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A diagnosis is made in the presence of decreased glomerular filtration rate GFR or if there is analytical most commonly pathological albuminuria , histological or imaging evidence of kidney injury. However, CKD is also associated with an increased risk for premature death and in fact, CKD is projected to become 1 of the top 5 causes of death in the world by and similar trends have been described in individual countries 2 , 3.

Congenital Anomalies of the Kidney and Urinary Tract: A Genetic Disorder?

Congenital abnormalities of the kidney and urinary tract CAKUT include a wide range of abnormalities ranging from asymptomatic ectopic kidneys to life threatening renal agenesis bilateral. Many of them are detected in the antenatal or immediate postnatal with a significant proportion identified in the adult population with varying degree of severity.

CAKUT can be classified on embryological basis in to abnormalities in the renal parenchymal development, aberrant embryonic migration and abnormalities of the collecting system.

Renal parenchymal abnormalities include multi cystic dysplastic kidneys, renal hypoplasia, number agenesis or supernumerary , shape and cystic renal diseases. Aberrant embryonic migration encompasses abnormal location and fusion anomalies. Collecting system abnormalities include duplex kidneys and Pelvi ureteric junction obstruction. Ultrasonography US is typically the first imaging performed as it is easily available, non-invasive and radiation free used both antenatally and postnatally.

Computed tomography CT and magnetic resonance imaging MRI are useful to confirm the ultrasound detected abnormality, detection of complex malformations, demonstration of collecting system and vascular anatomy and more importantly for early detection of complications like renal calculi, infection and malignancies.

Core tip: Congenital abnormalities of the kidney and urinary tract CAKUT are one of the leading causes of end stage renal disease.

They can be classified on embryological basis in to three major categories: 1 abnormalities in the renal parenchymal development; 2 aberrant embryonic migration; and 3 abnormalities of the collecting system. Ultrasonography, computed tomography and magnetic resonance imaging are the primary imaging modalities used in the detection of various CAKUT.

Clinical features vary widely depending on the type, severity and laterality of renal anomaly. Timely diagnosis is crucial in selected anomalies to minimize renal damage, prevent or delay the onset of end stage renal disease ESRD , and provide supportive care to avoid complications of ESRD.

Congenital abnormalities of the kidney and urinary tract occur in per live births and is the leading cause of end-stage renal disease ESRD in children and also cause subsequent renal problems in adulthood like stone formation, infection, hypertension, and renal failure [ 1 ].

Therefore, it is crucial to have early diagnosis and management, whether medical or surgical, to minimize renal damage and to avoid or delay end-stage renal damage. Imaging helps in the early diagnosis, follow-up, surgical planning, detection of complications and associated renal and extra renal malformations.

This review summarizes the various congenital anomalies of kidneys and upper urinary tract, their embryological basis, clinical presentation, imaging features and complications.

The kidneys develop from three structures which succeed each other: The pronephros and the mesonephric and metanephric ducts. Pronephros is the most immature form of kidney and develops from intermediate mesoderm towards the end of 3 rd week of gestation. It is non-functional in human beings and regresses by 4 th week leaving no adult lineage and replaced by mesonephros which later forms the portion of the male and female genital tracts.

The kidneys develop during the 4 th week of gestation by the union of the ureteric bud with the metanephric mass of intermediate mesoderm at the level of the first or second sacral segment. The kidneys initially lie close to each other with the hila directed anteriorly in the pelvis. During 4 th to 8 th weeks of gestation both kidneys gradually ascend to the lumbar region moving further apart from each other and rotate medially almost 90 degrees with the hila now facing anteromedially [ 3 , 4 ].

Congenital anomalies of the kidneys can be classified on embryological basis in to abnormalities in the renal parenchymal development, aberrant embryonic migration and abnormalities of the collecting system [ 5 ]. Renal parenchymal abnormalities include multi cystic dysplastic kidneys MCDK , renal hypoplasia, number agenesis or supernumary , shape and cystic renal diseases.

We have included only upper urinary system anomalies in this review. Many of them like hypoplasia, ectopic kidneys, and anomalies in shape can be asymptomatic and detected incidentally in adults. Others like renal agenesis, MCDK, bilateral PUJO and cystic renal diseases can present early either antenatally with oligohydramnios or later with urinary tract infection, hypertension, proteinuria, renal impairment, abdominal mass, hematuria or stones [ 6 ].

Antenatal screening ultrasonography US allows demonstration of fetal kidneys and urinary bladder from early second trimester and enables to detect a number of major congenital anomalies of the urinary system.

The ultrasound examination of the normal urinary tract consists of the assessment of the presence, location and size of both kidneys and the evaluation of their structure and echogenicity. Evaluation of fetal bladder, external genitalia and the amount of amniotic fluid compliments the examination. Abnormalities detected in antenatal US include hydronephrosis, hydroureter, thickened bladder, cystic kidney, small or dysplastic kidney and absent kidney. Antenatal detection of renal abnormalities warrants postnatal physical examination and postnatal renal ultrasound soon after birth and again at wk of age [ 5 , 7 ].

Cross sectional imaging include computed tomography CT and magnetic resonance imaging MRI help in resolving the complex anatomy, ectopic kidneys not detected on US, duplex collecting system, preoperative evaluation in PUJO and to look for complications like pyelonephritis, renal stones, and malignancies.

Non contrast CT can detect renal stones and nephrocalcinosis. CT urography is useful in duplex system, their complex course, distal opening and associated other genitourinary malformations. MRI has the advantages of lack of ionizing radiation, better soft tissue contrast and detection of collecting system abnormalities even without contrast [ 8 ]. Disadvantage is requirement of sedation in small children, cost and availability [ 3 , 9 , 10 ]. Renal agenesis: Complete absence of one or both kidneys indicates renal agenesis.

It thought to result from a lack of induction of the metanephric blastema by the ureteral bud. Bilateral agenesis is incompatible with life and is associated with pulmonary hypoplasia and limb defects.

It is often asymptomatic and compensatory hypertrophy in other kidney may cause glomerulosclerosis in adults. Unilateral renal agenesis is often incidentally detected in adults in US or CT performed for other reasons. Associated abnormalities can be seen like ipsilateral seminal vesicle cyst, ipsilateral absence of seminal vesicle or mullerian abnormalities [ 12 , 13 ] Figures 1 and 2.

Supernumary kidneys: A supernumerary kidney is an uncommon urogenital anomaly with less than cases reported in the literature. In this one or more accessory kidneys are seen often on the left and caudal to the native kidney. Mostly the accessory kidney is smaller in size with reduced function. US is useful in the morphological characterisation while the rest aid in functional assessment.

Supernumary kidneys commonly have associated various urogenital and non urogenital anomalies [ 14 , 15 ]. Persistent fetal lobulations: Persistent fetal lobulations is a normal variant seen in adult kidneys due to incomplete fusion of the developing renal lobules and could be mistaken for renal scarring. However it is seen as smooth indentation of the renal outline in-between the pyramids on ultrasonogram USG , CT OR MRI as compared to renal scarring where indentation is not smooth, asymmetrical and it overlies the renal pyramids [ 16 ] Figure 3.

Hypertrophied column of bertini: It is the extension of renal cortical tissue which separates the pyramids towards the central parenchyma. It is important as it can be mistaken for a renal mass on US. It is usually located in the mid portion of the left kidney. Key to correct identification is the fact that it is in continuity with, and have signature of normal renal parenchyma regardless of the type of imaging modality, CT or MRI [ 17 , 18 ] Figures 3 - 5.

Dromedary hump: Normal variant of renal contour appearing as focal contour bulge, caused by the splenic impression onto the superolateral left kidney. Another clue is calyces underlying the hump extend further laterally into the hump than the other calyces [ 16 ] Figure 3. Renal hilar lip: A renal hilar lip is an infolding of the cortex at the level of the renal sinus giving a pseudo mass appearance. Again cortical signature and careful evaluation of contiguous images on CT or MRI help in resolving the confusion [ 19 ].

Junctional parenchymal defect: It is a normal variant seen as a triangular echogenic area due to the extension of sinus fat into the cortex. It results from embryonic fusion of renunculi. It can be distinguished from small angiomyolipoma AML or scar by its continuity with renal sinus fat and its typical location in interpolar region [ 16 , 17 ].

It is often unilateral and can have normal or mildly reduced function. It can be global or segmental. Global hypoplasia needs to be differentiated from atrophic kidneys due to pyelonephritis or chronic vascular diseases in adults.

Small smooth kidney from chronic vascular diseases are difficult to differentiate from hypoplasia [ 4 ]. Segmental renal hypoplasia also known as Ask-Upmark kidney is a cause of secondary hypertension in young adults. Imaging reveals small nonfunctioning kidney or focal hypoplasia of upper or lower pole and final diagnosis is made on characteristic histological features [ 4 , 5 , 20 ] Figures 6 and 7. MCDK is a developmental disorder of the kidney, in which the normal renal parenchyma is replaced by multiple, non-communicating cysts of varying size with poorly identified echogenic parenchyma and atretic upper ureters.

USG antenatal or postnatal is diagnostic and should be differentiated from hydronephrosis which have communicating cysts [ 7 ]. Polycystic kidney disease presenting in adults shows multiple non communicating cysts similar to MCDK. However adult age of onset, bilateralism, enlarged kidney, intervening normal renal parenchyma and positive family history are helpful in differentiating from MCDK [ 22 ].

DMSA can be performed to establish non functioning kidney Figure 8. The natural course in utero is variable and the final result is a non-functional kidney [ 23 ]. Congenital renal anomalies in the position and in the renal fusion are the result of impaired cephalic migration from the pelvis to the flank of the ureteric bud and metanephric blastema. This process of ascent begins in 5 th week and ends at 9 th week of gestation.

It includes both ectopic location of kidneys and abnormal fusion of whole or part of the kidneys. Renal ectopia is a congenital renal anomaly characterized by abnormal location of kidneys outside the flank region L1-L3 vertebral levels. It can be simple ectopia where ectopic kidney is located on the same as its ureter or crossed ectopia when it is located on the opposite from its ureteric orifice.

Both can be unilateral or bilateral. The location, in order of frequency, may be pelvic, iliac, abdominal or chest. Ectopic kidney is usually smaller with varying degree of malrotation. The ureter has a length according to the location of the kidney and blood supply is from iliac or infrarenal abdominal aorta with typically multiple arteries. USG is diagnostic in most of the cases and cross sectional imaging or nuclear medicine studies are needed when USG visualized is suboptimal due to bowel gas, small kidneys or intrathoracic location [ 25 ].

Crossed renal ectopia is seen in and often incidentally detected. Commonest fusion pattern is fusion of lower pole of orthotopic kidney to the upper pole of crossed ectopic kidney. Other described patterns include sigmoid, L shaped, discoid and cake kidneys. USG shows absent kidney on one side and careful evaluation often reveals it on the opposite lumbar or iliac region.

Often there is associated other genitourinary malformations and ectopic kidneys are complicated by stones, infection or hypertension from multiple anomalous arteries [ 3 ]. CT urography is helpful in confirming the diagnosis and demonstration of collecting system, arterial supply and complications. Ectopic kidneys need to be differentiated from renal transplants, nephroptosis, surgical repositioning of kidneys and nephrectomy Figures 9 - Horseshoe kidney is the most common congenital anomaly seen in 1 in adults [ 27 ].

It is formed by fusion across the midline of two distinct functioning kidneys, one on each side of the midline. They are connected by an isthmus of functioning renal parenchyma or fibrous tissue. In the remainder the superior or both the superior or inferior poles are fused.

It is due to normal ascent of kidneys impaired by inferior mesenteric artery which hooks over the isthmus resulting in a lower abdominal location and abnormal rotation, especially at the lower poles Figure The pelvis and ureters are anterior, ventrally crossing the isthmus [ 3 ]. Horse shoe kidney is prone to numerous complications due to its location and poor drainage like hydronephrosis, secondary to pelviureteric junction obstruction, renal calculus, infection, increased incidence of malignancy Wilms tumour, transitional cell carcinoma, carcinoid and possibly renal cell carcinoma [ 28 ] and increased susceptibility to trauma.

On USG, clue to diagnosis is poor visualization of bilateral lower pole which should alert the sonographer to look for abnormal tissue anterior to aorta representing the isthmus.

Congenital Disorders of the Human Urinary Tract: Recent Insights From Genetic and Molecular Studies

Congenital abnormalities of the kidney and urinary tract CAKUT include a wide range of abnormalities ranging from asymptomatic ectopic kidneys to life threatening renal agenesis bilateral. Many of them are detected in the antenatal or immediate postnatal with a significant proportion identified in the adult population with varying degree of severity. CAKUT can be classified on embryological basis in to abnormalities in the renal parenchymal development, aberrant embryonic migration and abnormalities of the collecting system. Renal parenchymal abnormalities include multi cystic dysplastic kidneys, renal hypoplasia, number agenesis or supernumerary , shape and cystic renal diseases. Aberrant embryonic migration encompasses abnormal location and fusion anomalies.

Congenital Anomalies of the Kidney and Urinary Tract

Kirsten Y. Renkema, Paul J. Winyard, Ilya N. Knoers, Ernie M.

The purpose of this review is not only to describe the congenital renal anomalies, but also to analyze the more recent therapeutic interventions that may modify the natural history of some of these severe conditions. Enid Gilbert-Barness is an extremely distinguished and well-known pediatric pathologist that has educated generations of medical students, residents, and fellows, written numerous books, chapters, and articles in the field of embryo-fetal and pediatric pathology during her long career and is now relinquishing her position as the Editor-in-Chief of Fetal and Pediatric Pathology. I am very humbled to accept the invitation by the publisher to contribute a manuscript to the festschrift in her honor. If one tries to define Dr.

Congenital Anomalies of the Kidney and Urinary Tract: A Genetic Disorder?

Review ARTICLE

The urinary tract comprises the renal pelvis, the ureter, the urinary bladder, and the urethra. The tract acts as a functional unit, first propelling urine from the kidney to the bladder, then storing it at low pressure inside the bladder which intermittently and completely voids urine through the urethra. Congenital diseases of these structures can lead to a range of diseases sometimes associated with fetal losses or kidney failure in childhood and later in life. In some of these disorders, parts of the urinary tract are severely malformed. In other cases, the organs appear grossly intact yet they have functional deficits that compromise health. Human studies are beginning to indicate monogenic causes for some of these diseases.

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    Editor-in-Chief of Fetal and Pediatric Pathology. I am very humbled to accept the invitation by the publisher to contribute a. manuscript to the.

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