Renal ectopia

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

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

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Pelvic kidney is the most common example of renal ectopia. Other sites of ectopic kidneys include the iliac region, the abdomen, the chest, and, in some cases, the contralateral side, referred to as “crossed” renal ectopia.

There are six subtypes of crossed fused renal ectopia:

• Inferior ectopia type with upper pole of ectopic kidney fusing with lower pole of normal kidney.
• Sigmoid or S-shaped kidney where hilum of ectopic kidney faces laterally and that of normal kidney medially and with fusion form S-shaped mass.
• Lump kidney with fusion of two kidneys over a wide margin with ureter from ectopic kidney crossing the midline.
• L-shaped or Tandem kidney in which the ectopic kidney is placed horizontally fusing with lower pole of normal kidney.
• Disc kidney with extensive fusion of two kidneys forming a disc shaped mass.
• Superior ectopia type with ectopic kidney placed above the normal kidney and fusing with its upper pole.

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

The exact pathogenesis of [disease name] is not fully understood.

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The pathophysiology of [disease/malignancy] depends on the histological subtype.

• Normal ascent of the kidneys is required for formation of the extraperitoneal perirenal fascial planes.
• Ectopia (or renal agenesis) results in failure of development of fascial layers in the flanks on the side not occupied by renal tissue.
• Lack of restraining fascia leads to possible malposition of bowel into the extraperitoneal fat of the empty renal fossa and relaxation of mesenteric supports for bowel loops in this region.

The normal physiology of [name of process] can be understood as follows:

• Crossed ectopy = kidney located on the opposite side of the midline from its ureter. ^{[1] [2] [3] [4]}
• 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)
• Due to improper renal ascent in embryogenesis (4^th-8^th week of fetal life – normally, the kidney reaches its appropriate position at L2 level at the end of the 2^nd month)
• Fusion of the kidneys within the pelvis leads to crossed-fused renal ectopia.
• 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.

• Renal ectopia results as a consequence of abnormal renal ascent in embryogenesis with fusion of the kidneys within the pelvis.
• It is thought to occur in the first trimester, at around 4th-8th week of fetal life (In a normal situation the kidney reaches its appropriate position at L2 level at the end of the 2nd month).
• 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.
• Normal ascent of the kidneys is required for formation of the extraperitoneal peri-renal fascial planes and therefore ectopia results in failure of development of fascial layers in the flanks on the side not occupied by renal tissue. The lack of restraining fascia leads to possible malposition of bowel into the extra-peritoneal fat of the empty renal fossa and relaxation of mesenteric supports for bowel loops in this region.

[Disease name] is transmitted in [mode of genetic transmission] pattern.

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Genes involved in the pathogenesis of [disease name] include:

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• [Gene3]

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The development of [disease name] is the result of multiple genetic mutations such as:

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On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

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

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Common causes of [disease] include [cause1], [cause2], and [cause3].

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Ectopic kidney occurs during fetal development. Kidneys, in general, develop as outgrowths or buds within the pelvis before they move upwards to their position at the rear end of the rib cage. The upward movement of the kidney occurs between the 6th and 9th weeks of embryo development. ‘Ectopic’ usually refers to an organ that is out of place. When one of the kidneys remains in the pelvis, or moves upward but fuses with the second kidney, or moves higher than its normal position, an ectopic kidney is formed. Some of the causes for this defect in movement are:

• Genetic defects

• Defects in the kidney tissue that provides the signal to move upward from the pelvis

• Exposure of the pregnant mother to a drug, or a chemical, or an illness that results in defects in kidney development in the baby

• Under-developed kidney bud

The precise mechanism of development of renal fusion anomalies is not fully understood and several theories have been put forward to explain the anomaly :

• The Mechanical Theory proposes that during cephalad migration, the kidneys pass through the fork between the two umbilical arteries and any positional change in these arteries squeeze the kidneys close together allowing their fusion. Fusion of both nephrogenic blastemas with early arrested migration result in completely fused pelvic kidney. Abnormal position of an umbilical artery can result in abnormal migration of a renal unit to the contralateral side following the path of least resistance (crossed renal ectopia).
• The Theory of Abnormal Caudal Rotation proposes that fusion occurs due to lateral flexion and rotation of the caudal end of the embryo disturbing the relative position of the nephrogenic blastema and ureteric bud. The distal curled end of the vertebral column permit one ureter to cross the midline and enter the opposite nephrogenic blastema or transplant the kidney and ureter to the opposite side during ascent. Association of scoliosis with crossed renal ectopia supports this theory.
• The Ureteral Theory states that cross over is strictly a ureteral phenomenon with the developing ureteral bud wandering to the opposite side and inducing the differentiation of the contralateral metanephric blastema and it is assumed that the metanephric tissue that does not receive a ureteric bud regresses.
• The Teratogenic Theory suggest that renal ectopia results from abnormal migration of posterior nephrogenic cells due to teratogenic insult forming a parenchymal isthmus. The increased incidence of malignancies and other organ system anomalies associated with renal ectopia possibly supports this theory.
• The Genetic Theory suggests that genetic influence may play a role because some renal fusion anomalies have been reported to occur in identical twins and siblings within the same family. It is suggested that the sonic hedgehog gene signal is critical for kidney positioning along the mediolateral axis and its disruption will result in renal fusion.

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• [Cause1]
• [Cause2]
• [Cause3]

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Less common causes of [disease name] include:

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List the causes of the disease in alphabetical order:

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

[Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as [differential dx1], [differential dx2], and [differential dx3].

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[Disease name] must be differentiated from [[differential dx1], [differential dx2], and [differential dx3].

Renal ectopia has to be differentiated from the following:

• Hydro­nephrosis
• Ureteropelvic junction obstruction
• Duplicate collecting systems, ovarian cysts
• Mesenteric cysts
• Sacrococcygeal teratoma.

[Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as [differential dx1], [differential dx2], and [differential dx3].

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[Disease name] must be differentiated from [differential dx1], [differential dx2], and [differential dx3].

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As [disease name] manifests in a variety of clinical forms, differentiation must be established in accordance with the particular subtype. [Subtype name 1] must be differentiated from other diseases that cause [clinical feature 1], such as [differential dx1] and [differential dx2]. In contrast, [subtype name 2] must be differentiated from other diseases that cause [clinical feature 2], such as [differential dx3] and [differential dx4].

On the basis [symptom 1], [symptom 2], and [symptom 3], [disease name] must be differentiated from [disease 1], [disease 2], [disease 3], [disease 4], [disease 5], and [disease 6].

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

• Horseshoe kidney is the most common renal fusion anomaly which combines three anatomical abnormalities: ectopia, malrotation and vascular changes and is found more commonly in men than in women with a ratio of 2:1. It accounts for 90% of all fusion anomalies and occurs in about 0.25 % of the population. An incidence of 1 in 666 cases was found after analyzing radiological data of 15320 patients at a single institution. It is estimated the prevalence rates for HSK in adults examined by sonography as 1:708 and by CT as 1:474. In a cross sectional study on 12000 patients using sonography and contrast urography, only 4 cases (0.03%) of HSK was found. In contrast, a sonographic study from Nepal has reported an incidence of 1 in 516 (61 HSKs out of 31498 patients screened, 0.2%) with male to female ratio of 1:2 (20 males; 41 females). We have reported an incidence of 1 in 97 cases (7 out of 682 cases; 1.02%) after retrospective analysis of multidetector CT scans of 682 patients . Natsis et al has reported an incidental finding of HSK in 1 male out of 250 (0.4%) Greek cadavers dissected during a period of 30 years. Though it is suggested that there is no racial determination for HSK, available literature indicates that the incidence of horseshoe kidney varies in different populations and further research is needed to throw some light on this aspect.

• Crossed renal ectopia is a rare type of anomaly in which both the kidneys are situated on one side and in about 90% of such cases the crossed ectopic kidney is fused with the orthotopically located kidney. Crossed fused renal ectopia (CFRE) is the second most common renal fusion anomaly with an estimated incidence of 1:1300 to 1:7500 [1,2]. It is both a fusion and ectopic anomaly and occurs in about 0.08% – 0.01% cases. The prevalence of the crossed renal ectopia with fusion was estimated to be 1 in 1000 live births [34]. In a review of 400 children evaluated by DMSA renal scan, crossed fused renal ectopia was found in 7 cases (1.75%). In another retrospective review, the incidence of CRE was reported as 1 out of 3078 CT scans. We have reported 3 cases of CFRE (2 females, 1 male) in a retrospective analysis of MDCT scans of 682 patients with an estimated incidence of 0.43%. The true incidence of this anomaly is not known because a large majority of the patients having this anomaly remain asymptomatic and undetected. The left kidney is most commonly ectopic crossing to the right side of the abdomen and the condition is more common in males.

• The incidence/prevalence of [disease name] is approximately [number range] per 100,000 individuals worldwide.
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• There is no racial predilection to [disease name].
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• 2:1 male to female ratio

• A single renal mass with two collecting systems is located on one side of the abdomen.
• Left-to-right ectopy three times more common.

• The majority of [disease name] cases are reported in [geographical region].

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

There are no established risk factors for [disease name].

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The most potent risk factor in the development of [disease name] is [risk factor 1]. Other risk factors include [risk factor 2], [risk factor 3], and [risk factor 4].

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Common risk factors in the development of [disease name] include [risk factor 1], [risk factor 2], [risk factor 3], and [risk factor 4].

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Common risk factors in the development of [disease name] may be occupational, environmental, genetic, and viral.

There are no established risk factors for [disease name].

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The most potent risk factor in the development of [disease name] is [risk factor 1]. Other risk factors include [risk factor 2], [risk factor 3], and [risk factor 4].

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Common risk factors in the development of [disease name] include [risk factor 1], [risk factor 2], [risk factor 3], and [risk factor 4].

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  • [Risk factor 2]
  • [Risk factor 3]

• Less common risk factors in the development of [disease name] include:
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

There is insufficient evidence to recommend routine screening for [disease/malignancy].

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According to the [guideline name], screening for [disease name] is not recommended.

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According to the [guideline name], screening for [disease name] by [test 1] is recommended every [duration] among patients with [condition 1], [condition 2], and [condition 3].

Prenatal sonography can detect ectopic kidneys in the first trimester of the pregnancy. Timely diagnosis allows for regular monitoring and helps to prevent complications such as hypertension and renal failure.

There is insufficient evidence to recommend routine screening for [disease/malignancy].

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According to the [guideline name], screening for [disease name] is not recommended.

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According to the [guideline name], screening for [disease name] by [test 1] is recommended every [duration] among patients with:

• [Condition 1]
• [Condition 2]
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

If left untreated, [#]% of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].

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Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].

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Prognosis is generally excellent/good/poor, and the 1/5/10-year mortality/survival rate of patients with [disease name] is approximately [#]%.

• The symptoms of (disease name) usually develop in the first/ second/ third decade of life, and start with symptoms such as ___.
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Renal Ectopia may be associated with the following abnormalities :

• Contralateral renal agenesis
• Bilateral ectopia
• Genital anomalies such as bicornuate or unicornuate uterus
• Absent uterus
• Duplicate or rudimentary vagina
• Undescended testes
• Hypospadias
• Duplicate urethra
• Rarely adrenal anomalies.
• Cardiac and skeletal anomalies are more common

• Prognosis is generally excellent/good/poor, and the 1/5/10-year mortality/survival rate of patients with [disease name] is approximately [–]%.
• Depending on the extent of the [tumor/disease progression] at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as poor/good/excellent.
• The presence of [characteristic of disease] is associated with a particularly [good/poor] prognosis among patients with [disease/malignancy].
• [Subtype of disease/malignancy] is associated with the most favorable prognosis.
• The prognosis varies with the [characteristic] of tumor; [subtype of disease/malignancy] have the most favorable prognosis.

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