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Definitions
Atresia: derives from greek α-τρησιαwhich means absence of perforation. In a gastrointestinal atresia there is an interruption of the lumen continuity at some point of the gastrointestinal "tube", with eventual dilation of the proximal blind end. The most frequent gastrointestinal atresias are represented by esophageal, duodenal, and anal atresia.
Omphalocele and gastroschisis: they both derive from greek ομϕαλο-κηλη and γαστρο-σχισιç which respectively mean "protrusion (of an intra-abdominal structure) through the umbilical cord insertion" and "tear of the abdominal wall". In both cases it results in herniation of parts of the gastrointestinal structures through the fetal abdominal wall. In omphalocele the herniated structures are covered from the peritoneum and the umbilical cord's amnion. In gastroschisis, the herniated structures are in direct contact with the amniotic fluid.
Physiologic herniation of the bowel-normal process in which a loop of the midgut herniates into the proximal part of the umbilical cord (physiologic exomphalos) due to the relatively reduced intraabdominal space, usually from 7th to 11th week of gestation. At around 11 menstrual weeks the midgut has completely re-entered into the fetal abdomen.
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Most parts of the gastrointestinal tract (GIT) may appear as "silent" structures during a routine ultrasonographic examination, which becomes evident when an abnormality is present, such as increased echogenicity or dilation due to obstruction. Nevertheless, careful observation of the fetal gastrointestinal system will reveal its typical appearance on ultrasound and its main differential features compared to other systems: a relevant ultrasonographic variability, not only throughout the pregnancy, but even during the same examination. In fact, swallowing, stomach emptying, and intestinal peristalsis can considerably change the appearance of the GIT during a single examination.
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The detection of an intraabdominal abnormality can become particularly challenging due to a variety of systems/ organs that could be involved, including the GIT, genitourinary system, adrenal glands, spleen, liver, pancreas, and lungs. Many of these abnormalities do not give a direct ultrasonographic sign, but may be suspected on the observation of indirect abnormal findings. Topography of the observed abnormality, fetal sex, and gestational age are significantly useful to determine its possible origin.
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Another feature of the GIT pathologies rendering their antenatal diagnosis a difficult task is the frequent absence of any ultrasonographic evidence before the third trimester. Furthermore, some abnormalities may not give any ultrasonographic sign during the whole pregnancy, such as an esophageal atresia with tracheal fistula and an almost normally fluid-filled stomach.
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The outcome of a gastrointestinal anomaly depends, as for other systems, on the feasibility of the surgical correction, the extension of the damage, and the association with other structural or chromosomal abnormalities.
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A discussion of the spleen is included in this chapter. Although the spleen does not make up part of the gastrointestinal system, a specific chapter about spleen and the immune system is unnecessary from an ultrasonographic point of view.
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