| Discussion: |
The two most common forms of distal ileal obstruction are ileal atresia and meconium ileus. An intrauterine ischaemic insult to the developing intestine results in atresia or, more rarely, stenosis. It can affect any portion of the jejunum or ileum. The varieties include atresia with the two blind ends lying in apposition or separated by a fibrous band, and atresia with a gap between the ends often associated with a mesenteric defect. A rare variety is one in which the intestine spirals around the mesenteric artery with the mesentery running in a spiral from the central vessel to the intestine and is known as an "apple peel" deformity. This type has a familial incidence. The others are isolated. Intrauterine volvulus of part of the intestine may also cause atresia. Atresias may be multiple within the small bowel. The clinical presentation is with bilious vomiting, the age of onset being determined by the level of the atretic segment, the higher the lesion the earlier the onset of symptoms but most infants present within the first 24 hours post delivery. Abdominal distension is also present in children with low atretic lesions.
The radiological appearance is that of distended loops of bowel with fluid levels, the number of loops being determined by the level of the atresia. The higher the most proximal atretic lesion the fewer the number of distended loops. Intrauterine perforation of the bowel with extrusion of meconium into the peritoneal cavity is reflected on the radiographs by the finding of calcified meconium within the peritoneal cavity. In ileal atresia the diagnosis may be delayed as the infant can pass meconium which is present in the bowel distal to the atretic segment, thus causing the illusion of the bowel continuity being intact. In ileal atresia the loop of bowel proximal to the atresia may become disproportionately distended to the rest of the loops of bowel and be filled with meconium mixed with fluid to give a bubbly appearance which can be confused with the appearance of meconium ileus seen in cystic fibrosis infants. In the high intestinal atresias, contrast studies are not indicated. In the lower lesions water soluble enemas are indicated to determine the cause of the abdominal distension. In ileal atresia a microcolon is demonstrated, the contrast outlining the whole colon and appendix and sometimes a portion of collapsed ileum. Unlike infants with Hirschsprung's disease the rectum is distensible.