Head or tail: the orientation of the small bowel capsule endoscope movement in the small bowel.

Background And Aims: The diagnostic accuracy of capsule endoscopy has been suggested to be influenced by the direction of the passage in the intestine. It is currently unknown if a head-first or a tail-first orientation are equally common during the descent through the small bowel. The aim of the study was to identify the orientation of the capsule along the migration through the small bowel.

Methods: Thirty capsule endoscopies were reviewed by an experienced observer. The direction of the passage through the pylorus and the ileoceccal valve was recorded for all the examinations. In addition, detailed review of the passage of the capsule in different segments of the small bowel was undertaken for all the capsules.

Results: The capsule was significantly more likely to pass the pylorus head-first compared to tail-first (25 and 5 out of 30, respectively, OR 5, 95% CI 65-94%, P < 0.001). In 28/30 studies, the capsule exited the ileoceccal valve head-first (OR-14, 95% CI 77-99%, P < 0.001). In an immersion experiment, uneven distribution of weight of the capsule body was demonstrated with the head part (camera tip) being lighter than the tail part.

Conclusions: The capsule endoscope usually passes through the pylorus and subsequent segments of the small bowel head-first. This observation suggests that the intestinal peristaltic physiology drives symmetrical bodies with their light part first. The principle of intestinal orientation by weight distribution may bear implications for capsules' design in the future.