**2. Congenital anomalies overview**

Congenital anomalies of the abdominal contents involve organs of the gastrointestinal tract, kidneys and urinary tract, suprarenal glands, and genital organs (mainly the ovaries).

Anomalies in the fetal abdomen are diagnosed either by the lack of visualization of normal structures or evidence of abnormal images during the anomalies screening ultrasound examination. Therefore, obtaining and documenting standard normal images of the abdomen is of crucial importance.

This chapter is structured in 4 subsections:


#### **2.1. Normal ultrasound images of the abdomen**

At the midtrimester routine ultrasound scan, there are a couple of images that must be obtained according to ISUOG guidelines [1], images that can rule out most of the abdominal pathological conditions.

after 16 weeks of gestation. Nomograms of stomach size have been imagined at different gestational age [2]. Hyperechoic mass of uncertain origin may be seen inside the stomach and may disappear at the following examinations without pathological significance [3]. • fetal liver is an hypoechogenic structure that occupies the section on the right of the stomach. • gall bladder is an ovoid, hypoechoic structure on the right and under the intrahepatic part

**Figure 2.** Sagittal section of the fetal abdomen—the continuity of the anterior abdominal wall is obvious (pa), the cord

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• the umbilical vein has a caudal trajectory, penetrates the liver and connects with the left portal vein. Actually, the umbilical vein is the left portal vein, because the right portal vein regresses

The sagittal section at the abdominal level is essential for assessing the integrity of the anterior abdominal wall, because the insertion of the umbilical cord and the wall above and below the insertion can be visualized. Differentiating between the internal structures of the abdomen can be difficult, because the liver and intestinal loops have similar echogenicity. Between 8 and 10 weeks of gestation, the physiological gut herniation can be visualized by ultrasound, as a hyperechoic mass at the base of the umbilical cord. Reintegration occurs between 10 and

At a lower transverse section of the abdomen, the kidneys, small bowel, and colon can be seen

• the kidneys are located on both sides of the spine; their adult similar shape can be recognized from 12 weeks but the medular/cortical differentiation is obvious starting from 15 weeks of gestation. The fluid filled structure of the calyces is a useful landmark to identify the kidneys. Corticomedullary differentiation (CMD) is determined according to echogenicity of the cortex and the medulla, considering that during the prenatal period, the

• the anterior abdominal—skin, subcutaneous cellular tissue, and muscles.

insertion (co), stomach (s), urinary bladder (vu), diaphragm (d), and bowel (i).

12 weeks and it is complete at approximately 11 weeks and 5 days.

of the umbilical vein.

at 6–7 weeks.

as the following:

First step of the examination should be visceral situs assessment, by demonstrating the position of the stomach, liver veins, abdominal aorta, and superior cava vein as seen in **Figures 1** and **2**.

The abdominal transverse section at the umbilical vein–portal sinus is the level for abdominal circumference measurement and a standard image to identify some important structures:

• fetal stomach-an anechoic structure of bean-like form. It can be seen from 9 weeks, but at 14 weeks, the different parts of the stomach can be seen and gastric peristalsis can be detected

**Figure 1.** Transverse section of the fetal abdomen—the structures that can be seen are: stomach (s), umbilical vein (uv), liver (l), and suprarenal gland (sr).

**2. Congenital anomalies overview**

248 Congenital Anomalies - From the Embryo to the Neonate

This chapter is structured in 4 subsections:

2.2. Anomalies consisting of absent structures.

**2.1. Normal ultrasound images of the abdomen**

2.1. Normal aspect of the fetal abdomen.

2.4. Abdominal wall anomalies.

liver (l), and suprarenal gland (sr).

crucial importance.

cal conditions.

Congenital anomalies of the abdominal contents involve organs of the gastrointestinal tract,

Anomalies in the fetal abdomen are diagnosed either by the lack of visualization of normal structures or evidence of abnormal images during the anomalies screening ultrasound examination. Therefore, obtaining and documenting standard normal images of the abdomen is of

At the midtrimester routine ultrasound scan, there are a couple of images that must be obtained according to ISUOG guidelines [1], images that can rule out most of the abdominal pathologi-

First step of the examination should be visceral situs assessment, by demonstrating the position of the stomach, liver veins, abdominal aorta, and superior cava vein as seen in **Figures 1** and **2**. The abdominal transverse section at the umbilical vein–portal sinus is the level for abdominal circumference measurement and a standard image to identify some important structures:

• fetal stomach-an anechoic structure of bean-like form. It can be seen from 9 weeks, but at 14 weeks, the different parts of the stomach can be seen and gastric peristalsis can be detected

**Figure 1.** Transverse section of the fetal abdomen—the structures that can be seen are: stomach (s), umbilical vein (uv),

kidneys and urinary tract, suprarenal glands, and genital organs (mainly the ovaries).

2.3. Abnormal structures present in the abdomen: cystic or echoic masses.

**Figure 2.** Sagittal section of the fetal abdomen—the continuity of the anterior abdominal wall is obvious (pa), the cord insertion (co), stomach (s), urinary bladder (vu), diaphragm (d), and bowel (i).

after 16 weeks of gestation. Nomograms of stomach size have been imagined at different gestational age [2]. Hyperechoic mass of uncertain origin may be seen inside the stomach and may disappear at the following examinations without pathological significance [3].


The sagittal section at the abdominal level is essential for assessing the integrity of the anterior abdominal wall, because the insertion of the umbilical cord and the wall above and below the insertion can be visualized. Differentiating between the internal structures of the abdomen can be difficult, because the liver and intestinal loops have similar echogenicity. Between 8 and 10 weeks of gestation, the physiological gut herniation can be visualized by ultrasound, as a hyperechoic mass at the base of the umbilical cord. Reintegration occurs between 10 and 12 weeks and it is complete at approximately 11 weeks and 5 days.

At a lower transverse section of the abdomen, the kidneys, small bowel, and colon can be seen as the following:

• the kidneys are located on both sides of the spine; their adult similar shape can be recognized from 12 weeks but the medular/cortical differentiation is obvious starting from 15 weeks of gestation. The fluid filled structure of the calyces is a useful landmark to identify the kidneys. Corticomedullary differentiation (CMD) is determined according to echogenicity of the cortex and the medulla, considering that during the prenatal period, the normal renal cortex is as echogenic as the liver or spleen and that the normal renal medulla is relatively hypoechogenic, which leads to a well-defined CMD [4].

*2.2.1. Esophageal atresia*

• type A: without fistula • type B: proximal fistula

• type C: distal fistula (88% of cases)

• type D: double fistula, proximal, and distal

• type E: existing fistula without concomitant atresia

anomalies, radial aplasia, and single umbilical artery [9].

of cases to the tracheoesophageal fistulae association.

and 44% of the cases cannot be diagnosed.

ach, the most frequent are:

diagnosed during the prenatal period [7].

There are five types of esophageal atresia, but the most common one after de Jong is the type with esophageal stump and trachea-esophageal connection below the interruption. In such cases, it is important to look after other indirect signs, like polyhydramnios and small for gestational age. Many of the anomalies are nonisolated [7]. Still, 44% of the anomalies are not

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Esophageal atresia is a condition defined by the lack of continuity between the proximal and the distal esophagus. The missing portion is the middle one and the main cause is poor blood flow. The anomaly appears during the 8th week of pregnancy when the primitive intestine fails to divide forming the trachea anteriorly and esophagus posteriorly. According to de Jong, in 90% of cases, esotracheal fistulae are associated. There are five types of esophageal atresia considering the anatomical location of the defect and the existence of the tracheoesophageal fistula [7]:

The incidence of this anomaly is 1:3500 live born and usually is nonisolated, being associated with CNS anomalies, VACTERL association, T21, T18, diaphragmatic hernia, and abdominal wall anomalies. [7]. Twenty percent of cases of the associations are with chromosomal anomalies (trisomy 13, 18, 21) [8] and cardiac defects may be present in 50% of cases. VACTERL syndrome is comprised of vertebral defects, ventricular septal defect, anal atresia, esotracheal fistula, renal

Ultrasound diagnosis of esophageal atresia can be missed in pregnancy according to Brandberg

The prenatal diagnosis of esophageal atresia is difficult due to the absence of specific signs. The rate of detection varies between 8 and 24% [10, 11], and the lack of detection is due in 85%

Prenatal esophageal atresia must be suspected if polyhydramnios is present after the 25th week of gestation and if the gastric pouch is absent. Sometimes, gastric secretions are sufficient to distend the gastric pouch, and make the diagnosis more difficult; if an esotracheal fistula is present, the gastric pouch may appear normal. Sometimes, the distal dilated portion of the esophagus may be observed as a hypoechoic area in the mediastinum, behind the heart (blind pouch aspect). Although the sign has a great diagnostic value, it is rarely present before 25 weeks of

The differential ultrasound diagnosis can be made with other conditions with absent stom-

gestation [8, 12, 13]. The detection rate is improved if an antenatal MRI is performed.


The echogenicity of the colon is established in comparison to other structures such as the liver or bladder:


Coronal or sagittal section of the fetal abdomen allows the visualization of the urinary bladder. It can be identified starting at 11–12 weeks of gestation as an anechoic mass with a thin wall, delineated by two umbilical arteries.

#### **2.2. Absence of normal abdominal structures**

The most common condition is the nonvisualization of the stomach, kidneys, or urinary bladder.

Nonvisualization of the gall bladder occurs in rare chromosomal diseases, mucoviscidosis, and in 20% of the fetuses with biliary atresia [6].

Absent stomach or small stomach can be associated with mechanical or functional absence of stomach filling:

