Diagnostic colonoscopy

  • Summary

  • Introduction 101

  • 1

    Anatomy 101

  • 2

    Indications for colonoscopy (TC) 103

  • 3

    Contraindications 104

  • 4

    Equipment 104

  • 5

    Preparation of the examination room 104

  • 6

    Handling the colonoscope 104

  • 7

    Examination technique 105

  • 8

    Colonoscopy in inflammatory bowel disease 114

  • 9

    Complications of colonoscopy 115

  • 10

    Colonoscopy in children 118

  • 11

    Images 119

Key Points

  • High quality colonic preparation is essential.

  • Good technique is the key to allowing a rapid, complete examination of the colon.

  • The colonoscope should be advanced under visual control.

  • The colonoscope should be shortened frequently to ensure a short, straight endoscope.

  • Abdominal palpation and patient position changes are useful adjuncts.

  • Confirmation that the cecum has been reached should be made by identifying the ileocecal valve, appendix or entering the ileum and visualizing the small bowel.

  • Withdrawing the colonoscope should take a minimum of 6 minutes.

  • Retroflex gently in the rectum to avoid missing distal lesions.

  • Audit of colonoscopy outcomes should be performed regularly.


Optical colonoscopy is the gold standard method for examining the colon, is widely available, and offers the potential for biopsy and/or therapy during the same procedure. It is commonly performed for the evaluation of patients with lower GI symptoms and for screening/surveillance in people at risk of colorectal cancer. While colonoscopy has been an established technique for over 30 years, it can be technically difficult and is associated with a small but real risk of major complications. For these reasons, a good, careful technique, combined with a sound knowledge of polypectomy procedures is essential.


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.

Figure 1

Mobile colonic segments: cecum; transverse colon; sigmoid colon.

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 ).

Figure 2

Circular haustrations in the descending and sigmoid colon.

Figure 3

Triangular haustrations in the transverse colon.

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.

Postoperative colonic anatomy

The most prevalent types of colonic surgery are left hemicolectomy (anastomosis between the rectum and transverse colon), right hemicolectomy (anastomosis between the small intestine and transverse colon), subtotal colectomy (anastomosis between the ileum and rectum), and total colectomy with ileo-anal anastomosis. Anastomoses involving the small intestine, colon or rectum can either be end-to-side or end-to-end. Hence, it is necessary to be able to recognize the cul-de-sac and withdraw the endoscope in order to progress in the right direction. In cases of colostomy, colonoscopy can be performed via the stoma.

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).

Patients at average risk of colorectal cancer (CRC) *

* Defined as the average population risk.

  • Asymptomatic patients with a positive occult blood test (performed as part of a screening program, not on an individual basis)

  • Patients with abdominal pain associated with a change in bowel habit to looser for >6 weeks

    • Over the age of 50

    • Under the age of 50, if there is no response to symptomatic treatment

  • Patients with overt rectal bleeding

    • Repeated episodes of dark red bleeding, irrespective of age

    • Repeated isolated episodes of bright red bleeding in patients over 50 (flexible sigmoidoscopy or TC in patients under 50)

    • Profuse bleeding, as soon as the patient’s condition allows

  • Patients with symptomatic diverticulosis

  • TC is contraindicated in suspected acute diverticulitis, but should be undertaken at a later date (~6 weeks) if surgery is being considered or the diagnosis is in doubt

  • Patients with endocarditis caused by Streptococcus bovis or group D streptococci.

Surveillance of asymptomatic patients at high risk of CRC

  • Patients with a family history of CRC with a 1st-degree relative under 60 or several 1st-degree relatives with CRC:

    • TC at age 45 or 5 years younger than the age at diagnosis of the index case; if he/she was under 50 then TC at 5 and 10 years

    • For adenoma including non-advanced forms: follow-up colonoscopy at 3 years

  • Family history of colonic adenoma in a 1st-degree relative under 60:

    • TC at the age of 45 or 5 years younger than the age at diagnosis of the index case; if he/she was under 50, then TC at 5 and 10 years.

  • After surgery for colorectal cancer:

    • Incomplete colonic examination before surgery: TC at 6 months

    • Complete colonic examination before surgery: TC at 2–3 years then at 7–8 years

  • Patients with acromegaly:

    • At diagnosis, then depending on the findings. If normal, every 5 years until biochemical evidence of ‘cure’.

Surveillance of asymptomatic patients at very high risk of CRC

  • FAP (familial adenomatous polyposis) (see Ch. 1.11, Box 4 )

    • Member of a family with FAP: flexible sigmoidoscopy annually from the age 10–12 years

    • Member of a family with attenuated FAP: TC annually from the age of 30

    • FAP after colectomy: flexible sigmoidoscopy annually.

  • Hereditary non-polyposis colon cancer (HNPCC)

    • Member of a family with HNPCC: TC every other year from the age of 20–25

    • HNPCC after surgery: TC every other year

  • Juvenile polyposis (JP) family member: TC every 2–3 years from the age of 10–15

  • Peutz–Jeghers syndrome family member: TC every 2–3 years from the age of 18

  • Inflammatory bowel disease: pancolitis (> 10 years) or left-side colitis (> 15 years): TC every 2 (pancolitis) to 3 years (left-side colitis) and biopsies every 10 cm. Recent studies recommend routine use of indigo carmine or methylene blue chromoendoscopy with fewer, targeted biopsies of subtle abnormalities of colonic crypts or vessel pattern.

Box 1

Amsterdam II criteria for HNPCC

  • Three or more relatives with HNPCC associated cancers (colorectal cancer, endometrial cancer, small bowel, ureter, or renal pelvis), one of whom is a 1st-degree relative to the other two.

  • At least two generations must be affected.

  • One individual from the family must have been diagnosed with one or more cancers before the age of 50.

  • FAP must be excluded.

Surveillance of patients after resection of one or more colonic polyps

  • Hyperplastic polyps (size ≥1 cm, ≥5 in number, location in the proximal colon with a family history of hyperplastic polyposis): TC at 5, and 15 years

  • Low-risk adenomas (V3) or advanced adenomas (size ≥1 cm, ≥25% villous component, high-grade dysplasia (HGD) or in situ carcinoma) or V4.1/V4.2 adenomas:

    • Incomplete resection: TC at 3 months

    • Complete resection: advanced adenoma or ≥3 in number, or a family history of CRC; TC at 3, 8, 13, and 23 years

    • Complete resection: non-advanced adenoma, <3 in number and no family history of CRC; TC at 5, 10, and 20 years

  • Malignancy in an adenoma(V4.3, V4.4, V5, ‘polyp-cancers’)

    • Incomplete resection (V4.3, V4.4): TC at 3 months then at 3 years if nothing at 3 months

    • Complete resection (V4.3/4.4): TC at 3 years

    • Complete resection (V5): TC at 3 months if patient does not undergo colectomy.

Box 2

Vienna classification of gastrointestinal epithelial neoplasia and superficial gastrointestinal cancers

  • Category V1: negative for neoplasia.

  • Category V2: indefinite for neoplasia.

  • Category V3: low-grade neoplasia (LGIN).

  • Category V4: high-grade neoplasia (HGIN).

    • V4.1: high-grade dysplasia.

    • V4.2: in situ (non-invasive) carcinoma.

    • V4.3: suspicious for invasive carcinoma.

    • V4.4: intramucosal carcinoma.

  • Category V5: submucosal invasion by carcinoma.


  • Colonic perforation

  • Peritonitis

  • Acute cardiorespiratory failure

  • Recent myocardial infarction

  • Recent colonic surgery

  • Major aneurysm of the abdominal aorta or its branches.


The standard, multipurpose colonoscope used routinely measures 130 cm in length. The long colonoscope (170 cm) is more fragile, more expensive and less practical. Flexible sigmoidoscopes (60 cm long) are also available but are less useful, except in young adults with bright red rectal bleeding, or bloody diarrhea.

The more flexible pediatric colonoscope (130 cm long, 11 mm in diameter) is used in children from the age of 2 years upwards. It may be useful in adults for passing through strictures or in patients with a narrow, tortuous or acutely angulated sigmoid colon.

The following accessories are required: cold biopsy forceps, hot biopsy forceps, foreign body forceps, tripod grasper forceps, polypectomy snares, lavage catheter, injection needles, endoscopic clips, detachable loops dilating balloons, polyp retrieval (‘Roth’) nets, fixative containers.

Preparation of the examination room ( Box 3 )

Box 3

The minimum equipment required for a colonoscopy room

  • 1 cold light source.

  • 1 video processor.

  • 1 or more television monitors. These should ideally be high definition.

  • 1 bottle full of sterile water for irrigation.

  • 1 diathermy unit.

  • 1 argon plasma coagulation (APC) generator.

  • Additional imaging equipment: DVD recorder and discs; computer.

  • There should be at least four videocolonoscopes for one room to allow for cleaning, disinfection, maintenance and repair.

  • CO 2 insufflator.

  • Powered washing pump to clear adherent fecal matter.

Setting up and testing endoscopes

  • Set up the video colonoscope on the console

  • Check that the colonoscope is working properly (angulation, aspiration, insufflation, clear image)

  • Check the connections with the monitor, the printer and the image capturing equipment

  • Test the white balance for any endoscopes that still require this function

  • Check the image storage equipment, computer switched on, patient data entered.

Setting up and testing additional equipment

  • Suction bottle and connections: (single use disposable)

  • Examination couch: correctly insulated with a disposable protective covering and cot sides to prevent falls

  • Instrument trolley with labeled drawers or tiers containing all the instruments. It must be carefully checked before each examination and should match the type of examination

  • Accessories

  • Dyes and tattoos: to detect, delineate and mark small mucosal lesions (flat polyps, etc.)

    • 0.2% indigo carmine. It should be ready for use in a 50 mL syringe; colitis surveillance requires 150–200 mL, so it is useful to make it up in a bag of 0.9% saline

    • 0.5 or 0.7% methylene blue

    • Pure carbon black (‘Spot’, GI Supply Inc., Camp Hill, PA, USA) can be used to mark the site of a lesion before surgery, or for marking where a polyp was removed so that the area can easily be identified during subsequent screening colonoscopy. Sterile India ink suspension is an alternative but has been associated with immunological reactions

  • Anti-foaming agent (simethicone)

  • Lavage catheter

  • Disposable gloves

  • Gauze swabs

  • Lubricant for rectal examination and for lubricating the colonoscope

  • Washing equipment: sterile water, 50 mL syringes, connector tubing, and power wash pump.

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 ).

Figure 4

The lubricated endoscope is held between the thumb and index finger of the right hand with a compress.

General principles

  • The parts of the colonoscope that have not been introduced into the patient should be kept straight and not allowed to form loops.

  • Avoid excess air insufflation. Excessive air is uncomfortable for the patient as well as distending the proximal colon, which can make reaching the cecum more difficult.

  • Advance gently under visual control, avoiding the formation of loops by reducing them as they occur and preventing their reappearance by abdominal palpation (see Clinical Tips, below).

  • The instrument should be withdrawn to shorten the colon whenever possible. This is usually performed after navigating through the sigmoid, again after negotiating the splenic flexure, once or twice in the transverse colon and again once the instrument is in the ascending colon.

  • It is usually better to withdraw the instrument than to push it in blindly. If it is necessary to insert the colonoscope without a view of the lumen, the mucosal vascular network should pass in front of the lens. If the mucosa appears blanched, then there is excessive pressure on the colonic wall and a risk of perforation. Insertion must stop and the luminal view re-established.

  • Any polyp discovered during insertion should be removed because it may not be found during withdrawal.

  • Residues unlikely to obstruct the colonoscope should be aspirated during insertion so that the mucosa can be examined completely during withdrawal.

  • The procedure is usually performed with the patient lying in the left lateral position or supine, the latter usually when it is performed under general anesthesia. If there are problems advancing the colonoscope, consider moving the patient. In general, the following patient positions often facilitate scope passage if difficulty is encountered:

    • Rectosigmoid – supine or right lateral

    • Splenic flexure – right lateral

    • Hepatic flexure – supine or left lateral.

  • The lumen of the colon is at the center of the convergence of folds if the colon is not insufflated or in spasm ( Fig. 5 ).

    Figure 5

    The lumen of the colon is at the centre of the convergence of folds.

  • 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 ).

    Figure 6

    (A,B) The colonoscope should be directed at the areas in shadow and the concave area of the arcs formed by the folds.

  • On withdrawal, which is done slowly to examine the whole mucosa, it may be necessary to re-advance to see areas difficult to observe (beyond the ileocecal valve, hepatic flexure, splenic flexure, sigmoid colon and rectosigmoid junction, and the distal rectum) ( Fig. 7 ). Longer withdrawal times are associated with increased adenoma detection rates. Current recommendations suggest that the colonoscope should be withdrawn over at least 6 minute.

    Figure 7

    Blind areas difficult to observe: behind the ileocecal valve, hepatic flexure, splenic flexure, sigmoid colon and rectosigmoid junction, lower part of the rectum.

  • The report should specify whether the bowel preparation was adequate (to determine the reliability of the examination); any problems with advancing and the maneuvers used should also be noted. This may be useful in a subsequent examination.

Clinical Tips

Loop management

What is a loop?

A loop forms if the tip of the colonoscope does not advance at the same rate as the shaft during insertion. One-to-one movement is lost and paradoxical movement can be seen where the tip appears to fall backwards as the scope is inserted.

What types of loops are there?

  • Alpha loop ( Fig. 9 ) (see full discussion below).

  • Omega loop ( Fig. 10 ).

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.

How do I know if I have successfully reduced the loop?

Loops are reduced correctly when the tip of the endoscope advances during scope withdrawal. If the tip falls backwards, the loop reducing maneuver is incorrect and should be repeated with torque in the opposite direction.

Do I have to reduce every loop?

An alpha loop does not always have to be reduced. If the patient is comfortable and the endoscopist is making good progress, you can push through an alpha loop and then reduce it after you have passed the splenic flexure.

How do I stop it recurring?

Reduce the loop as described above. Once you have one-to-one movement, advance the scope with gentle clockwise torque and use abdominal pressure to keep the scope straight and to prevent the loop recurring. If it does recur, reduce the loop and apply abdominal pressure on another area.

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 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

Examination technique

Preparation of the colon

The colon must be scrupulously clean in order to perform reliable colonoscopy and polypectomy safely. Up to 23% of colonoscopies are reported to have inadequate preparation. This is associated with increased risk of missing polyps or small cancers, prolonged procedures and may increase the risk of complications. Preparation is carried out at home except for elderly, frail patients who may require hospitalization.

Various preparations are available including:

  • Macrogols: polyethylene glycol (PEG e.g. Klean-Prep, Moviprep). These are isosmotic and do not cause net shift of large amounts of fluid across the intestinal epithelium. They require large volumes of 2–4 L for efficacy and can be unpalatable. Dividing the dose may facilitate dosing, so that half is taken the night before and half on the morning of the procedure. Electrolyte shifts are rare.

  • Sodium phosphate (sodium dihydrogen phosphate, e.g. Fleet Phospho-Soda) is hyperosmotic and works by causing net secretion of large volumes of water into the intestinal tract. It is better tolerated than PEG solutions with equal or better cleansing. Hypovolemia, electrolyte disturbances and renal failure are more common with NaP in patients with risk factors (see Warning, below).

  • Sodium picosulphate and magnesium citrate (e.g. Picolax) in combination: picosulphate is metabolized in the gut and stimulates peristalsis. The ingested volume is low and bowel cleansing is usually adequate. Dehydration, electrolyte shifts, and renal failure are rare.

  • Magnesium carbonate and citric acid (e.g. Citramag) are low volume osmotic stimulants, mainly used for bowel preparation prior to barium enema or CT colonography.

In general, there is little to choose among them in terms of efficacy and all require clear, careful explanation to patients beforehand and full compliance if good results are to be achieved. Serious reports of major complications, particularly with sodium phosphate preparations, have recently led to many countries issuing safety notices regarding the use of bowel preparation in general and NaP in particular (see Warning and Table 2 ).

Mar 5, 2019 | Posted by in GASTOINESTINAL SURGERY | Comments Off on Diagnostic colonoscopy
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