[1] Esophagogastroduodenoscopy, also called upper endoscopy, gets as far as the first segment of the small bowel, the duodenum, but the next two, the jejunum and ileum, require other methods.
With the advent of the newer forms of enteroscopy, such as the double-balloon type, visualizing the entire tract is finally a practical reality in at least some cases, although it is still technically demanding.
Traditional gastroscopes can generally visualize the proximal and distal duodenum in the hands of experienced endoscopists but are limited due to the length of the instrument.
[1][2] Wireless capsule endoscopy has proven to be the endoscopic investigation of choice for visualization of the entire small bowel.
[1][2] Newer techniques, including single and double-balloon endoscopy have been developed to overcome some of these issues, but are limited by the length of the procedure, and the need for deep sedation or general anesthesia.