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KEY POINTS
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Key Points

  • Condition presents only rarely antenatally.

  • Incidence of pyloric atresia is 1 in 1 million livebirths. Hypertrophic pyloric stenosis occurs in 1.5–4 per 1000 livebirths.

  • Usually associated with polyhydramnios and a “single bubble.”

  • Differential diagnosis of a dilated fetal stomach includes duodenal atresia or stenosis, malrotation with midgut volvulus, duodenal duplication, and antral duplication.

  • Pyloric atresia can be associated with epidermolysis bullosa, a serious and often fatal skin condition that has autosomal recessive inheritance.

  • Delivery should occur in a tertiary center with pediatric surgical, dermatologic, and genetic expertise present.

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CONDITION
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Gastric outlet obstruction due to atresia or membranous antral web is rare, constituting one of the most unusual causes of gastrointestinal obstruction. On the other hand, gastric outlet obstruction due to hypertrophic pyloric stenosis is among the most common causes of gastrointestinal obstruction in the neonate. This condition only rarely presents antenatally (Zimmerman, 1978; Nebekura et al., 1983; Mitchell and Risch, 1993).

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A classification system for pyloric stenosis has been proposed: type A, a pyloric membrane or web; type B, the pyloric channel is a solid cord; type C, there is a gap between the stomach and the duodenum. Prenatal diagnosis should preempt consideration of other intestinal atresias (Usta, 2000; Ilce et al., 2003).

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INCIDENCE
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The incidence of pyloric atresia has been reported at 1 in 1 million livebirths, representing less than 1% of all gastrointestinal atresias (Geber and Aberdeen, 1965; Thompson et al., 1968). Hypertrophic pyloric stenosis occurs in 1.5 in 1000 to 4 in 1000 livebirths among whites, but it is less prevalent in blacks and Asians (Mitchell and Risch, 1993; Grant and McAleer, 1996). The incidence of prenatally diagnosed cases of these conditions is unknown.

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SONOGRAPHIC FINDINGS
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Prenatal diagnosis of pyloric atresia is associated with polyhydramniosin 61% of reported cases (Colin, 1989). The prenatal sonographic image usually shows polyhydramnios and associated gastric distention (Figure 71-1). If the fetus has recently vomited or if the obstruction is incomplete, the stomach may appear normal in size and polyhydramnios may be absent (Rizzo et al., 1995). This is especially true early in gestation, as polyhydramnios tends to develop during the third trimester. Sonographically, pyloric atresia and stenosis are associated with a “single bubble” as opposed to the “double bubble” observed in duodenal atresia. This appearance is due to either high-grade stenosis or complete atresia of the gastric outlet, resulting in marked dilation of the stomach. However, one should be cautious in the fetus with a “double bubble” sign, as this can be seen due to massive gastric distention and folding of the stomach on itself. The ultrasound beam can pass through the dilated fundus and then through the antrum, giving the impression of a double bubble. The ...

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