Diagnostic colonoscopy

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Last modified 21/04/2015

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CHAPTER 4 Diagnostic colonoscopy

Summary

1 Anatomy

The colon is an elastic tube that extends from the rectum to the ileocecal valve and whose normal mucosa is pale-pink in color. The submucosal vascular network is visible, as are the rather large submucosal veins.

The colon comprises mobile segments (Fig. 1) (cecum, transverse colon, sigmoid colon) whose length depends on the size of the mesocolon, which attaches these segments to the posterior abdominal wall and the fixed segments (ascending colon, hepatic flexure, descending colon, rectum). The splenic flexure is partially attached by the phrenocolic ligament, the length and rigidity of which enable it to descend and become rounded on insertion of a colonoscope.

However, there are numerous anatomic variations resulting from the absence of mesorectal stickiness during gestation, which in turn induces variable mobility in the ascending and descending colon. In some cases, the cecum is incompletely rotated (cecum recurvatum).

The rectum is 12–15 cm long beginning from the anal margin. It is the shape of an elongated ampulla and is segmented by three or four mucosal folds (valves of Houston). The sigmoid varies in length, depending on the length of its mesocolon. The colonic lumen and haustrations in the descending or sigmoid colon are generally circular (Fig. 2). The splenic flexure exhibits a blue area that is attributable to the impression of the spleen. The lumen of the transverse colon is triangular (Fig. 3).

The indentation of the liver at the hepatic flexure can be recognized by its bluish color but note that this may also be visible from the descending colon or in the middle of the transverse colon. The hepatic flexure is easily confused with the cecal pole (one of the lips of the ileocecal valve may be confused with the thickened fold viewed tangentially above a flexure). The only reliable reference points are the terminal ileum, ileocecal valve and the appendicular orifice.

The internal aspect of the cecal pole, which typically exhibits a ‘crow’s foot’ shape, is the point of convergence of the three longitudinal bands of colonic muscle that extend to the appendicular orifice, which generally takes the form of a very narrow slit. An operated appendix looks the same, except that the stump has been buried and may resemble a polyp (can be biopsied but not resected).

The ileocecal valve is 5 cm above the cecal pole, on the medial wall of the right colon, usually on the left side of the colonoscopic field of vision. The valve takes the form of a transversally elongated mouth and is generally situated on the margin of one of the crow’s foot folds. The orifice of the ileocecal valve can rarely be viewed right away as it is normally located on the upper lip. Once the lower and upper lips of the ileocecal valve have been identified, it is possible to enter its orifice and examine the terminal ileum, where the submucosal vascular network is far more visible than in the colon. In children and adolescents, Peyer’s patches are often observed in the terminal ileum, where they constitute 2–3 mm white or translucent sessile protrusions and villi are also seen.

2 Indications for colonoscopy (TC)

These are general indications but specific guidelines exist in many countries and may vary. Readers should be familiar with the guidelines of the country in which they are practicing. References to some of these guidelines can be found elsewhere in this text. The following are the guidelines from the Société Française d’Endoscopie Digestive (SFED).

5 Preparation of the examination room (Box 3)

6 Handling the colonoscope

The endoscopist may work seated or standing, but must be in a comfortable position to keep the instrument as straight as possible.

Colonoscopy is performed by a single endoscopist who holds the control handles in their left hand (insufflation, aspiration, washing with the index and middle fingers, lever for up/down angulation between the thumb and index finger). The right hand advances or withdraws the apparatus, and introduces instruments into the biopsy channel. As it advances, the lubricated colonoscope is held between the thumb and index finger (Fig. 4).

6.1 General principles

The instrument should be directed at the areas in shadow (Fig. 6A) and towards the center of the arcs formed by the folds so as to advance in the direction of the lumen (Fig. 6B).

6.2 Bowel preparation score

The Ottawa bowel preparation quality score is determined by scoring the right, mid and left colon as well as the score for the quantity of fluid within the entire colon and adding the four scores together (Table 1), the range being 0-14.

Table 1 Ottawa bowel preparation quality score

  Score
Score right (R), mid (M) and left (L) colon separately (quality of preparation)  
No liquid 0
Minimal liquid, no suction required 1
Suction required to see mucosa 2
Wash and suction 3
Solid stool, not washable 4
Score the entire colon (overall quantity of fluid)  
Minimal 0
Moderate 1
Large 2
Total score: R + M + L + Fluid = __ / 14