Small Intestine: Imaging Approach and Differential Diagnosis

Embryology and Congenital Malformations

The small intestine and the right side of the colon constitute the embryologic midgut, which herniates into the umbilical cord during the process of marked elongation in fetal development. Following a 270° counterclockwise rotation, the midgut returns to the peritoneal cavity. Errors during this complex series of events are common, resulting in varying degrees of malrotation ± volvulus. This may result in bowel obstruction and ischemia and may present in infancy or be delayed into adult life.

In the fetus, the omphalomesenteric or vitelline duct connects the distal small bowel (SB) with the yolk sac. By birth, the vitelline duct has usually atrophied and disappeared; failure of involution results in a Meckel diverticulum , a blind outpouching from the distal ileum.