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Overcoming the Sigma – Part 2

The long meso-sigmoid

Once passed the recto-sigmoid junction, if the endoscopist perceives to progress in a straight segment without feeling any tension on the control knobs and, especially, if the patient does not complain of any discomfort  or pain, it is likely that the scope has engaged into a sigmoid colon with a very long meso-sigmoid. This can take different shapes according to the technique of advancement, the position of the patients and the type of colonoscope (Fig. 22).


Fig. 22: radiologic appearance of a sigmoid colon with a long meso-sigmoid.

One of the possible shapes that a sigmoid colon with a long meso-sigmoid can take during the intubation phase is the so-called “αlpha-loop” (fig. 23); in this condition the colonoscope, whose tension is distributed over a wider parietal arch, can easily advance up to the descending colon, or even the transverse colon, particularly if the colonoscope is very flexible or of smaller caliber. Anywy, an experienced endoscopist feels a certain tension on the shaft of the scope and on the control knobs, and also perceives the progressive loss of the “one-to-one” effect. 

Fig. 23: a sigmoid colon with an “alpha-loop”. 

In the 2-hands technique (Fig. 24 A-B), when the colonoscope is engaged in an “alpha-loop”-shaped sigmoid, the endoscopist should progressively torque the shaft of the scope to the right (clockwise), and simultaneously withdraw the instrument until the tension on the control knobs disappears and the tip of the scope is free to move in the colonic lumen. 

Fig. 24 A-B: If the colonoscope is engaged in a regular sigmoid alpha loop (A), with the 2-hands technique the reduction of the loop is achieved by simultaneous retraction and clockwise rotation of the shaft of the colonoscope(B).

Sometimes the torque needed to straighten an α-loop requires a 360° rotation of the shaft and the handle; in this way the bends of the shaft are transferred to the segment of the scope that joins the handle to the light source (Fig. 25).

Fig. 25: Transfer of the curvature from the shaft to the segment of the scope interposed between the handle and the light source. 

If during the withdrawal maneuver, the tip of the colonoscope contextually goes back, it is possible that there is an “inverted alpha-loop, whose reduction requires an anti-clockwise torque with the right hand (Fig. 26)

Fig. 26 A-B: to reduce an inverted sigmoid alpha loop (A), an anti-clockwise rotation of the shaft of the colonoscope is needed (B).

In the 4-hands technique, the endoscopist achieves the same result combining a progressive withdrawal of the scope with a pronounced rotation of the chest to the right, moving the handle of the scope to the right side or to the left side, depending on the presence of a regular or an inverted “alpha loop” (Fig. 27 A-D).

Fig. 27 A-D: to straighten a regular sigmoid “α–loop” (A), withdrawal of the scope should be combined with a marked rotation of the chest to the right (B); in case of an inverted “α–loop”(C), the rotation of the chest is made to the left (D)..

The complete photographic sequence of this maneuver is reported in the chapter: The 4-hands intubation technique

When the maneuver is correctly performed, some 30 cm of instrument can be retrieved without any moving back of the tip of the scope, which instead slides automatically forward. The ideal condition to perform this maneuver is hooking the fold of the splenic flexure. With a regular sigmoid α–loop it is almost invariably possible to reach the splenic flexure; here the tip of the scope is angled toward the direction contrasting its retraction and the endoscopist begins to perform the maneuver (video 2). Once the scope has been straightened, before proceeding with the advancement, the endoscopist should stabilize the position achieved by rotations and contra-rotations of the handle to complete the telescoping of the sigmoid on the colonoscope and full aspiration of any excess air. 

Also when the  α–loop is inverted, the colonoscope can be pushed forward to hook the splenic flexure, and then start to the maneuver of withdrawal and anti-clockwise rotation (video 3).

The figure below shows the different types of α-loops that can occur during the intubation of the sigmoid colon and illustrates the combination of maneuvers required for their straightening (Fig. 28)


Fig. 28 : different shapes of sigmoid α-loops and combination of maneuvers (arrows) to perform for a correct straightening of the colonoscope: regular α-loop with right curve (upper left), with left curve (lower left); inverted α-loop with right curve (upper right), and with left curve (lower right).

Once passed the recto-sigmoid junction, if the meso-sigmoid is particularly long, , the colonoscope easily progresses for some 40-60 cm and then gets stuck into an acute angle beyond which it is not possible to proceed. In this situation the intubation has likely realized a the so-called long “N-loop”, with a very extended ascending portion of the sigmoid (S-top), and a much shorter descending portion inserting toward the left parietocolic gutter (Fig. 29).

Fig. 29: the shape of the sigmoid with the so-called long ‘N-loop’.

If the endoscopist “forces” the intubation, the tip of the scope does not move forward and the patients suffers intense pain. In fact, the insertion pressure increases the wide angle of the ascending portion of the sigmoid, without transmitting any effective energy to the advancement of the tip (Fig. 30).

Fig. 30: with a long ‘N loop’, forcing the progression with the tip of the scope engaged in the descending branch of the sigmoid, the ascending branch absorbs all the pushing force causing pain to the patient. 

To regain a chance for progression, first it is necessary to withdraw the colonoscope slowly, with the patient in the supine position. To maximize the straightening effect, the endoscopist will try to hook the fold of the sigmoid-descending angle during the retraction of the colonoscope (Fig. 31 A-D). 

Fig. 31: in the sigmoid with a long ‘N-loop’, pushing the shaft of the colonoscope does not result in any progression, but rather widens the sigmoid loop (A). Hooking the tip of the scope to the fold of the distal descending colon (B), it is possible to slowly withdraw the scope and progressively reduce the curvature of the sigmoid (C-D).

If a further retraction of  the shaft causes a moving back of the tip, then the maneuver has likely reduced the width of the parasite arch, and the sigmoid colon is now at least partially telescoped on the colonoscope. When the hooking is effective, the tip is released and the endoscopist rotates the chest to the right, to reduce at the minimum the parasite curve in the sigmoid, and possibly turning it around in axis with the lumen of the descending colon (Fig. 31 E). The simultaneous maximal air aspiration will contribute in reducing the length of the sigmoid colon (Fig. 31 F).

Fig. 31 E-F: the torque of the shaft of the scope to the right (E), turns around the parasite curve of the sigmoid, and helps to complete the telescoping of the sigmoid on the colonoscope (F).

To finish the maneuver, the nurse exerts a compression on the abdomen, searching the most favorable area, witnessed by the progression of the tip when the shaft in inserted (fig. 32).  

Fig. 32: the targeted abdominal compression prevents the parasite sigmoid curve to recur after the straightening maneuver

The endoscopist feels to have achieved the one-to-one effect and can now progress along the descending colon, regaining his/her position in front of the endoscopic table.

If the attempts at reducing the curvature length fail, it is possible to make a further attempt rotating the patient to the right lateral decubitus (Fig. 33 A-C)

Fig. 33: the right lateral decubitus of the patient, thanks to the gravity, modifies the angles of the recto-sigmoid and sigmoid-descending junctions. 

Fig. 33 B-C: with the patient in the left lateral decubitus (B) the angle of the recto-sigmoid junction (green circle) is wider than that of the sigmoid-descending colon (red circle). With the patient in the right lateral decubitus (C), the angle of the sigmoid-descending junction becomes wider (green circle), and also the angle of the splenic flexure (S) opens up due to the gravity that drags the transverse colon downward.

The change in the position of the patient takes advantage of the gravity to let the colon slide onto the tip of the scope and facilitate the intubation.

In some cases, an effective straightening of the  ‘N-loop’ is initially achieved, but the subsequent engagement of the tip in a very angulated splenic flexure causes the parasite curve to recur (Fig. 34)

Fig. 34: if, once a long ’N-loop’ has been straightened, ,the tip of the scope is engaged in a particularly angulated splenic flexure, the curvature of the sigmoid tends to recur.

Albeit rarely, in this condition the progression is impossible despite the adoption of different ancillary maneuvers (change of patient’s position, abdominal compression, use of the variable stiffness colonoscope, etc) and this is really a sticky, hard-to-solve situation. If the endoscopist is expert and has the adequate devices, one chance of progression is linked to the use of an ‘overtube’ on the colonoscope, that is cautiously slid inside the patient along the shaft after maximum straightening of the sigmoid (fig. 35).

Fig. 35: the use of an ‘Overtube’, though nowadays outdated with the modern variable stiffness colonoscopes,  may in highly selected cases help the progression instruments with a particularly flexible shaft. 

This maneuver should be performed under fluoroscopic guidance, to ensure that the recto-sigmoid angle is obtuse; when available, such control can be made with a magnetic 3D scope-guide system (UPD system by Olympus ) (Fig. 36).

Fig. 36: the magnetic 3D scope guide system (UPD system), enables the endoscopist to assess in real time the arrangement of the inside the colon, to verify the development of curves and to check the modalities of straightening.

Endoscopy Side Graphic

Endoscopy Side Graphic