An ectopic kidney is a

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

that is not located in its usual position ( ectopia) in the lumbar retroperitoneal space. It is the result of anomalous migration of the kidneys from their origin in the fetal pelvis during embryogenesis. The diagnosis is usually made during antenatal and/or postnatal testing, when the ectopic kidney is found incidentally. Although most patients with renal ectopia are asymptomatic, some can develop symptoms due to complications such as

kidney stones Kidney stone disease (known as nephrolithiasis, renal calculus disease, or urolithiasis) is a crystallopathy and occurs when there are too many minerals in the urine and not enough liquid or hydration. This imbalance causes tiny pieces of cr ...

urinary tract infections A urinary tract infection (UTI) is an infection that affects a part of the urinary tract. Lower urinary tract infections may involve the bladder (cystitis) or urethra ( urethritis) while upper urinary tract infections affect the kidney (pye ...

and

hydronephrosis Hydronephrosis is the hydrostatic dilation of the renal pelvis and Renal calyx, calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the ureter, and hydronephroureter describes the dila ...

Embryology

The kidney arises from the intermediate

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...

and has three embryological forms:

pronephros Pronephros is the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development. It is succeeded by the mesonephros, which in fish and amphibians remains as the adult kidney. In am ...

mesonephros The mesonephros () is one of three excretory system, excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is included ...

and

metanephros Kidney development, or nephrogenesis, describes the embryologic origins of the kidney, a major organ in the urinary system. This article covers a 3 part developmental process that is observed in most reptiles, birds and mammals, including humans. ...

. The pronephros and mesonephros are the primitive transient stages, while the metanephros is the final and functional stage that later forms the permanent kidneys. The metanephros is formed at around fifth to sixth week of gestation and is composed of the metanephric mesenchyme (the proper kidney) and the

ureteric bud The ureteric bud, also known as the metanephric diverticulum, is a protrusion from the mesonephric duct during the development of the urinary and reproductive organs. It later develops into a conduit for urine drainage from the kidneys, which, in c ...

(collecting system and ureter). This metanephric unit then ascends from the pelvis into the retroperitoneal renal fossa while simultaneously rotating 90° so that the developing kidney is positioned vertically with the hilum pointing medially. This whole process of renal ascent and rotation is generally completed by the eighth to ninth week of gestation. When the mature kidney fails to ascend to its normal location in the retroperitoneal space between T12 to L3 vertebral levels, it is called an ectopic kidney. Numerous factors have been hypothesized to affect the proper ascent and rotation of the kidneys, including genetic factors, developmental defects in the metanephric tissue and the ureteric bud, teratogens and maternal illnesses and exposures during pregnancy.

Classification

An ectopic kidney can be classified based on its location in the corresponding cavity, whether it is simple or crossed and whether there is associated fusion with the ipsilateral kidney. The types of ectopic kidney include: * Simple: kidney that remains on the same side of the body but in an abnormal location. * Crossed: kidney that crosses the midline so that it's on the opposite side of the body. It can be with or without fusion to the ipsilateral kidney. * Cephalad: kidney that ascends until its reaches the level of T10 vertebra, just below the diaphragm. This type is usually associated with omphaloceles and other abdominal wall defects. Pelvic-ectopic-kidney-with-English-labels

Pelvic-ectopic-kidney-with-English-labels

* Thoracic: kidney that protrudes through the diaphragm into the

posterior mediastinum Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to anterior ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that ...

. An intrathoracic kidney could be a "real" ectopic kidney without any diaphragm abnormalities or can be related to

diaphragmatic hernias The thoracic diaphragm, or simply the diaphragm (; ), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the most important muscle of respiration, and separa ...

or traumatic diaphragm ruptures. * Pelvic: kidney that fails to ascend and remains in the

pelvic brim The pelvic brim is the edge of the pelvic inlet. It is an approximately butterfly-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis. Structure The pelvic ...

, below the level of aortic bifurcation. * Abdominal: kidney that is anywhere between its origin in the pelvis and its normal position in the renal fossa.

Incidence

Data on the incidence of ectopic kidneys is inconsistent since renal ectopia may be diagnosed antenatally, but it also may be asymptomatic and found only incidentally or postmortem. Average incidence is about 1 in 900 in autopsy studies and 1 in 3000 in imaging studies. The incidence also varies depending on the type of ectopy. For example, pelvic kidneys are seen in 1 per 2000 to 1 per 3000 cases and are generally more common than cephalad and intrathoracic kidneys which only occur in 1 per 22,000 cases.

Characteristics

Rotation

Since kidney ascension and rotation occur simultaneously, a faulty ascension generally results in an incomplete rotation so that the hilum is facing anteriorly instead of medially. The axis of the ectopic kidney may be vertical, medial or horizontal depending on how far up it has ascended.

Shape

The shape of the ectopic kidney can vary depending on its location and the nearby structures. It could retain its normal bean shape, or it can be irregular, lobulated, underdeveloped, or even dysplastic.

Blood supply

The vascular supply is usually anomalous and it varies depending on where ascension is halted.

Renal arteries The renal arteries are paired arteries that supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle. The renal arteries carry a large portion of total blood flow to the kidneys. Up to a ...

may originate from the distal aorta, the aortic bifurcation, the iliac arteries or the inferior mesenteric artery.

Ureter

The

ureter The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In an adult human, the ureters typically measure 20 to 30 centimeters in length and about 3 to 4 millimeters in diameter. They are lin ...

of an ectopic kidney inserts normally into the bladder on the ipsilateral side, except when there is an associated

ectopic ureter Ectopic ureter (or ureteral ectopia) is a medical condition where the ureter, rather than terminating at the urinary bladder, terminates at a different site. In males this site is usually the urethra, in females this is usually the urethra or vag ...

, which is rare. The ureter can also be longer (such as in cephalad and thoracic kidneys) or shorter (such as in pelvic kidneys) to accommodate for the distance traveled.

Adrenal gland

The

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer adrenal corte ...

undergoes embryological development separate from that of the kidney, and so it retains its normal location in the retroperitoneal renal fossa even with the presence of an ectopic kidney.

Associated conditions

Ectopic kidneys are commonly associated with genital anomalies such as

hypospadias Hypospadias is a common malformation in fetal development of the penis in which the urethra does not open from its usual location on the head of the penis. It is the second-most common birth defect of the male reproductive system, affecting about ...

and

cryptorchidism Cryptorchidism, also known as undescended testis, is the failure of one or both testes to descend into the scrotum. The word is . It is the most common birth defect of the male genital tract. About 3% of full-term and 30% of premature infant boy ...

in males and vaginal or uterine agenesis, unicornuate,

bicornuate A bicornuate uterus or bicornate uterus (from the Latin ''cornū'', meaning "horn"), is a type of Müllerian anomaly in the human uterus, where there is a deep indentation at the fundus (top) of the uterus. Pathophysiology A bicornuate uterus ...

septate In biology, a septum (Latin for ''something that encloses''; septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatrial se ...

uterus in females. Other non-urogenital anomalies can also be present and they usually involve cardiac and skeletal structures. Renal ectopia is also sometimes part of a congenital syndrome.

Diagnosis

An ectopic kidney is often diagnosed antenatally when ultrasonography reveals an empty renal fossa with a normal amniotic fluid volume, which should prompt search for the kidney in other locations. However, if renal ectopia is not diagnosed in the antenatal or postnatal periods, it may remain asymptomatic and be diagnosed incidentally. It can also result in complications such as urinary tract infections (UTIs), kidney stones,

vesicoureteral reflux Vesicoureteral reflux (VUR), also known as vesicoureteric reflux, is a condition in which urine flows retrograde, or backward, from the urinary bladder, bladder into one or both ureters and then to the renal calyx or kidneys. Urine normally trave ...

(VUR), or

which would lead to the diagnosis of an ectopic kidney. Symptoms related to these complications include abdominal pain, palpable mass,

urinary incontinence Urinary incontinence (UI), also known as involuntary urination, is any uncontrolled leakage of urine. It is a common and distressing problem, which may have a significant effect on quality of life. Urinary incontinence is common in older women ...

, fever and

hematuria Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. "Gross hematuria" occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable with ...

Evaluation

Initial evaluation for ectopic kidneys generally includes the following elements: * A physical exam to check for obvious urogenital and non-urogenital deformities. * Blood tests such as serum creatinine to assess the kidney function. * Urinalysis to check for associated complications. * Imaging studies such as

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

, voiding cystourethrograms, radionuclide scans, or

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

to assess location, size, shape and/or function of the kidney.

Management and Prognosis

Although limited, studies on children with ectopic kidneys show no adverse effects on blood pressure and kidney function during childhood follow-up visits. Nonetheless, it is recommended to periodically monitor patients from the time of diagnosis until adolescence. Follow-up visits are generally every 2 years and they include a kidney ultrasound, a blood pressure measurement, serum creatinine and a urinalysis to assess kidney function and screen for complications. During adulthood, an annual blood pressure check and urinalysis are sufficient, unless symptoms or complications arise.

References

External links

Nephrology Congenital disorders of urinary system Kidney anatomy {{genitourinary-stub