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During endoscopy, experienced endoscopists occasionally find it difficult to identify where the lumen is due to factors such as acute angulations, numerous large diverticula, or inadequate colon preparation. Novice endoscopists, however, find factors such as red‐out (tip of the scope up against the colon wall), or inability to recognize clues to indicate the direction of the lumen, to be far more common. In the case where the lumen cannot be seen, it is always advisable for the trainee to slowly pull back on the scope until they are away from the wall and can identify clues to the direction of the lumen or until the lumen itself again becomes visible. In order to avoid perforation, a trainee should never continue pushing inward on the scope if the lumen is not visible.

Once away from the wall and red‐out corrected, there are a number of clues that can help the endoscopist identify the direction of the lumen. The most common is observing the direction of the haustral folds. The concave portions of the folds point in the direction of the lumen. The second is the use of shadows. When identifying a bright fold close to the scope and a dark shadow behind this, the lumen is often behind this fold. A third method that is often helpful in guiding the endoscopist is following the longitudinal ridge created by the tinea coli. The length of any of the three tinea coli will point in the direction the lumen is turning.

Similar to following the haustral folds as described above, ripples in the colon wall created by the circular muscle layer of the colon can also be used. When the colonoscope light reflects off of these arcuate ripples, steering the scope toward the concave portion of the arc should guide the endoscopist in the direction of the lumen.

All of these techniques can be used alone or in combination to help the endoscopist find their way to the cecum (Figure 6.16) (Video 6.3).