CHAPTER 4 Diagnostic colonoscopy
Key Points
1 Anatomy
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.
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).
2 Indications for colonoscopy (TC)
2.1 Patients at average risk of colorectal cancer (CRC)*
2.2 Surveillance of asymptomatic patients at high risk of CRC
2.3 Surveillance of asymptomatic patients at very high risk of CRC
Box 1 Amsterdam II criteria for HNPCC
2.4 Surveillance of patients after resection of one or more colonic polyps
5 Preparation of the examination room (Box 3)
Box 3 The minimum equipment required for a colonoscopy room
5.1 Setting up and testing endoscopes
5.2 Setting up and testing additional equipment
6 Handling the colonoscope
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
Clinical Tips
Loop management
How do I know if I have a loop?
Suspect a loop if there is loss of one-to-one movement as you advance the colonoscope.
How do I reduce a loop?
The endoscope is torqued clockwise or in rare cases anticlockwise and then withdrawn.
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.
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 |
7 Examination technique
7.1 Preparation of the colon
Various preparations are available including: