The small bowel is a tortuous tubular organ, 600–800 cm in length. Anatomically, it lies between the pylorus and ileocecal valve. It comprises three segments: the duodenum, jejunum, and ileum. The duodenum is the most proximal and shortest segment of the small bowel, with a mean length of 25 cm. It is shaped like a C‐loop. This is the only segment located in the retroperitoneal space and is therefore relatively fixed. It includes the duodenal bulb, and the second, third and fourth portions, and it extends up to the ligament of Treitz. The ampulla of Vater lies in the second portion of the duodenum. The remainder of the small bowel is suspended in the peritoneal cavity by a broad‐based mesentery, and is freely mobile. The proximal 40% of this portion is the jejunum and the remaining distal 60% is the ileum. The luminal surface of the small bowel has numerous folds called the plicae circulares. The plicae are most prominent in the proximal small bowel, and decrease in number distally. The length and mobility of the small bowel have posed challenges to its evaluation in the past.

The introduction of capsule endoscopy and deep enteroscopy has led to a significant improvement in endoscopic evaluation and management of small bowel disorders, including obscure gastrointestinal bleeding, Crohn’s disease, and small bowel tumors. (Figures 76.1–76.3). The entire small bowel can be visualized in a noninvasive manner using capsule endoscopy. The patency capsule is useful to confirm the patency of the gastrointestinal tract prior to administration of the capsule in patients with a suspected obstruction or stricture (Figure 76.4). Therapeutic management of small bowel lesions is now possible with deep enteroscopy techniques, including balloon‐assisted enteroscopy and spiral enteroscopy. Each of these devices has unique advantages and disadvantages that should be taken into consideration during selection of the appropriate modality. Capsule endoscopy and deep enteroscopy techniques are often considered as complementary tests, and utilized together in the evaluation of suspected small bowel disorders.

The images in this chapter illustrate the clinical usefulness of small bowel endoscopic modalities in the evaluation of patients with vascular lesions (Videos 76.1–76.3), inflammatory lesions (Figures 76.5 and 76.11), celiac sprue (Figure 76.6), polyps (Figures 76.7, 76.8, 76.10), and tumors (Figure 76.9).