**2.3. Diagnosis**

Nowadays, the fetal bladder and kidneys may be visualized starting with 11 weeks (by transvaginal echography) or 12 weeks (by means of transabdominal echography). The fetal bladder and kidneys are located near the spine, having an elliptical shape [1, 2].

In the first trimester of pregnancy, the kidneys appear as an ovoid structure located on both sides of the spine (**Figure 1**) [1–4].

**d.** *Supernumerary kidney* is the rarest anomaly and consists of a third kidney with excretory cavities and its own vascularity, completely separated from the other kidney [1–8].

**a.** *Renal hypoplasia*. There are small congenital kidneys, located next to the median line and

**b.** *Kidney fusion*. There are bilateral symmetrical or asymmetrical mergers or unilateral

**c.** *The kidney in the horseshoe*. In 90% of the cases, kidneys join at the lower pole through a

**e.** *Unilateral asymmetric fusions*. There is a single kidney mass with a crossed ectopic kidney,

**a.** *Ectopic kidney*. A birth defect given by an abnormal (unilateral or bilateral) kidney position. The ectopic kidney is more often located on the left side. There are several ectopic kidney types: the caudal (lumbar, iliac, sacral) kidney, the cranial kidney and the crossed kidney.

**b.** *Renal dystopia*. Initially, in embryonic life, the hill and pelvis are located in the anterior part, and then they undergo a rotation around the longitudinal axis, until they reach the

These are large and hyperechogenic kidneys, including renal ciliopathies. These conditions may be divided into autosomal dominant diseases and autosomal recessive disorders, including the polycystic kidney disease, renal dysplasia, glomerulocystic kidney disease (trisomy 13 and trisomy 18, Beemer syndrome), multicystic dysplastic kidneys (MCDK), medullary cystic dysplasia (Meckel-Gruber and Beckwith-Wiedemann syndromes, as well as congenital

Nowadays, the fetal bladder and kidneys may be visualized starting with 11 weeks (by transvaginal echography) or 12 weeks (by means of transabdominal echography). The fetal blad-

der and kidneys are located near the spine, having an elliptical shape [1, 2].

**b.** *Kidney hyperplasia*. There is a large kidney, after ruling out any other cause [5–7].

**d.** *Bilateral asymmetric mergers*. One of the kidneys is smaller than the other.

known as 'the sigmoid kidney', usually located in the pelvis [7–10].

**II.** Renal size abnormalities

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**III.** Kidney's shape abnormalities

parenchymal or fibrous bridge.

**VI.** Renal position abnormalities

median side [1–4, 7].

infections) [10–13].

**2.3. Diagnosis**

**V.** Multicystic renal dysplasia

asymmetry.

excretory cavities. The renal function is normal or low.

**a.** *Lobular kidney*. There is a persistence of fetal lobulation.

Renal urine production begins during week 9 of embryonic life, making it possible to visualize the bladder, as a fluid collection in the fetal pelvis. The bladder appears spherical and transonic and is located between the iliac bone centers of ossification, in the lower pelvis. It can be visualized starting with the ninth week of pregnancy, and the umbilical arteries can be visualized laterally next to the bladder. Beyond the first trimester, the bladder will fill and empty in an intermittent manner, every 25–30 minutes, due to the influence of hormonal factors on the bladder (**Figure 2**) [2, 3].

Normal ureters cannot be visualized by means of echography. The ratio of renal circumference to abdominal circumference is 0.27–0.30 and remains constant during pregnancy [8].

Evaluation of the urinary tract also requires the evaluation of the amniotic fluid volume. After the 14th week of intrauterine life, the amniotic fluid comes mainly from the production of fetal urine and only one-third of its quantity comes from the pulmonary fluid [2, 5].

For a correct diagnosis, the clinician has to perform a complete examination in all of the three planes, the coronal, the sagittal and the longitudinal plane, using 2D grayscale and color Doppler. The examination should be complete. Sometimes, the ultrasound examination has to be completed by another screening method. Due to the association between renal malformations and other congenital defects or chromosomal anomalies, performing an invasive diagnosis method may be required [14].

The renal pelvic dilatation (RPD) is the most common of the abnormalities that can be detected during antenatal ultrasonography and is probably the most frequent sign of a reno-urinary

**Figure 1.** Fetal kidneys in the first trimester of pregnancy.

urinary malformations encountered in children are vesicoureteral reflux (VUR), obstructive

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Fetal hydronephrosis may result in a number of conditions, like pelvic or vesicoureteral junction obstruction, posterior urethral valves, vesicoureteral reflux, pelvic-ureteric junction obstruction and other rare congenital anomalies [12, 13]. A clear definition of hydronephrosis would be that it is a dilatation of the calyces and the renal pelvis of over 10 mm or more than 50% of the anteroposterior diameter of the kidney. This dilatation of the urinary system may occur at the upper urethral segment, ureters, bladder or kidney pelvis. Pyelectasis is the dila-

By some authors, the clinician can diagnose hydronephrosis if the renal pelvic AP diameter is increased over 4 mm in the second trimester and 7 mm in the third trimester [3, 11, 15] (**Figure 4**). A renal pelvic AP diameter > 15 mm is strongly associated with a pathology of the urinary tract that requires treatment after birth. However, in the majority of cases, the renal pelvis is mildly or

There is no clear consensus on the follow-up and management of mild or moderate hydronephrosis observed on antenatal ultrasound, although it is generally accepted that a postnatal assessment should be performed if the AP diameter of the renal pelvis exceeds 10 mm at any

megaureter, posterior urethral valve and megacystis [11].

tation of the renal pelvis only (**Figure 3**) [6, 15].

moderately dilated, and no cause is identified [16].

**Figure 3.** Second trimester: different aspects in hydronephrosis cases.

point in gestation [17].

**Figure 2.** The bladder in the first trimester of pregnancy.

anomaly. The diagnosis of the RPD is based on an increased anteroposterior diameter of the renal pelvis in the transverse plane, and the value allows classification: severe, moderate or mild RPD. Normal values of anteroposterior diameter of the kidney pelvis are up to 4 mm at week 16 of pregnancy, less than 7 mm at 28 weeks of pregnancy and less than 10 mm postnatal [15].

In many cases a transient dilatation occurs. This situation is caused by narrowing or natural folds of the urinary tract that may occur during the early stages of development. Transient dilatation is usually less than 6 mm in the second trimester and less than 8 mm in the third trimester. It usually resolves spontaneously or disappear postnatally [16].


#### **2.4. Uropathies**

Uropathies are the most common reno-urinary abnormalities diagnosed during the prenatal period and may be caused by obstructive or nonobstructive factors [10–13]. The most common urinary malformations encountered in children are vesicoureteral reflux (VUR), obstructive megaureter, posterior urethral valve and megacystis [11].

Fetal hydronephrosis may result in a number of conditions, like pelvic or vesicoureteral junction obstruction, posterior urethral valves, vesicoureteral reflux, pelvic-ureteric junction obstruction and other rare congenital anomalies [12, 13]. A clear definition of hydronephrosis would be that it is a dilatation of the calyces and the renal pelvis of over 10 mm or more than 50% of the anteroposterior diameter of the kidney. This dilatation of the urinary system may occur at the upper urethral segment, ureters, bladder or kidney pelvis. Pyelectasis is the dilatation of the renal pelvis only (**Figure 3**) [6, 15].

By some authors, the clinician can diagnose hydronephrosis if the renal pelvic AP diameter is increased over 4 mm in the second trimester and 7 mm in the third trimester [3, 11, 15] (**Figure 4**). A renal pelvic AP diameter > 15 mm is strongly associated with a pathology of the urinary tract that requires treatment after birth. However, in the majority of cases, the renal pelvis is mildly or moderately dilated, and no cause is identified [16].

There is no clear consensus on the follow-up and management of mild or moderate hydronephrosis observed on antenatal ultrasound, although it is generally accepted that a postnatal assessment should be performed if the AP diameter of the renal pelvis exceeds 10 mm at any point in gestation [17].

**Figure 3.** Second trimester: different aspects in hydronephrosis cases.

anomaly. The diagnosis of the RPD is based on an increased anteroposterior diameter of the renal pelvis in the transverse plane, and the value allows classification: severe, moderate or mild RPD. Normal values of anteroposterior diameter of the kidney pelvis are up to 4 mm at week 16 of pregnancy, less than 7 mm at 28 weeks of pregnancy and less than 10 mm postnatal [15]. In many cases a transient dilatation occurs. This situation is caused by narrowing or natural folds of the urinary tract that may occur during the early stages of development. Transient dilatation is usually less than 6 mm in the second trimester and less than 8 mm in the third

• Many authors concluded that for an accurate diagnosis, the assessment of the renal and urinary function may be performed by ultrasound [5, 6]. The following statements gained

• The absence of the bladder filling may indicate renal agenesis and bilateral ureteral obstruction.

• The ureteral dilatation may be caused by a lower obstruction of the inferior urinary tract. • The echogenicity of renal parenchyma cannot be considered for the renal function assessment.

Uropathies are the most common reno-urinary abnormalities diagnosed during the prenatal period and may be caused by obstructive or nonobstructive factors [10–13]. The most common

• The increasing rebound pressure in the renal artery may cause renal function [5–12].

trimester. It usually resolves spontaneously or disappear postnatally [16].

**Figure 2.** The bladder in the first trimester of pregnancy.

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• The amount of amniotic fluid is an indirect indicator of the kidney function. • The bladder filling indicates the normal functioning of at least one kidney.

• The bladder distension may hide a urethral reflux problem.

acceptance:

**2.4. Uropathies**

**Figure 4.** Hydronephrosis in the third trimester of pregnancy.

Many studies show that a right or left prenatal AP renal pelvic diameter > 4 mm is associated with a higher risk of postnatal hydronephrosis compared with a right and left prenatal AP renal pelvic diameter ≤ 4 mm [15, 16]. Male neonates have a higher risk of postnatal hydronephrosis than females. These results can assist in establishing the appropriate follow-up method and evaluation of fetuses with renal pelvic dilatation [18, 19].

**b.** The ureteropelvic junction obstruction

the double renal artery.

**c.** Obstruction of the ureterobladder junction

Obstruction of the ureterobladder junction (obstructive megaureter) or obstruction on pyeloureteral junction is one of the most common causes of hydronephrosis found in children, its incidence being 1 case in 1000–2000 newborns. In this situation, hydronephrosis may be caused by an abnormal shape of the ureteral junction—the existence of the ureteral valves and the mucosal fold at this level. Like many other abnormalities, this pathology occurs much more frequently in males, usually unilaterally and especially on the left side [10, 14]. The ultrasound diagnosis is based on the observation of the increase of the anteroposterior diameter of the kidney, a degree of kidney pyelectasis. If the obstruction is unilateral and the filling of the bladder is normal, the normal amount of amniotic fluid will be preserved.

**Figure 5.** Coronal section and high-definition power color Doppler, in a supernumerary kidney cases. Visualization of

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In most cases this condition does not produce symptoms after birth; in 10–15% of the cases, it regresses spontaneously, but sometimes repeated evaluation is needed [1–8].

This condition is the cause of approximately 5–10% of all cases of dilatation of the urinary tract. Ultrasound diagnosis is based on dilated urethra, with renal pelvis dilatation and normal bladder image. The cause of the disease is the dysfunction of the lower ureter, the outcome is favorable and the pathologic aspects disappear postnatally in many cases [16] (**Figure 6**).

The normal ureter size in children is up to 5 mm. Normal ureter cannot be detected during prenatal ultrasound examination. It can only be detected if it is dilated to a size greater than 7 mm and is observed like a translucent structure. The dilated ureter should be differentiated from full intestinal loops. Pathological dilatation of the ureter is more common

When the damage is bilateral, the oligoamnios/oligohydramnios may appear.

in male patients, usually appearing to be unilateral (**Figure 7**) [15–17].
