Duodenal atresia is the congenital absence or complete closure of a portion of the lumen of the duodenum. It causes increased levels of amniotic fluid during pregnancy (polyhydramnios) and intestinal obstruction in newborn babies. Sometimes there is still a passage to distal, mostly when there is a duodenal web.
Intestinal atresia is a malformation where there is a narrowing or absence of a portion of the intestine. This defect can either occur in the small or large intestine. The different types of intestinal atresia are named after their location: jejunal-, ileal- and colon atresia. The most common cause of non-duodenal intestinal atresia is a vascular accident in utero that leads to decreased intestinal perfusion and ischemia of the respective bowel segment. This leads to narrowing, or in the most severe cases, complete obliteration of the intestinal lumen. In the case that the superior mesenteric artery, or another major intestinal artery, is occluded, large segments of bowel can be entirely underdeveloped. Classically, the affected area of bowel assumes a spiral configuration and is described to have an "apple peel" like appearance; this is accompanied by lack of a dorsal mesentery. Ileal atresia can also result as a complication of meconium ileus.