The small bowel is a difficult terrain to endoscopically examine due to its length, distensibility, and tortuosity. The length of the small bowel is highly variable and averages between 20 and 23 feet in the adult.¹,²,³,⁴ Small intestinal length is correlated with the height of the subject, and this variation may have an impact on enteroscopic procedural success.⁴,⁵ Beyond the ligament of Treitz, the small bowel becomes freely mobile along the mesentery. This topography, along with the small bowel’s active motility, poses challenges to the endoscopist seeking to navigate the depths of the small intestine.

For years, the available endoscopic tools limited small bowel evaluation to only its most proximal and distal segments. The large majority of the small bowel remained out of reach. In 1977, the Sonde enteroscope was introduced.⁶ This long flexible fiberoptic enteroscope was inserted nasally and passively propelled by intestinal peristalsis to the terminal ileum. From there, the endoscopist was able to examine the small bowel during withdrawal. The procedure was time consuming, uncomfortable for patients, and did not permit biopsy or therapeutic maneuvers. At this time, Sonde enteroscopy is of historical interest only and no longer has a role in the evaluation of small bowel disorders.

In the early 1980s, a colonoscope was used to access the jejunum from an oral approach, allowing for biopsies and other therapeutic interventions.⁷ Subsequently, dedicated push enteroscopes were developed, which permitted per-oral endoscopic access deeper into the winding and distensible small bowel.⁸ The midjejunum (150 cm beyond the pylorus) could now be reached. This depth of insertion could modestly be extended with use of an overtube, although the diagnostic yield remains similar.⁹,¹⁰,¹¹,¹² Push enteroscopy afforded the ability to perform diagnostic and therapeutic maneuvers available to the endoscopist via
traditional esophagogastroduodenoscopy and colonoscopy. Push enteroscopy increased the diagnostic yield for occult bleeding to at least 38%.¹³

Intraoperative endoscopy (IOE) has permitted access to the small bowel via a per-oral, per-rectal, or a surgical enterostomy approach. In this setting, an endoscopist works with a surgeon who subsequently telescopes the small bowel over the endoscope. Intraoperative enteroscopy permits examination of the entire length of the small bowel in over 90% of cases and has a diagnostic yield for bleeding of approximately 79%.¹⁴,¹⁵,¹⁶ It had previously been considered the gold standard for the diagnosis and management of small bowel conditions until recent years.

The noninvasive examination of the small bowel was revolutionized with the launch of video capsule endoscopy in 2001 following FDA approval.¹⁷ Small bowel findings identified on video capsule endoscopy, distal to the reach of push enteroscopy, could be more readily reached following the introduction of the double-balloon enteroscope in 2004.¹⁸,¹⁹ These new developments have increased the breadth of available tools in the endoscopic armamentarium to explore and treat small bowel disorders.

Despite these advances in endoscopic technology, the small bowel remains a challenging territory to endoscopically examine. Even though deeper insertion is possible with other tools, many small bowel pathologic findings are present within the proximal small bowel (duodenum to midjejunum) and remain within reach of push enteroscopy.²⁰ This chapter will focus on push enteroscopy evaluation of the small bowel.