13.2.1 Anatomical Characteristics of the Small Intestine

The small intestine includes the duodenum, jejunum, and ileum, between the stomach and colon. It is located far from the mouth and anus, and is not fixed by peritoneal attachments with multiple complicated flexion points. This anatomical state makes it difficult to visualize the entire small intestine with conventional endoscopy.

13.2.2 Classification and Principles of Device-Assisted Enteroscopy

At the beginning of 21st century, the development and availability of device-assisted enteroscopy provided full access to the entire small intestine, for both diagnostic and therapeutic interventions. Device-assisted enteroscopy includes DBE (▶Fig. 13.1), SBE (▶Fig. 13.2), and spiral endoscopy (▶Fig. 13.3). Double- and single-balloon endoscopy are collectively known as balloon-assisted endoscopy. Although various devices are used, the mechanism is the same involving “folding redundant loops of the small intestine” (▶Fig. 13.4). This allows direct transmission of manipulation from the hand to the tip of endoscope even in the deep small intestine. Further, the working length of the endoscope does not have to be as long as the length of the intestine because device-assisted enteroscopy effectively shortens the intestine by repeat folding (“pleating”) of redundant loops. The endoscopes also have a working channel which enables biopsies, marking, endoscopic ultrasonography, and various therapeutic interventions such as balloon dilation and hemostasis.

13.2.3 Balloon-Assisted Enteroscopy (Double-Balloon Endoscopy/Single-Balloon Endoscopy)

Balloon-assisted endoscopy uses a soft overtube with a balloon at the tip. The overtube fully accommodates the working length of the endoscope. The balloon of the overtube wedges against the intestinal wall so that it can fold the small intestine enabling direct transfer of the endoscopic manipulation from the shaft to the tip of the endoscope. Balloon-assisted endoscopy includes DBE and SBE. DBE has two balloons, one at the tip of the endoscope and the other at the tip of the overtube, and SBE has a balloon only at the tip of the overtube. Yamamoto et al first developed and reported DBE in 2001, ¹ which was then released in 2003 by Fujifilm Corp. (Tokyo, Japan). At about the same time, capsule endoscopy was also reported and made available. ² In 2007, SBE was released by Olympus Corp. (Tokyo, Japan). The development and worldwide availability of balloon-assisted endoscopy has revolutionized the diagnosis and treatment of small intestinal diseases.

13.2.4 Spiral Endoscopy

Spiral endoscopy (Spiral Medical, LLC, Massachusetts, United States) utilizes a helical overtube that accommodates an endoscope (inner diameter is 9.8 mm and full length is 118 cm). The rotating overtube with protrusions hooks the fold, and the redundant small intestine is folded and fixed on the overtube. ³ Once the tip of the overtube passes the ligament of Treitz, the tip of endoscope passively moves forward by rotating the overtube without pushing the endoscope.

13.4.1 Hemostasis

Device-assisted enteroscopy enables endoscopic hemostasis in the distal small intestine, as far as the endoscope reaches. The most important and difficult issue is to identify the bleeding source distally in the small intestine. If a patient presents with obscure gastrointestinal bleeding, the examination of choice is probably a dynamic CT scan with contrast because of its low invasiveness and short procedure time. Based on the results of the CT scan, clinical manifestations, and conventional endoscopy, the appropriate device (capsule endoscope or device-assisted enteroscopy) is selected. If the CT scan shows extravasation, a mass lesion, wall thickening, or stricture, device-assisted enteroscopy is selected rather than capsule endoscopy. However, capsule endoscopy is used in patients with a negative CT scan. In case of overt obscure gastrointestinal bleeding, upper device-assisted enteroscopy is recommended. During upper enteroscopy, the appearance of bloody enteric contents indicates that the bleeding source is near because retrograde flow of intestinal contents usually does not occur in the small intestine. Therefore, a marking clip should be placed as a landmark where the bloody fluid is first seen. The operator can easily lose orientation in the distal small intestine without a landmark. The operator should then try to find the bleeding source around the area of the marking clip. If there is massive bleeding obscuring the visual field, use of the “gel immersion method” should be considered to obtain clear visualization and enable precise hemostasis. ⁶ When we investigate a patient with mid-gastrointestinal bleeding, the lumen of the small bowel is narrow and may be filled with blood. It is difficult to secure the visual field during enteroscopy for massive bleeding, because the injected water is rapidly mixed with fresh blood. Clear gel of an appropriate viscosity to prevent rapid mixing is injected through the accessory channel, instead of water. After gel injection, the bleeding source is clearly observed in the space occupied by the gel.

Bleeding sources in the small intestine are divided into three groups: vascular lesions, tumors/polyps, and ulcers/erosions. ⁷ Tumors/polyps and ulcers/erosions are usually treated by surgical or medical management after confirming the diagnosis by device-assisted enteroscopy. However, the mainstay of treatment for vascular lesions in the small intestine is endoscopic hemostasis using device-assisted enteroscopy. ⁸ Small intestinal vascular lesions are endoscopically classified by the Yano–Yamamoto classification based on the size and pulsatile nature of the lesion. ⁹ A lesion that is not pulsatile is considered to be a venous/capillary lesion, and is usually treated by argon plasma coagulation. Pulsatile vascular lesions are considered to be arterial in origin, and are usually treated by clip application.

13.4.2 Balloon Dilation

There are a number of diseases that cause small intesti nal strictures including Crohn’s disease, Behcet’s disease, nonspecific multiple small intestinal ulcerous disease, nonsteroidal anti-inflammatory drug–induced enteritis, ischemic enteritis, traumatic delayed-onset stricture, postoperative stricture, and scar formation after chemotherapy or radiotherapy. In these situations, device-assisted enteroscopy usually enables endoscopic balloon dilation as far as the endoscope reaches. Indications for balloon dilation include (1) fibrotic strictures with obstructive symptoms after medical treatment, (2) asymptomatic strictures with proximal bowel dilation shown by diagnostic imaging (fluoroscopic examination, computed tomography, and magnetic resonance imaging). Factors precluding balloon dilation include (1) a stricture that exceeds 50 mm in length, (2) a stricture with severe angulation, (3) a stricture with an active ulcer that seems to involve the muscularis layer, (4) a stricture with abscess formation, and (5) a stricture with a malignant appearance. ¹⁰

Endoscopic balloon dilation requires real-time fluoroscopic guidance. After reaching the stricture using device-assisted enteroscopy, endoscopic observation of the stricture and selective contrast studies are necessary to ascertain the indication for dilation. Using DBE, wedging, or inflating, the balloon at the tip of the endoscope prevents reflux of contrast media, resulting in clear visualization of the stricture. Next, the operator passes a soft guidewire through the stricture, and then introduces a through-the-scope dilation balloon. The location of the balloon is adjusted referring to real-time fluoroscopic images. The dilation time is usually about 1 minute.

Determining the correct balloon size is always difficult because the precise diameter of the stricture is difficult to estimate based on endoscopic imaging and selective contrast studies. The use of a transparent hood with calibration lines marked along the side may be used (▶Fig. 13.5). ¹¹ By wedging the stricture, one can measure the actual diameter. We recommend stepwise dilation to prevent iatrogenic perforation. Although 12-mm dilation is a typical goal for balloon dilation during the first session, 8- to 10-mm dilation may be appropriate in patients with severe strictures (< 6 mm in diameter before dilation). After the first session, additional repeat dilations are sometimes performed at 3- to 6-month intervals to attain 15-mm dilation as the final goal.