Introduction
Routine endoscopy is primarily limited to examination of the duodenal bulb and second portion of the duodenum, with an occasional glimpse of the third portion. With the availability of small-bowel enteroscopes and more recently of capsule technology, the entire small bowel can be visualized. The duodenal bulb appears as a small, round cavity with a finely granular appearance. At the superior duodenal angle, which marks the junction of the first and second portions, Kerckring’s valves, or the circular folds, become visible. In contrast with the bulb, the mucosa assumes a more granular and frequently whitish appearance. The ampulla occasionally may be identified on the medial wall, especially when prominent. The intimacy of the pancreas and biliary system to the duodenum may be reflected by endoscopic lesions resulting from diseases of pancreaticobiliary tree.
Duodenal disease is generally limited to the bulb, where inflammatory disorders, erosions, and ulcers are found. Neoplasms typically reside in the distal duodenum, jejunum, or ileum, and thus remain endoscopically hidden with routine endoscopy. If required, examination of the distal duodenum can be accomplished with a pediatric colonoscope or dedicated enteroscope. The anterior–posterior relationships in the duodenal bulb are important to understand, particularly when characterizing ulcer disease in the setting of gastrointestinal hemorrhage. The terminal ileum can be evaluated at the time of colonoscopy in most cases. In some situations, intubation of the terminal ileum should be routine; for example, when evaluating for Crohn’s disease or when finding fresh blood in the cecum in a patient with gastrointestinal bleeding. The identification of small-bowel lesions by capsule endoscopy may now be amenable to endoscopic therapy with the double-balloon endoscope.
Extrinsic neoplasm (cholangiocarcinoma, pancreatic carcinoma)
Periduodenal inflammatory process (e.g., pancreatitis)