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Figure 6.22 Sigmoid loop. As the scope makes multiple turns in the sigmoid colon, advancing the scope frequently results in the force being transmitted laterally against the sigmoid walls (arrows) resulting in loop formation.

      (Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)

There are three main types of loops that develop in the sigmoid colon. The “alpha‐loop” is one of the most common and is termed this because the sigmoid is looped in a counterclockwise spiral in the shape of the Greek letter of its name (Figure 6.23) ( Video 6.5). The second most common loop is the “N‐loop” called this because it too is shaped like the letter of its name (Figure 6.24) ( Video 6.6). This loop follows and exaggerates the normal S‐shaped spiral of the sigmoid colon. Less common than these two is the “reverse alpha‐loop” that follows a similar spiral to the alpha‐loop but the more proximal sigmoid passes behind the more distal sigmoid (Figure 6.25) (Video 6.7). Which type of loop forms is likely due to variances in sigmoid anatomy? The method best suited for reduction of these sigmoid loops varies depending on the type of loop. In each of the loops, it is generally advisable to attempt to advance the scope beyond the splenic flexure, or other acute turn, if possible before attempting reduction. This allows the flexible portion of the scope tip to hook around this flexure and act as an anchor. This allows for greater direct force on the loop itself during reduction and torques maneuvers. Once anchored, the dials are held with the left thumb to prevent the scope tip from straightening out and slipping back into the descending colon. The two most common types of loops (alpha‐ and N‐loop) respond to slow scope withdrawal augmented by clockwise scope torque (Figures 6.23 and 6.24). During this maneuver, the tip of the scope may advance or simply remain motionless as the scope shaft is withdrawn. Clockwise torque and withdrawal of the shaft are continued until the scope tip begins to respond by starting to move backward in a one‐to‐one manner. This is evidence that the loop has been reduced. Torque is key to the maneuver as this will untwist the spiral nature of the sigmoid and create a straighter lumen if done correctly. The most common cause for failure of this technique is either failure to withdraw enough scope to re‐establish one‐to‐one motion or inadequate clockwise torque of the scope shaft during withdrawal. It is not uncommon to require 360° of torque or more during sigmoid reduction to adequately remove the spiral nature of this segment of the colon. Another cause of failure is the presence of a reverse alpha‐loop. Suspicion of this should arise if the usual clockwise maneuver repeatedly fails.

Figure 6.23 Alpha‐loop. One of the most common types of sigmoid loop formation is the alpha‐loop. This can be reduced with clockwise torque of the scope shaft as it is slowly pulled back. Once the loop is reduced, the scope shaft is again straight and can be readily advanced again.

      (Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)

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