SBE [3] (Fig. 3.3) is a simplified DBE system that omits the balloon at the tip of the scope. As it utilizes a similar overtube with a balloon to that in DBE, it can reach deep inside the small bowel while maintaining operability. As attachment of a tip balloon to the scope is unnecessary, SBE has the advantage of simpler and shorter preparation. However, as the scope tends to be pulled out while advancing the overtube and the holding force during retraction is weaker, SBE is reported to be inferior in terms of success rate of observation of the entire small bowel compared to DBE [4, 5]. Additionally, in selective contrast study as described below, the reflux of contrast agent cannot be prevented in SBE because of the lack of the balloon at the tip of the endoscope. Balloon-assisted endoscopy (BAE; balloon-assisted endoscopy) is a unifying terminology referring to both DBE and SBE.

In addition to BAE, SE [6] has been invented as another endoscope that can reach deep inside the small bowel. SE is a small-bowel endoscopy system (Fig. 3.4) comprising an overtube with a screw-like spiral projection at the distal end (Discovery Small Bowel: Spirus Medical, Inc.) and an endoscope fitted to the size of the overtube (inner diameter 9.8 mm, total length 118 cm). The spiral projection on the tip of the overtube is hooked into the folds of the small bowel and, by simple rotation of the overtube, the bowel is pleated over it. Once the tip of the overtube passes the Treitz ligament and is advanced into the jejunum, an assistant can advance the endoscope simply by rotating the overtube, without having to operate the body of the endoscope back and forth.

There are a few studies that directly compare BAE and SE [7–9]. While DBE is capable of inserting the endoscope deeper, the procedural time is shorter for SE; there is no significant difference in diagnosis rate and treatment rate for both systems. However, in a randomized comparative study (Messer/2012) that compared the success rate of observation of the entire small bowel, the reported observation rate among 13 subjects without previous surgery of the large or small bowel was 8% for the SE group and 92% for DBE group, demonstrating a significant difference. Additionally, for transanal insertion, SE’s capability of being inserted deep inside the small bowel is poor and its usefulness is limited for diagnosis and treatment of IBD, for which most lesions are in the ileum.

When a BAE pleats the intestine over the overtube with a balloon and shortens it, gas remaining inside the intestine may interrupt the retraction operation, much like an air spring. Recently, the usefulness of insufflation of carbon dioxide instead of air during endoscopy has been reported and become widely used, mainly in colonoscopy. Carbon dioxide gas tends to be absorbed by water and into the body at 100 times or more the speed of air; it is also excreted in exhaled air. This profile is useful particularly for BAE, as the tendency for carbon dioxide to leave the intestine more quickly means that it tends not to interrupt the retraction operation. Insufflation of carbon dioxide gas is now an essential part of BAE operation.

Selective contrast study, in which water-soluble contrast is injected from the forceps channel of the endoscope, is an effective procedure for examining areas that are unreachable by endoscope. However, particularly in IBD cases, deformation and stricture of the intestine can prevent the injected contrast from flowing ahead, frequently rendering evaluation impossible with a standard endoscope. Because dilation of the balloon at the tip of the scope can suppress the reflux of contrast agent, DBE can make contrast examination of the deep small bowel possible, even when there is deformation or stricture of the intestine. Information obtained from examination with water-soluble contrast is limited compared with contrast enteroclysis with barium, but if carbon dioxide gas is used for insufflation and the contrast agent is injected slowly after aspiration of remaining gas and then the contrast imaging is taken, sufficient information can be obtained to evaluate the presence and absence of stricture.