Colonoscopy and flexible sigmoidoscopy
Colonoscopy and flexible sigmoidoscopy are techniques for visualizing the lumen of the large bowel. In expert hands, after appropriate explanation to the patient (which increases the chances of the procedure being well tolerated), bowel preparation, and (usually) some form of ‘conscious sedation’, then total colonoscopy is possible in 98 to 99% of cases in the absence of obstruction, a severely ulcerated colon, or other contraindication.
The indications for colonoscopy are wide and constantly expanding, and are likely to continue to do so until alternative less invasive techniques (‘virtual colonoscopy’ or genetic tests) are perfected. Common indications include patients with or requiring: (1) bleeding, anaemia, or occult blood loss; (2) chronic diarrhoea or known inflammatory bowel disease, which is accurately and easily assessed by endoscopy and biopsy; (3) polyps that can be removed endoscopically; (4) surveillance for cancer prevention. Abnormalities found by other diagnostic methods frequently turn out to be spurious when checked colonoscopically. Findings such as anastomotic strictures, typically after Crohn’s resection, are usually easily and effectively dilated by the endoscopist using a ‘through the scope’ balloon.
Flexible sigmoidoscopy is the best means of examining the bowel proximal to the rectosigmoid junction (the distal rectum and anal canal are well seen with a rigid instrument).
Colonoscopes range from 60 to 70 cm flexible sigmoidoscopes or thin, very flexible paediatric instruments also used in adults with fixation or stricturing, up to 165 cm colonoscopes with different flexibility characteristics and instrumentation channel sizes. Further technical improvements include higher resolution, zoom magnification, better control ergonomics, adjustable shaft flexibility, image enhancement, and magnetic imaging of shaft loops without fluoroscopy. Ultrasound colonoscopes, thin ultrasound probes for use with conventional instruments, and other more advanced technologies are available in specialist centres. Experimental efforts continue in the quest to develop self-propelled colonoscopes.
A large range of accessories can be introduced through the suction/instrumentation channel of a colonoscope, including biopsy or grasping forceps; washing, spraying or deflation tubes; cytology brushes; and injection needles. Therapeutic accessories include insulated forceps, polypectomy snares and retrieval devices, cutting wires, coagulating probes and argon plasma coagulating catheters, laser light guides, haemostatic clip and nylon loop applicators, dilating balloons, and metal stent introducers. Experimentation continues on the long-established principle of having an external ‘overtube’ in place beforehand which can be slid inwards to control problematic shaft looping. CO2 insufflation apparatus is also available which, since the gas is exhaled within 10 to 15 min, ensures that patients are not left distended after the procedure.
Cleaning and disinfection
As for all flexible endoscopes, skilled maintenance, regular checks, and meticulous cleaning are essential. All parts, including air, water, and instrumentation channels must be accessed during cleaning. It is not possible to sterilize a colonoscope but scrupulous mechanical cleaning and ‘high-level disinfection’ rapidly inactivate viral agents (including HIV and hepatitis B) and bacteria. However, mycobacterial spores require prolonged disinfection agents and may be present in AIDS patients, thus mandating invariably high standards of disinfection. Even with purpose-built washing machines, designed to perfuse the various channels of an endoscope, it can take up to an hour to clean and disinfect an instrument, so multiple colonoscopes are required to provide a routine service. Most accessories such as biopsy forceps or polypectomy snares are ‘single use’ disposables but any others require equally rigorous cleaning and autoclave sterilization or high-level disinfection. Prions are not removed by ‘high-level disinfection’ and hence instruments must be quarantined when they have been used for ‘invasive’ endoscopy, including biopsy, in a patient known to have or to be at risk of variant Creutzfeld–Jacobs disease (vCJD).
Psychological preparation of the patient should not be forgotten, since most of those scheduled for colonoscopy are apprehensive, whether through embarrassment, expected discomfort, or fear of colorectal cancer. Explanatory literature and a friendly telephone manner at the time of booking the exam can help a great deal. Equally, a warm and reassuring atmosphere on reception, while obtaining ‘informed consent’, and also during the procedure, can help transform colonoscopy from an ordeal into a reasonable and well-tolerated experience.
Flexible sigmoidoscopy preparation is normally by disposable enema (hypertonic phosphate or similar) given or self-administered 10 to 15 min before the procedure. Some patients prefer to avoid the indignity of an enema by taking full oral preparation and this is also advisable in any patient with a colon narrowed by pronounced diverticulosis or stricturing.
Full bowel preparation is usually the most unpleasant part of colonoscopy. Oral preparation must be preceded by dietary restrictions, which include stopping iron or constipating agents in the preceding days and a low-fibre diet (with no nuts, mushrooms, or iron-containing red wine) for at least 24 h.
Fluid overload is the commonest approach, usually achieved by ingestion of 3 to 4 litres of isotonic polyethylene glycol (PEG)–electrolyte solution, which avoids electrolyte losses. Various commercial PEG–electrolyte combinations exist, flavoured and packaged for posting. However, up to 10% of patients become nauseated, vomit, or become distended and stop drinking, which can result in poor preparation, especially in the proximal colon. A new low-volume 2-litre PEG preparation with ascorbic acid has recently been shown to be better tolerated and equally effective as the traditional 4-litre PEG preparation.
Purgative preparation is a very cheap and well-tolerated alternative, although a few individuals can suffer cramping, incontinence, or vasovagal reaction. After the dietary restrictions described above and senna or bisacodyl tablets on the afternoon before examination, a litre of isotonic osmotic laxative (commonly magnesium citrate) is drunk followed by other clear fluids to taste (including alcohol in moderation). Drinking continues up to the time of the procedure to avoid solidification in the proximal colon, which can result in adherent residue, difficult to flush or aspirate.
If there is any possibility that the patient is obstructed, full oral preparation is contraindicated because of the possibility of perforation; a smaller volume should be given, supplemented by enemas. In the presence of massive bleeding it may be preferable to proceed directly to colonoscopy, relying on the purgative effect of blood rather than wasting time on preparation. Nasal-tube lavage is an alternative compromise before emergency colonoscopy (with the angiography team alerted in case adequate views prove impossible).
There is surprisingly wide variation around the world in attitudes to colonoscopy. In certain countries with enough anaesthetists available (France, Australia) propofol anaesthesia is routinely employed. In others (Japan, China) and many institutions in Scandinavia, Germany or northern Italy, unsedated colonoscopy is the norm. Fashions and opinions change and the trend is to some form of medication.
‘Conscious sedation’ is offered to most patients in the United Kingdom, unless they are likely to be easy to examine (flexible sigmoidoscopy, previously easy examination, male gender, sigmoid resection, or stoma) or are motivated to manage without medication in order to leave rapidly afterwards or to drive home. To generalize, women have longer colons and are more likely to suffer without sedation. The unpleasant gnawing quality of ‘visceral pain’ caused by the inevitable stretching of colon or attachments during insertion is, in a tolerant patient, quite manageable for a few spells of 20 to 30 s. However, prolonged examinations or the sensitivity of patients with irritable bowel syndrome can be much helped by a minimal dose of a sedative–analgesic combination. Combining a low dose of benzodiazepine (typically, midazolam 2–3 mg, intravenously), with an opiate analgesic (e.g. fentanyl 25–100 μg, intravenously) reduces discomfort and anxiety and gives the patient a well-deserved feeling of euphoria. Low-level sedation of this kind does not inhibit conversation or the ability to complain of pain or to change position when necessary. Smaller doses should be given in older or sick patients but incremental larger doses (especially opiates) can be needed in apprehensive younger ones. Pulse oximetry monitoring and nasal oxygen is routine, resuscitation equipment, and reversal agents (flumazenil, naloxone) should be immediately accessible. Sedated patients should be accompanied home.
General anaesthesia is rarely needed and has the disadvantage that an unconscious patient cannot change position spontaneously, and also that removal of the warning given by pain may tend to more aggressive technique. However, physician-administered ‘propofol sedation’ is increasingly advocated in the United States of America and Germany and undoubtedly, in patients with particular reasons for anaesthesia, propofol gives excellent results with rapid recovery compared to high doses of conventional sedation.
Antispasmodics are decried by many on the basis that they are thought to elongate the colon and make insertion more difficult. Randomized trial shows this to be untrue and we routinely use hysocine N-butyl bromide to speed insertion and optimize the view.
The use of antibiotic prophylaxis prior to colonoscopy or flexible sigmoidoscopy to prevent endocarditis has been abandoned in new guidelines, even for patients previously considered at high risk, e.g. those with previous endocarditis, both in the United Kingdom and in the United States of America. Specific cases may still need prophylaxis, such as those with severe neutropenia.
Flexible sigmoidoscopy is the kindest and most logical means of examining proximal to the rectosigmoid junction (15 cm), whereas the distal rectum and anal canal are well, and in skilled hands often better, seen with a rigid instrument. In the presence of severe diverticular disease it may be impossible to reach even mid-sigmoid without expertise and a thin endoscope. After hysterectomy it may be cruel to examine without sedation. For this reason, although flexible sigmoidoscopy is both better tolerated and more accurate and effective than aggressive, rigid proctosigmoidoscopy, depth of insertion should be limited to what is tolerable by the individual patient. Some endoscopists mistakenly attempt to ‘reach the splenic flexure’ routinely. Without fluoroscopy or magnetic endoscope imaging, even expert endoscopists can be completely mistaken between sigmoid-descending junction and splenic flexure. At 60 cm of insertion the tip of the instrument can be anywhere between mid-sigmoid and hepatic flexure, and there are no positive localizing landmarks.
Insertion usually follows digital lubrication with jelly, the blunt tip of the instrument being inserted as the sphincters relax. Thereafter the instrument is coaxed in, as gently as possible, without haste or force, steering and ‘corkscrewing’ around bends with twisting movements. Forceful insertion with ‘red-out’, guesswork, or blind ‘push through’ are all avoided as far as possible. Any small polyps (up to 6 mm) that may be adenomas are normally snared at once, as they may be difficult to see on withdrawal (when the colon has been shortened and convoluted) or if left for subsequent colonoscopy. Because of the remote possibility of explosive gas concentrations after limited preparation, either repeated suction with air reinflation or use of CO2 should precede electrosurgery; alternatively, ‘cold snaring’ with physical removal of the polyp can be employed.
The use of flexible sigmoidoscopy for colorectal cancer screening is likely to increase following three recent, very large, randomized, population-based studies in the United Kingdom, Italy, and the United States of America reporting that one-off flexible sigmoidoscopy prevents left-sided colorectal cancer and colorectal cancer-related death. This level of evidence is not yet available for colonoscopy.
In expert hands, and in the absence of obstruction, a severely ulcerated colon, or other contraindication, total colonoscopy is possible in 98 to 99% of cases, with little sedation or suffering and virtually no complications. In less expert hands ‘total colonoscopy’ or ‘completion’ rates as low as 75% have been reported. The principal difference in technique between expert and inexpert is the ability, while keeping sufficient orientation for steering purposes, to pull back and crumple the segment of colon already traversed, and simultaneously straighten the way or bend ahead. The ideal is to keep the colonoscope as straight as possible and to pleat or ‘concertina’ the colon over it, avoiding the unnecessary loops and pain caused by pushing too hard or too long. The ideal is not always immediately achievable, so patience and determination—tempered by humanity—are essential qualities for the colonoscopist (see Video 184.108.40.206).
Video 220.127.116.11 Tri-split recording showing views of the endoscopist, the endoscopic luminal view, and the shape of the colonoscope by magnetic endoscope imaging. This latter technique uses magnetic coils in the endoscope to produce a three-dimensional representation of the shape of the colonoscope inside the patient without the need for fluoroscopy. Insertion through the sigmoid colon is shown with the formation and subsequent resolution of a common N-shaped loop demonstrated.
Paradoxically, a freely mobile colon, without the conventionally fixed segments in the descending and ascending parts, can be as difficult to traverse as one with adhesions. This is principally because atypical loops may form, sometimes uncontrollable until the instrument tip eventually reaches a fixed point, which gives a ‘hold’ and allows the shaft to be straightened back. Happily, this type of long and mobile colon, although a nightmare for the endoscopist, typically also has long attachments so that the patient experiences little discomfort.
From the point of view of the patient, colonoscope stretch discomfort is felt as ‘wind pain’, rapidly relieved as soon as the causative loop can be straightened. True overdistension is easily removed by aspiration. Further distress may be produced by the unpleasant illusion of incontinence when the body-warmed and lubricated shaft is withdrawn through the sensitive anal canal; it is kind to warn the patient of this phenomenon in advance, and to preserve decorum by aspirating any fluid found during insertion through the rectosigmoid.
Once the colonoscope has successfully passed into the descending colon and has been straightened back to remove sigmoid colon looping, it is likely that the rest of the insertion phase will be considerably easier. When the colonoscope shaft is straight it feels responsive and free, as do the angling controls: the more looped the colonoscope is, the more ‘snarled up’ everything becomes, and the more the patient suffers. Avoiding looping and responding to pain are the basis for successful, kind, and safe insertion. Good technique also minimizes instrument repair bills and maximizes accuracy and ease of targeting lesions, since a straight instrument handles better.
This practical philosophy underlies the reason for simple but effective ‘tricks of the trade’ such as position change. It is obvious that in left lateral position there will be pooling of any fluid in the left colon; the transverse colon will also tend to sag down and so make the splenic flexure more acute. It therefore follows that, where there is a poor view or difficulty in insertion, position change may improve matters (to supine or right lateral at the splenic, but back to left lateral again for the hepatic flexure). Adding only the simple principles of pulling back as often as possible to straighten each loop before tackling the next, avoiding overdistension to keep the bowel reasonably deflated and supple, and trying hand pressure from an assistant whenever an unavoidable loop may be accessible (sigmoid and transverse colon), the art of colonoscopy is explained. Insensitivity, impatience, or aggression results in the endoscopist being too muscular and tense to handle the shaft and controls sensitively, and so more likely to cause needless looping, pain, failure, and complications.
Contraindications, risks, and limitations
There are few contraindications to colonoscopy. It is, however, a relatively strong vasovagal assault with potential for arrhythmias and so is contraindicated for 2 to 3 months after myocardial infarction. The tip, shaft, and air pressure involved in insertion have potential to exacerbate any existing risk of perforation. Colonoscopy is thus contraindicated in the acute phase and 2 weeks after an episode of diverticulitis and in severe acute or deeply ulcerated colitis of any variety (ulcerative, Crohn’s, ischaemic or infective). Patients with acute localized or rebound tenderness of the abdomen, free air, or dilated colon on radiograph should not be submitted to colonoscopy without special reason, due consultation, and by an expert endoscopist—who may decide to abandon the procedure.
The risks of diagnostic colonoscopy, as implied above, are to a great extent related to the training, personality, and manual skills of the endoscopist. Regrettably, large-scale audit shows figures of around 1 perforation in 1500 to 2000 examinations, whereas in specialist centres complications are exceedingly rare. The overall figures can be justified by the avoidance of the morbidity and mortality of surgery. Therapy inevitably increases the likelihood of complications, principally bleeding but occasionally perforation after polypectomy or dilatation. Perforation may be actual (perhaps needing surgery) or threatened as the ‘postpolypectomy syndrome’ (managed conservatively with rest and antibiotics). Immediate bleeding can occur in around 1% of polypectomies but is usually easily stopped by submucosal adrenaline injection or by local electrocoagulation, clipping, or nylon loop application. Delayed haemorrhage can occur up to 10 to 14 days after removal or local coagulation of even small polyps; it is usually self-limiting, but can be substantial and require admission to hospital and transfusion. Aspirin is no longer considered a risk factor but antiplatelet agents such as clopidogrel should be stopped for a week before and after polypectomy. Anticoagulants should similarly be discontinued or special measures instituted.
The greatest causes of colonoscopy-related mortality (1 in 10 000 examinations) are patients referred (not always correctly) for surgery following endoscopic complications and deaths directly due to oversedation, usually in older people. There have been unnecessary deaths when an physician has persisted in conservative management without involving a surgeon in management of suspected perforation. Surgical fatalities or major morbidity have resulted in others found at operation to have sustained only a point perforation, which would clearly have sealed spontaneously. In managing suspected perforation, due consultation between endoscopist and an endoscopically aware, preferably laparoscopy oriented, surgeon is essential. The endoscopist should not be too proud to abandon an examination which is proving unreasonable, rather than to ‘flatten’ the patient with extra sedation; it is safer and kinder to change to CT colography (‘virtual colonoscopy’) to image the unexamined proximal colon during the same visit.
The major limitations of colonoscopy relate to the fact that it is dependent on manual skills and that tortuous, angulated, and haustrated colonic anatomy results in some blind spots for the endoscopist. Areas that the endoscopist sees are extremely accurately evaluated, with a resolution of less than 1 mm. The percentage of mucosa unseen is uncertain but is probably around 10 to 15% overall. The likelihood of larger and ‘significant’ lesions being missed is much lower than this because colonic neoplasms are usually protuberant. Paradoxically, pathology can be missed in the capacious distal rectum or the anal canal, which can be avoided by retroverting the endoscope and/or examining with a rigid proctoscope as well.
The indications for colonoscopy are wide and constantly expanding, and are likely to continue to do so until alternative less invasive techniques (virtual colonoscopy or genetic tests) are perfected. Where there is a shortage of endoscopic personnel, skill, or facilities it is possible to reduce the load of total colonoscopy by cross-referring for CT imaging. It is also possible to combine CT with prior flexible sigmoidoscopy on the same visit, on the basis that limited colonoscopy covers the highest yield area, which is also the most prone to missed diagnosis or overdiagnosis.
High-yield indications include patients with bleeding, anaemia, or occult blood loss. Persistent bleeding, especially if dark or mixed in with the stool, is of sinister import, although it may be due only to local mucosal traumatization in diverticular disease. Good clinicians may select out for sigmoidoscopy patients with obviously fresh bleeding on defecation or with spotting on toilet paper. However, the presence of blood in a patient aged 50 years or more (so at risk for colorectal neoplasia) is increasingly used as an excuse for the reassurance of a whole-colon screening examination. Of all patients with blood loss referred for colonoscopy, around 10% will have a ‘significant’ lesion, either a neoplastic polyp of 1 cm diameter or greater or malignancy. Colonoscopy is considered the investigation of choice for major bleeding, being readily available and offering immediate therapy and a high degree of diagnostic accuracy. Angiodysplasia, small ectatic vascular lesions in the proximal colon of older people with bleeding or anaemia, is relatively rare but is an example of a condition easily diagnosed and treated by colonoscopy.
Chronic diarrhoea or known inflammatory disease is accurately and easily assessed by endoscopy and biopsy. The terminal ileum can be accessed in more than 80% of cases by an experienced endoscopist. Endoscopic differential diagnosis between the focal or aphthoid ulcers with intervening normal mucosa in Crohn’s disease and the generally reddened surface of ulcerative colitis is easy and definitive in around 90% of cases. A few remain as ‘indeterminate colitis’ and differential diagnosis can be more difficult in severe or chronic cases. The possibility of infective colitis, including tuberculous or amoebic, must be borne in mind and extra specimens taken for microscopy and culture if in doubt. Biopsies typically show somewhat greater extent of inflammation than is visible to the eye, and so must be taken at intervals around the colon in any patient with bowel frequency to exclude ‘microscopic colitis’ or the related phenomenon of ‘collagenous colitis’. Chronic inflammatory disease affecting more than one-half of the colon carries an increased long-term risk of cancer or mucosal dysplastic (precancerous) change, and so indicates intermittent surveillance from 8 to 10 years after onset of symptoms. Ischaemic colitis, typically affecting a short segment around the splenic flexure, can show changes ranging from mild reddening to marked ulceration or even near gangrene.
There are low-yield indications for colonoscopy, where alternative investigations such as flexible sigmoidoscopy or ‘virtual colonoscopy’ may be justified. These include patients with simple constipation of long standing, bloating, left iliac fossa discomfort, or combinations of these symptoms suggesting ‘irritable bowel syndrome’. In many patients the extra accuracy and therapeutic potential of one-off colonoscopy may be justified. In older patients, however, the greater likelihood of diverticular disease and difficult (so more hazardous) colonoscopy is a disincentive compared to the rapidity and safety of scanning.
Polyps of almost any size can be removed endoscopically (see Video 18.104.22.168). Removal of very large sessile polyps in the distal rectum, for which transanal proctological management has been indicated, was traditionally not attempted by endoscopists but these are now manageable by endoscopic submucosal dissection (ESD), with superior view and greater safety. The place of laparoscopic removal or a combined approach for large sessile polyps in the proximal colon is in evolution. Otherwise even overtly malignant polyps or polypoid cancers with no adenoma present can be managed by endoscopy alone if complete removal is confirmed histologically (a margin of 1 mm between the limit of invasion and the plane of excision, and the tumour well or moderately differentiated). Around 5 to 10% of polyps will contain focal, high-grade dysplasia or invasive carcinoma but are endoscopically removable. Placing one or more Indian ink tattoos near a polypectomy site gives a permanent marker for endoscopic follow-up, or localizes it if surgery or laparoscopy become indicated by the histology results. Lasers were previously used for ablation of postpolypectomy remnants, but the alternative of argon plasma coagulation (APC) is cheaper, easier and safer.
Video 22.214.171.124 Example of a large (30 mm) sessile polyp in the transverse colon being resected by piecemeal endoscopic mucosal resection (EMR) after elevation with saline. Check examination 3 months later reveals no residual adenoma. Pathology confirmed tubulovillous adenoma with no invasion.
Cancer prevention or surveillance colonoscopy gives a good guarantee to the patient, even when negative, both because of the accuracy of colonoscopy and the generally slow time-course of development of colonic neoplasms. Follow-up at 3 to 5-year intervals after polypectomy yields further (usually small) adenomas in 30 to 50% of patients, especially those with three or more, or large, polyps on the initial examination. There is reasonable evidence to suggest that the incidence of colorectal cancer is significantly reduced by polypectomy and follow-up, but occasional breakthrough cancers occur and any bleeding or suggestive symptoms should be reported. Patients at genetic risk merit colonoscopic surveillance, especially those with a first-degree relative with colorectal cancer under 45 years of age, two or more affected first-degree relatives, or those assessed genetically as belonging to a hereditary non-polyposis colon cancer (HNPCC) family with autosomal dominant risk (see Chapter 14.15). Follow-up, ablating minute or ‘flat’ adenomas, is scheduled at intervals of 1 to 5 years according to perceived individual risk.
Abnormalities found on other diagnostic methods, when checked colonoscopically, frequently turn out to be spurious—presumably faecal. The majority of positive occult blood tests prove to be false positive for neoplasm. Other findings, such as anastomotic strictures, typically after Crohn’s resection, are usually easily and effectively dilated by the endoscopist using a ‘through the scope’ balloon. Even patients with typical malignant ‘applecore’ strictures should ideally have preoperative total colonoscopy to exclude other synchronous neoplasms, if necessary using a small-diameter instrument (sometimes a paediatric gastroscope). If this proves impossible, endoscopy should be rescheduled within 6 months after resection. Colonoscopy has effectively supplanted diagnostic laparotomy and avoids the numerous resections previously performed for diverticular disease when the radiologist ‘could not exclude the possibility of malignancy’—which the endoscopist can achieve in a few minutes.
Cost-effectiveness and relationship to other techniques
Flexible endoscopy seems superficially expensive and is demanding of professional time. However, modern colonoscopes are surprisingly robust and, properly handled and maintained, will perform thousands of examinations without expensive repairs.
Newer teaching methods, including use of computer simulation and imaging techniques that do not use X-rays, should help to improve manual skills and instrument handling and speed up the training and assessment of doctors or nurse practitioners performing colonoscopy or flexible sigmoidoscopy. There has been shown to be considerable variation between endoscopists in picking up adenomas, which translates into increases in interval cancers for poor detectors, hence quality assurance is essential..
Flexible endoscopy leaves only gas (air or CO2) in the colon, and can immediately be followed by scanning if incomplete. Total colonoscopy, its accuracy increasing to near microscopic levels with newer and more agile instruments, is likely to remain the diagnostic ‘gold standard’ for the foreseeable future. However, evolving newer methods such as virtual colonoscopy by scanning will be more acceptable to some patients and so have an invaluable role in screening and selection, in spite of their lack of tissue diagnosis or therapy. Since endoscopy can check an abnormal scan immediately, it is quite likely that colonoscopy will lose some of its present front-line diagnostic role. Nonetheless it is equally likely that requirements for colonoscopy will increase overall as population screening for colorectal cancer prevention becomes an accepted routine.
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