and Marcelo Zugaib4
São Paulo University, Bauru, Brazil
Parisian University, Bauru, France
Member of International Fetal Medicine and Surgery Society, Bauru, Brazil
Obstetrics, University of São Paulo, Bauru, Brazil
Malformations of the kidneys and urinary tract constitute the second most commonly diagnosed group of diseases in the prenatal period, with an incidence of 0.3–0.5%. Most cases of fetal urinary tract malformation are diagnosed during routine examination. However, the most important indication for researching urinary tract malformations is the finding of decreasing amniotic fluid or the observation of a small uterus for gestational age.
A proper evaluation of the urinary tract should include at least one cross-section of the fetal abdomen at the level immediately above the renal hilum, a longitudinal section paramedian through each kidney’s store, visualization of the fetal bladder, and evaluation of the amount of amniotic fluid.
In the cross-section the kidney’s stores should be identified at each side of the column. It is in this section that the anteroposterior diameter of the renal pelvis is measured, and in which the renal pelvis can be measured when it is visible. The standardization of this measurement is important, because it enables us to monitor the case followed, and it is the universal section proposed for the diagnosis of hydronephrosis.
As previously described, the renal pelvis varies according to gestational age, and to accompany its growth, there are appropriate tables. In practical terms, we consider a renal pelvis to be increased when it is above 5 mm at 24 weeks or above 10 mm at 32 weeks. It should be noted if the dilatation affects merely the renal pelvis, which is known as pyelectasis, or if there is involvement (swelling) of the renal calyces, which is called ureteropelvic dilation, and represents a more advanced stage of expansion.
In a longitudinal section, the lateromedial and longitudinal renal measurements can be obtained. By performing this last measurement, care should be taken not to include the adrenal gland, which appears as a slightly hypoechoic structure with the upper pole of the kidney. It is in this section that the measurement of renal thickness is obtained.
The calyx pyramidal system can be observed and the renal parenchyma may also be evaluated, usually on an enlarged image. The normal parenchyma has a slightly higher echogenicity in the cortex compared with marrow, called cortical differentiation, which is lost in cases of renal dysplasia, in which the parenchyma may appear globally hyperechogenic and often presents cortical cysts indicating terminal functional impairment.
The ureters are usually not displayed on the ultrasound because of its virtual light, not filled with liquid, but when they are dilated, they may be identified as cystic structures, usually in the form of “stacked coins” extending from the renal pelvis to the fetal bladder.
The fetal bladder can usually be identified in the fetal pelvis along the iliac bones. The filling and emptying of the normal fetal bladder is an easily demonstrable phenomenon in ultrasound. When the bladder becomes dilated (megacystis), it can occupy the whole fetal abdomen.
The sensitivity of ultrasound for detecting these abnormalities, especially the obstructive ones, increases with gestational age, reaching 80% at 28 weeks’ gestation. Although detection of such abnormalities during the prenatal period is frequent, often an accurate diagnosis of the lesion, in addition to its prognostic value, is difficult to assess.
The evaluation of the amount of amniotic fluid is critical in the evaluation of urinary tract malformations. Bilateral or infravesical urinary tract abnormalities can lead to a lack of production or of the disposal of urine into the amniotic fluid, causing it to diminish markedly.
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10.1 Urinary Tract Malformations
Malformations of the urinary tract can be divided regarding ultrasound aspects into: urinary tract dilatation; anomalies of numbers; anomalies of merger position; cystic abnormalities, etc.
Cross section of the fetal abdomen showing normal appearance of the kidney (small white arrows) showing normal left kidney (RE) and right kidney (RD). E = fetal stomach; RINS NORMAIS = normal kidneys
Cross section of the fetal abdomen showing normal appearance of the kidney (arrows) anterolaterally the spine (c) observing the parenchyma with normal cortico differentiation and renal pelvis (VB = gallbladder)
Longitudinal section laterally deviated to the left to show normal aspect of left kidney (RIM ESQ, arrows) and its position related to fetal column (C)
Longitudinal section at the level of the renal hilum, where the aorta and the adrenal gland (sr) (slightly hypoechoic) are clearly observed supero-lateral to the kidney (arrow). A = aorta
Longitudinal section laterally deviated to the left where circular anechogenic images are seen inside kidney parenchyma (M) representing medular lay of the kidney and Malpighi pyramides surrounding renal pelvis (P)
Kidney longitudinal section in which the cortex (c) and spinal cord (m, arrow) can be clearly differentiated
Cross section of the fetal pelvis evidencing the fetal bladder (arrow) normal appearance. The fetal bladder is seen between iliac bones (I). F = femoral bones
Cross-section of the fetal pelvis demonstrating the normal appearance of the fetal bladder (b), with the bifurcation of the two arteries (arrows)
Cross-section of the fetal abdomen at the level of the adrenal (arrows). Note their relationship with the spine (c). The presence of the stomach (e) at the same cutting level, shows that the cut of the adrenals is higher than that of the kidneys
Cross-section of the fetal abdomen showing empty kidney stores in a case of bilateral renal agenesis (Cliché given by M. C. Aubry) (black and white arrows)
Cross-section of the fetal abdomen showing an empty left renal store (LOJA RENAL ESQ VAZIA) and right normal aspect of the kidney, in a case of left renal agenesis. rd = right kidney (arrows), c = column
Left: coronal section of kidney stores showing the right kidney (rd) of normal appearance (arrows). Right: empty left kidney store
Cross section of the fetal abdomen at the level of renal lodges in a case of fetal bilateral renal agenesis. Notice that there is no amniotica fluid. PLA = placenta and AB = fetal abdomen
Bilateral renal agenesis, now in a longitudinal section using a color Doppler window showing the descending aorta with no renal artery going out from it (arrows)
Longitudinal section showing the left kidney store (arrows) with slight dilation of the pelvis (w) and duplicate right kidney. Note the presence of two right pelvises (p)
Longitudinal section of the fetal abdomen showing duplicate left kidney, with a large cyst in the upper pole. ur = ureter
Longitudinal cut of fetal pelvis showing a full fetal bladder with ureterocele aspect inside it (arrow).
Left: coronal section of a duplicate left fetal kidney. Right: cross-section of the fetal bladder with ureterocele. c = upper pole cyst, b = bladder, u = ureterocele (arrow)
Appearance of a longitudinal section of a duplicate fetal kidney noting the presence of two pelvises (P). This finding leads us to look for a bladder ureterocele coming from the upper pole
Cross-section of the fetal abdomen showing a horseshoe kidney (arrows) around the aorta (AO). col = column, f = anterior surface of the fetal abdomen
Cross-section fetal abdominal horseshoe kidney case (arrows). Note that to set up the previous horseshoe kidney, the transducer flow direction should be skewed (= oblique section of the aorta)
longitudinal to the left view showing an ectopic left kidney (arrow) near the hipbone (to the right of the arrow) and too close to fetal bladder.
Same case of Fig. 10.22 now in a coronal oblique view confirming ectopic left kidney (arrows, RIM ESQ ECTOPICO). Notice fetal right kidney (arrow, RIM D) a little bit up close to the aorta (AO). IL = hipbone
Cross section of the fetal pelvis noting the presence of pelvic kidney (arrow). Note the renal pelvis (P) at the hipbone level (I) (c = column)
Cross-section of dysplastic kidney (RD) in the case of Meckel–Gruber syndrome characterized by encephalocele, polydactyly, and renal dysplasia. Note increased volume and renal cortico-medullary absence of differentiation
Cross-section of the fetal abdomen (right) showing the kidneys (Rc and Rd) with a dysplastic aspect (col = column) in the same case of Meckel–Gruber syndrome as in Fig. 10.25, where an occipital encephalocele (e) is visualized on the left
Cross section of the fetal abdomen showing big hyperechogenic fetal kidneys (RD and RE) with a dysplastic aspect (hyperechoic parenchyma and without corticomedullar differential) but renal pelvis are still identifiable corresponding a Infantile polycystic kidney disease (recessive autosomal disease so consanguinity is often present or a previous case is reported. Differential diagnosis should be made with Meckel Gruber Syndrome.
Left: dysplastic kidney (arrows) with parenchymal echogenicity and loss of cortical differentiation (arrows). Right: cross-section showing echogenic enlarged kidneys without cortico-medullary differential diagnosis
Cross-section of the fetal abdomen showing hyperechoic kidneys (R), dysplastic, with the presence of ascites (arrows) and low amount of fluid (LA)
Section of the fetal abdomen showing the presence of increased kidney volume and lack of cortico-medullary differentiation and the presence of microcysts of the polycystic kidney infantile form (arrows)
Longitudinal section (right) and cross-section (the left) of the same case as in Fig. 10.30, where the hyperechogenic aspect of bilateral renal parenchyma (arrows) can best be seen
Cross-section of the fetal abdomen evidencing kidneys with bilateral multicystic (C) dysplasia (right = right kidney, left = left kidney; r = spine, c = large not communicating cysts which are typical of this pathology)
Cross-section of the fetal abdomen evidencing kidneys with bilateral multicystic dysplasia (right on the figure = right kidney, left on the figure = left kidney). Notice that there is no amniotic fluid as this pathology starts in a pre metanephrons time in embryologic sequence, so no functional renal parenchyma is observed
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