Congenital Anomalies of the Kidney and the Urinary Tract (CAKUT)

Abstract

This article reviews the majority of Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) with emphasis in Pediatric Pathology describing and illustrating lesions as varied as ureteral duplications, ureteropelvic junction obstruction, horseshoe kidney, posterior urethral valve and prune belly syndrome, obstructive renal dysplasia, nonmotile ciliopathies and several syndromes associated with renal malformations (Meckel-Joubert, short rib, Bardet-Biedl, asplenia/polysplenia, hereditary renal adysplasia, Zellweger, trisomies, VACTER-L, Potter, caudal dysplasia, and sirenomelia), as well as ADPK, and ARPK. 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.

Figure 1.

The nephrectomy was performed because of a Wilms tumor. However, the kidney had a double ureter.

Figure 2.

The ureteropelvic junction (UPJ) was probed after stretching the kink in the lumen and it was patent, but stenotic. The patient had been symptomatic for years and required surgery.

Figure 3.

(A) After urine was drained from the urinary bladder (UB), the neonate’s skin wrinkled like a prune. Observe the small chest in contrast to the large abdomen. The pulmonary hypoplasia is secondary to a combination of elevated diaphragm and oligohydramnios. (B) Both kidneys are multicystic and dysplastic, the ureters are tortuous and dilated and the UB is thick and dilated. (C) The kidneys were bivalved and were hydronephrotic. (D) The urinary bladder demonstrates posterior urethral valves.

Figure 4.

Composite photograph of obstructive renal dysplasia with hydronephrosis. (A) Both kidneys were dissected with the ureters still attached to the UB and then bivalved to demonstrate the hydronephrosis. (B) Whole-mounted section from the kidney was stained with H&E. The cortex is relatively well preserved while the medulla is more compressed by the hydrostatic pressure of the urine in the renal pelvis. (C) Close-up view of the kidney affected by hydronephrosis. (D) Whole-mounted section from the kidney was stained with trichrome. Observe the better preserved renal cortex compared to the fibrotic medulla in blue.

Figure 5.

Gross and photomicrographs from nonobstructive renal dysplasia. (A) The kidneys were left attached to the aorta by the renal arteries. The ureters are of normal caliber. The UB is small because the kidneys were producing a very small amount of urine. (B) H&E-stained whole-mounted section from the kidney. The parenchyma is disorganized and there are numerous cysts surrounded by concentric fibrosis. (C) Trichrome-stained whole-mounted section from the kidney. There is extensive fibrosis throughout this kidney (stained in blue).

Figure 6.

Composite photograph of a patient with Meckel syndrome. (A)Posterior view of a child with an occipital encephalocele. The ears are low set. (B)Both kidneys are dysplastic and the ureters as well as the urinary bladder are small as seen in syndromic (nonobstructive) renal dysplasia. (C) Cut section throughout the liver demonstrates areas of fibrosis mainly at the right lobe. Histologically, the liver disclosed congenital hepatic fibrosis. (D) Polydactyly of both feet. The hands were normal.

Figure 7.

Newborn with Joubert syndrome. (A) The neonate had a parrot-beak nose, slightly low-set ears, a distended abdomen and bilateral post-axial polydactyly. (B) The cerebellar vermis was absent. (C) Both feet also demonstrated postaxial polydactyly. (D) The kidneys lost their reniform shape, were large and contained multiple round cysts.

Figure 8.

Newborn with short-rib syndrome who died during the first day of life due to respiratory insufficiency. (A) The baby had a large cranium with large fontanelles, a median cleft lip and palate, bilateral anophthalmia, a very small thorax and a protuberant abdomen. (B) The left kidney weighed less than half the weight of the right and both had cystic renal dysplasia. (C) The renal parenchyma is disorganized with concentric fibrosis around two dilated tubules. There is a single glomerulus in the photo next to a large, cystically-dilated space to the left. (D) Antero-posterior and lateral X-rays demonstrate large cranium, short ribs, hypoplastic ilia, and short, symmetrical extremities.

Figure 9.

Nonobstructive renal dysplasia-polysplenia syndrome. (A) The only apparent body anomaly was a distended abdomen, but the child did not have a hypoplastic thorax. (B) There were several small splenicula at the left upper quadrant. The liver was moved up to allow better visualization and the forceps are holding the splenicula. (C) Both kidneys were dysplastic; however, the ureters were of normal caliber and the renal pelvis was not dilated. (D) Close-up view from the left kidney discloses lack of demarcation between cortex and medulla and several small cysts scattered throughout the parenchyma.

Figure 10.

Photomicrographs from kidneys, liver and pancreas from the same patient shown in figure 9. (A) H&E-stained kidney section with 10× lens, original magnification. Notice two islands of cartilage at the left upper corner (arrow). There is total architectural disorganization and multiple tubules are dilated. (B) H&E-stained liver section with 10× lens, original magnification. The portal triad contains an expanded portal plate with numerous dilated bile ducts toward the periphery of the plate. The histology is diagnostic of a portal plate malformation. (C) Trichrome-stained liver section with 10× lens, original magnification. Notice the blue staining of the portal plate, the vein at the center and also numerous dilated, irregular bile ducts at the periphery. (D) Pancreatic cystic dysplasia (H&E-stained section, 2.5× lens). The changes were focal with areas of normal histology and other parts containing cystic ducts. The photomicrograph was taken at the transition between normal and dysplastic pancreas.

Figure 11.

Fetus with trisomy 13, holoprosencephaly, and renal dysplasia. (A) Cranial bases from two fetuses: to the left the fetus with trisomy 13, holoprosencephaly, and arhinencephaly; to the right a fetus aborted because of trisomy 21. To the left, there is absence of crista galli (arrow). Compare with the fetus to the right that has a normal crista galli. (B) H&E-stained section from the fetal retina (10× lens) demonstrates the presence of cartilage and multiple neuronal rosettes diagnostic of retinal dysplasia (arrows). (C) H&E-stained renal section with 2× lens, original magnification. There are numerous dilated tubules at the corticomedullary junction and three nodules of dysplastic renal parenchyma in the medulla. (D) A small nodule was noticed in the spleen that was sampled and histologically was a splenopancreatic fusion (H&E-stained section from the spleen,10× lens).

Figure 12.

Renal anomalies in trisomy 18. (A) Neonate with trisomy 18 and overlapping of the fingers associated with fingernail hypoplasia. (B) Kidneys from the same patient with nonobstructive renal dysplasia. (C) H&E-stained renal section with 2× lens, original magnification. Observe a small island of cartilage and disorganized renal parenchyma. (D) Another patient with trisomy 18 and horseshoe kidney. The neonate had narrow hips that explain the fusion at the lower poles.

Figure 13.

VACTER association. (A) The trachea was open posteriorly to demonstrate a tracheo-esophageal fistula. (B) The photograph depicts esophageal atresia and tracheo-esophageal fistula. The probe was entered in the trachea and came out at the gastroesophageal junction. (C) Neonate with imperforate anus. (D) H&E-stained renal section with 10× lens, original magnification. There are several normal glomeruli at the upper part of the photograph, but they are intermixed with cystic tubules and in the lower half there are three cysts surrounded by concentric fibrosis.

Figure 14.

Bilateral renal agenesis (Potter sequence) (A) Newborn boy with characteristic Potter face with low-set, pliable ears, parrot-beaked nose, and receding chin. (B) Frontal view from the neonate’s face and upper body discloses fold under the eyes, low-set ears, flat nose, and broad hands. (C) Posterior view from organ block shows hypoplastic lungs and flat adrenal glands (arrows). Both kidneys were absent. (D) Dissected flat adrenal glands characteristic of renal agenesis.

Figure 15.

Caudal dysplasia syndrome (A) Open and eviscerated body of a fetus a 21 weeks. Black arrow points to absent sacrum. Both lower extremities are hypoplastic and contracted. (B) Horseshoe kidney from the same fetus.

Figure 16.

Sirenomelia (A) Lateral view of lower body. This fetus had absent external genitalia, imperforate anus with an anal tag, and a single lower extremity. (B) Lateral radiograph demonstrates a single femur and fibula. The foot was absent.

Figure 17.

Autosomal dominant polycystic kidneys and liver in an adult. (A) The kidneys were massively enlarged weighing 10 times the expected weight. The cut section reveals numerous round cysts in cortex and medulla. (B) The liver also contains multiple cysts involving almost the entire parenchyma. (C) Histologic section from the kidney (H&E stained) shows a few scattered glomeruli (arrows) and two large cysts at the bottom of the photomicrograph. One of the cysts is surrounded by chronic inflammation. Internal scale 1 mm. (D) This section depicts less glomeruli and more interstitial fibrosis. Internal scale 2 mm.

Figure 18.

Autosomal recessive polycystic kidneys. (A) The kidneys maintain the reniform shape, but are extremely enlarged. The cut section discloses numerous elongated and urine-filled cysts with radial orientation. (B) H&E-stained renal section with 2× lens, original magnification. There are preserved glomeruli, but the tubules are oriented with the longer axis perpendicular to the capsule. (C) The hepatic photomicrograph exhibits congenital hepatic fibrosis with numerous bile ducts with an open lumen in the portal plate (4× lens, original magnification). (D) Trichrome stained section (10× lens) stains the portal plate in blue and bile duct epithelium in red. Surrounding hepatocytes at the upper right and lower left are normal.