Small Intestine: Anatomy and Structural Anomalies

This chapter presents a brief synopsis of the major events in midgut morphogenesis as a basis for understanding the congenital anomalies of the small intestine. The small intestine is composed of four concentric layers: the serosa, muscularis propria, submucosa, and mucosa. Duplications of the gastrointestinal tract are rare, congenital cystic anomalies attached to the intestinal mesenteric border. They are usually lined by gut mucosa but, like Meckel diverticula, they may contain heterotopic gastric mucosa or less commonly pancreatic, squamous, thyroid, or bronchial epithelium as well as lymphoid aggregates. Although gastroschisis and omphalocele both result from abdominal wall defects, these rare disorders are distinct entities. Intestinal intussusception is one of the most common causes of small bowel obstruction in children younger than 2 years of age but it is an unusual cause of bowel obstruction in adults.