety of renal ectopia known as pancake kidney, disc kidney or shield kidney in which there is complete mid-line fusion of the kidneys at the pelvis. It is usually seen below the L2 vertebral body and is frequently associated with vascular abnormalities of the aortic branches.

Hydro­nephrosis
Ureteropelvic junction obstruction
Duplicate collecting systems
Ovarian cysts
Renal ectopia
Crossed fused ectopy
Pan cake kidney or disc kidney

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Horseshoe kidney is a fairly common condition among other renal fusion abnormalities. Males cases are twice more common than female cases. Although it has been seen in members of same families, but no any particular gene has been found to cause this disease.

• The incidence of horseshoe kidney in the population is estimated to be 500 cases per 100,000 births. It is estimated that there was a total 1,600 births based on autopsy data from the 1940s and 1950s.^[1][2]

• Horseshoe kidney is a congenital anomaly result from disruption of the normal embryologic migration of the kidneys.

• There is no racial predilection to horseshoe kidney although it has been reported in identical twins and in sibling within same family.^[3]

• Males are more commonly affected by horseshoe kidney than females.^[4] The male to female ratio is approximately 2 to 1.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

There are no particular gene discovered yet which are directly related to horseshoe kidney but it has been seen associated with other genetic disorders such as Turner syndrome and Edwards syndrome, further suggesting that it is linked to some genes.

• There are no particular gene discovered yet which are directly related to horseshoe kidney but it has been seen associated with other genetic disorders such as Turner syndrome and Edwards syndrome, further suggesting that it is linked to some genes.^[1]

Template:WH Template:WS

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

The majority of patients with horseshoe kidney are asymptomatic and incidentally detected during renal imaging. However the outcome depends on associated urological problems.

• The majority of patients with horseshoe kidney are asymptomatic and incidentally detected during renal imaging. However the outcome depends on associated urological problems.

• Common complications of horseshoe kidney include:^[1]
  • Pelviureteric junction obstruction leading to hydronephrosis
  • Vesicoureteric reflux
  • Renal stones
  • Urinary tract infection
  • Increased risk of nephroblastoma and an approximately threefold to fourfold higher risk for cancer of the renal pelvis^[2]
  • Increased risk for extrarenal disorders that has been associated with horseshoe kidney including:^[3]
    • Gastrointestinal tract malformations
    • Vertebral malformations
    • CNS disorders
    • Cardiovascular disease
  • Increasing association with Wilm’s tumor
  • Blunt traumatic injury as low positioning prevents protection by ribs^[4]

• Prognosis is generally excellent in majority of the patients,without any intervention unless there is an associated complication.^[5][6]

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