lumen may occur anywhere along the intestine. As already described, duodenum is the commonest site affected by these anomalies. However, stenosis and atresias also occur in jejunum and ileum, or even in the colon. The most frequent type of atresia is called diaphragmatic atresia. In this anomaly the mucosa and submucosa form a trans-verse diaphragm, which obstructs the gut lumen. In other types of atresia, a segment of intestine may be represented by a fibrous cord or may be completely absent. As already discussed, stenosis and atresias are supposed to result form an inadequate re-canalization of the gut lumen during the 7th and 8th weeks of development. The recent evidence indicates that most of
the jejunal and ileal atresias result from fetal vascular accidents which result in partial or complete occlusion of blood supply to a segment of the developing gut. The vascular accidents may be caused by a variety of factors including volvulus, gastroschisis, omphalocele, etc. The affected part of the gut undergoes necrosis, resulting in stenosis or atresia.