- Email: [email protected]
Viewing the colon
Investigations
Viewing the colon
What’s new?
Brian P Saunders
• Magnetic endoscopic imaging enables visualization of the configuration of the scope within the patient in real time; this can reduce the incidence of instrument looping and improves manoeuvring of the instrument shaft • Variable-stiffness colonoscopes combine the flexibility of paediatric instruments for negotiation of the sigmoid colon with the ability to stiffen the insertion tube to prevent or control looping after straightening, thereby facilitating insertion through fixed or redundant segments of bowel
Disorders of the large bowel are common in the West. Colonic cancer is the second most common cause of cancer-related death; about 34,000 new cases are diagnosed each year in the UK. The incidence of inflammatory bowel disease (IBD), particularly Crohn’s disease, continues to increase. Effective imaging to diagnose and document the extent of disease is essential. Imaging may be indicated to define the cause of colonic symptoms or to screen patients at increased risk of colorectal cancer. Colonoscopy is the most important investigation, because it examines the entire colon and has both diagnostic and therapeutic capabilities.
• Virtual colonoscopy uses prone and supine helical thin-section CT scans that are rendered into a threedimensional sequence; this non-invasive technique may soon become an important new screening modality
50% of patients eventually die from the disease. However, most cancers develop from benign adenomatous polyps that may have been present for many years, and early detection and excision of adenomas (or early cancers) may therefore prevent cancer. Certain patients are known to be at greatly increased risk of colon cancer. Endoscopic screening (Table 1) is indicated in these individuals. Colonoscopy is widely accepted as the gold-standard investigation; however, debate continues regarding inclusion criteria and surveillance intervals. Endoscopic screening may also be warranted in the general (‘average-risk’) population. ‘One-off’ screening flexible sigmoidoscopy or colonoscopy at age 60 years has been proposed as the most cost-effective means of population screening. A large, prospective controlled trial is under way, with encouraging early results.
Indications Colonic symptoms – a full clinical history and examination are mandatory and help in selecting the most appropriate type of colonic imaging. Symptom overlap is considerable in colonic disease and imaging is often necessary to exclude serious pathology. New symptoms in patients aged over 45 years usually require investigation to exclude carcinoma. • Patients with diarrhoea, recent change in bowel habit, anaemia and dark-red rectal bleeding require pancolonic imaging. Colonoscopy is the investigation of choice when mucosal disease (neoplasia, IBD, angiodysplasia) is suspected. Sigmoidoscopy plus barium enema is an acceptable alternative in those with a change in bowel habit and suspected carcinoma. • Bright-red rectal bleeding, seen on the toilet paper or in the pan, is common and usually indicates local anal disease (e.g. haemorrhoids, fissure), though even bright-red bleeding may originate from the proximal colon. In younger patients, proctoscopy plus sigmoidoscopy may be sufficient, but older patients warrant pancolonic imaging. • Colicky lower abdominal pain relieved by defecation, parti cularly in younger patients, often indicates irritable bowel syndrome and usually requires only limited investigation. • Patients with symptoms suggestive of IBD or with inflammation extending beyond the reach of the rigid sigmoidoscope warrant full ileocolonoscopy to document the presence and extent of proximal disease. • Long-standing constipation has many causes, and special investigations such as transit studies, defecating proctography and anorectal physiology may be necessary. Endoscopic cancer screening – most patients with colon cancer present at an advanced stage when the prognosis is poor;
Proctoscopy Disposable plastic or autoclavable metal proctoscopes are quick and effective for examining the anal canal and distal rectum and should always be available in out-patient departments.
Colonoscopic surveillance intervals in patients at high risk of colorectal cancer • Adenoma • Cancer • Family history1 • Hereditary non-polyposis colorectal cancer • Long-standing /extensive colitis2
1–2-yearly
1Two first-degree relatives with cancer or one first-degree relative with cancer < 50 years of age (commencing 10 years before index case). 2Disease extending beyond the splenic flexure for more than 8 years; multiple biopsies taken looking for mucosal dysplasia.
Brian P Saunders MD FRCP is Consultant Gastroenterologist and Senior Lecturer in Endoscopy at St Mark’s Hospital, Harrow, UK.
THE FOUNDATION YEARS 3:1
3–5-yearly 3–5-yearly 5-yearly 1–3-yearly from age 25 years
Table 1
34
© 2006 Published by Elsevier Ltd.
Investigations
The proctoscope is inserted with the patient in the left lateral position. It is directed towards the umbilicus, the obturator is removed and a fibre-optic light source is connected. Examination is undertaken on slow withdrawal of the instrument. Haemorrhoids appear as reddish-blue swellings that bulge into the lumen and are easily accessible for injection, banding or infrared photocoagulation. Anal fissures and fistulas may also be seen, though pain may hamper the procedure and may necessitate examination under anaesthesia. Proctoscopy does not provide adequate views of the rectum. Sigmoidoscopy is therefore mandatory, even when anal pathology has been detected.
Sigmoidoscopy Almost all patients presenting with colonic symptoms should undergo rigid or flexible sigmoidoscopy as a standard part of out-patient examination. Rigid 25–30-cm sigmoidoscopes can be inserted into the distal sigmoid colon, but without bowel preparation views are usually limited to the rectum. Air is insufflated to aid insertion and spiral rotatory movements of the instrument during withdrawal help to maximize views of the rectal wall. Mucosal abnormalities such as polyps, cancer and inflammation can be detected; the diagnosis is confirmed with forceps biopsy. Asking the patient to strain down during withdrawal of the sigmoidoscope may also assess mucosal prolapse. Flexible sigmoidoscopy is a compromise between rigid sigmoidoscopy and colonoscopy; the length of colon that can be examined is at least three times greater than that with rigid sigmoidoscopy, but the complete colonic examination that is often required to exclude serious pathology is impossible. Flexible sigmoidoscopy may therefore need to be supplemented with barium enema or colonoscopy. Its primary role is as a rapid initial examination in patients with distal colonic symptoms, or to clarify the nature of a localized abnormality (e.g. sigmoid stricture seen on barium enema). About 60% of all colorectal neo-plasias are within the reach of the flexible sigmoidoscope, which is therefore potentially useful for colon cancer screening. Flexible sigmoidoscopy is an out-patient procedure and is usually performed without sedation in less than 10 minutes. High-throughput, rapid-access flexible sigmoidoscopy clinics have been developed. A potential disadvantage is the expense and complexity of the equipment compared with that needed for rigid sigmoidoscopy, and the need for comprehensive sterilization of the instruments and accessories. Furthermore, flexible sigmoidoscopy is technically more difficult than rigid sigmoidoscopy; at least 50 supervised examinations are necessary before competence is achieved. It also carries a slightly higher risk of complications than rigid sigmoidoscopy, though this risk is negligible with experienced operators. Following adequate bowel preparation (usually with a single phosphate enema), a 60-cm flexible sigmoidoscope can be passed reliably to the sigmoid/descending colon junction and often beyond. Sigmoid diverticular disease is common in Western countries; care is required during insertion through a diverticular segment because the bowel may be narrowed and fixed from serosal adhesions, and the multiple diverticular orifices can appear similar to the colonic lumen (Figure 1). After washing to
THE FOUNDATION YEARS 3:1
Figure 1 Sigmoid diverticular disease. At sigmoidoscopy, the multiple diverticular orifices can appear similar to the colonic lumen.
remove mucus and suctioning of retained fluid, good views can be obtained of the entire sigmoid and rectal mucosa. Because the tip of the instrument is flexible, there are no blind areas in the colon, and even the distal rectal ampulla can be imaged by tip retroflexion (Figure 2).
Figure 2 During sigmoidoscopy, a ‘J’ manoeuvre in the rectum enables clear visualization of the distal rectal ampulla.
35
© 2006 Published by Elsevier Ltd.
Investigations
to distend, particularly in the sigmoid colon where diverticular disease is often encountered. In many cases, colonoscopy is used to define an abnormality suspected on barium enema. Water-soluble (single-contrast) studies are seldom performed because mucosal definition is poorer than in double-contrast examinations. They are useful in defining fistulas, perforation or anastomotic leaks, and in diagnosis of Hirschsprung’s disease and megacolon. ‘Instant enema’ is a barium examination of an unprepared colon. It is useful when rapid assessment of the extent of active ulcerative colitis is required, and relies on the fact that formed residue is not present in areas of active inflammation.
Plain abdominal radiography A plain abdominal radiograph may provide useful information about faecal loading, colonic gas distribution and the presence of free peritoneal air. Colonic volvulus, pneumatosis coli and perforation have characteristic appearances. Plain abdominal radiography is invaluable in the assessment of severe IBD, in which lack of residue and abnormal haustration help to define the extent of inflammation, and serial radiographs document the development of toxic dilatation.
Barium enema Barium enema retains a role as an alternative to colonoscopy and is the investigation of choice for colonic fistulas (Figure 3). Sigmoidoscopy should always be performed before barium enema, because the distal rectal ampulla may not be imaged by the study and unrecognized rectal pathology may increase the small risk of perforation (1/25,000). Barium enema is contraindicated within 10 days of rigid sigmoidoscopic biopsy if large biopsy forceps are used, but appears to be safe if small cup forceps are used or biopsies are taken via a flexible sigmoidoscope. Colonic cleansing (see below) is mandatory. Sedation is not required. Double-contrast studies involve partial filling of the colon with barium, followed by insufflation of air to produce a thin film of barium over the entire colonic mucosal surface. The patient is rotated to ensure an even distribution of barium and an antispasmodic is administered to reduce colonic spasm. Filming in different orientations is performed such that overlying loops of bowel are viewed separately. Structural abnormalities are well defined and the anatomical ‘road map’ is useful to surgeons planning intervention. Smaller lesions and fine mucosal detail are less easily seen. Compared with colonoscopy, barium enema detects fewer polyps and is less sensitive in defining the extent and type of IBD. Significant abnormalities can be missed if the bowel fails
Colonoscopy Colonoscopy is the investigation of choice in the detection of disease affecting the colonic mucosa; gross abnormalities are immediately apparent, and small or flat lesions, which may be missed by barium enema, can be detected and their presence highlighted by dye-spray techniques (Figure 4). The colour view aids detection of the subtle mucosal changes seen in IBD (e.g. erythema, aphthous ulceration), and the ability to take biopsies, cytology brushings and bacteriological specimens further refines the accuracy of the technique. With an experienced operator, total colonoscopy can be achieved routinely in more than 95% of patients and ileal intubation in more than 90%. Examination of the colon is undertaken during insertion and more meticulously on withdrawal, ensuring as near complete mucosal inspection as possible. Equipment – a modern video-colonoscope contains a miniature video chip at its tip that relays detailed colour images of the colonic surface to a television monitor via an image processor. Hard-copy recording on video prints and videotape is possible, such that a permanent record of the examination can be made available to the referring clinician.
Figure 4 Flat adenoma with depressed centre, identified using indigocarmine 0.2% dye-spray.
Figure 3 Barium enema showing a colovesical fistula. Arrow, bladder.
THE FOUNDATION YEARS 3:1
36
© 2006 Published by Elsevier Ltd.
Investigations
Two new developments may greatly improve completion rates and improve patient comfort and safety. • Magnetic endoscope imaging uses low-power magnetic fields that track the colonoscope shaft as it is inserted into the patient, warning the endoscopist of endoscope looping and enabling rapid and accurate manoeuvres to straighten the endoscope shaft (Figure 5). • Variable-stiffness instruments allow the colonoscope shaft to be made more or less floppy according to the type of colonic anatomy encountered, facilitating insertion through fixed or redundant segments of bowel. These two developments are complementary; in the future, colonoscopes are likely to have both imaging and variablestiffness functions. Mucosal definition can be enhanced by the use of surface dyes such as indigocarmine 0.2%, and even greater microscopic detail can be obtained if a magnifying colonoscope is used. These provide views similar to those of a low-power light microscope (×100) and enable in vivo histological diagnosis. Preparation – before colonoscopy, patients must undergo adequate bowel preparation (usually with a combination of dietary restriction and laxatives). Various regimens are effective and it may be necessary to individualize preparation. Patients with diarrhoea or IBD often require full bowel preparation. Iron preparations stain stool black and should be stopped 10 days before colonoscopy. Aspirin and non-steroidal anti-inflammatory drugs should ideally be stopped 7 days before colonoscopy, and for 7 days afterwards if polypectomy is performed, to reduce the risk of bleeding. Patients taking warfarin for ‘low-risk’ indications (atrial fibrillation, venous thrombosis) can stop the drug 4 days before colonoscopy and restart soon afterwards; those taking it for ‘high-risk’ reasons (prosthetic heart valves) require conversion to heparin, which is stopped 4 hours before the examination. Antibiotic prophylaxis is indicated in patients with significant heart valve lesions, immunosuppressed patients and those receiving peritoneal dialysis. Most patients prefer some sedation
for colonoscopy. A combination of small doses of pethidine, 25–50 mg, and midazolam, 1–3 mg, is effective. Heavy sedation/ anaesthesia is not generally recommended or necessary. Pulse oximetry, supplemental oxygen and full resuscitation facilities should always be available. Therapeutic colonoscopy – the greatest advantage of colonoscopy is that it enables simultaneous diagnosis and therapy. Most colonic polyps and even some early cancers can be resected completely (Figures 6 and 7). Benign colonic strictures can be dilated with special ‘through-the-scope’ dilating balloons, and malignant strictures can be palliated using lasers or self-expanding metal stents. Postoperative ileus or pseudo-obstruction can be deflated and colonic volvulus usually de-rotated. Bleeding lesions can be electrocoagulated, strangulated or injected. The argon beamer is a new, inexpensive thermal device that provides controlled ablation of vascular lesions, polyps and cancers. Limitations • Colonoscopy is highly operator-dependent. A major disadvantage is the time required to gain technical competence. At least 100 supervised procedures are necessary to develop hand skills, though it is hoped that the development of computer simulation programs will accelerate training. • The inability of colonoscopy to identify the anatomical location of cancers accurately has been an argument in favour of barium enema. However, a permanent India ink tattoo enables identification on the serosal surface at laparotomy. • Serious complications can occur. Perforation is reported in about 1/2500 diagnostic examinations and in 1% of polypectomies. Because the colon is empty, some small perforations or near perforations can be managed conservatively with bed-rest and antibiotics, but surgical consultation is mandatory. Immediate bleeding after polypectomy (1.5% of procedures) can usually be stopped at the time of endoscopy by adrenaline injection or occlusion of the bleeding point with a metal clip delivered endoscopically. Delayed haemorrhage (1–2%) can occur up to 2 weeks after colonosopy and necessitates close observation in hospital. Bleeding often stops spontaneously without further intervention, but prolonged bleeding may require repeat colono-scopy with endoscopic treatment to the polypectomy base. As a last resort, embolization at angiography or laparotomy may be necessary.
CT In general, CT is of little use in predominantly mucosal diseases, because the resolution is insufficient to distinguish subtleties of diagnostic importance. CT is mainly used to detect extraluminal disease such as: • pericolic abscess (Crohn’s disease, diverticular disease, psoas) • postoperative pelvic collections • extracolonic tumours (e.g. metastases, ovarian, desmoid, endometriosis). CT is of limited use in local staging of colorectal cancer. Liver metastases can be seen, but lymph node involvement is poorly defined. Virtual colonoscopy is a new development combining spiral CT with advanced virtual reality computer software. CT volume data are reconstructed by computer to produce a representation of the colon that can be examined from the luminal surface in a ‘fly-through’ technique, producing views similar to those
Figure 5 Magnetic imager monitor showing a three-dimensional representation of the colonoscope shaft in anteroposterior and lateral views. The colonoscope shaft is looped in the sigmoid colon with the tip at the splenic flexure. Accurate abdominal hand pressure is being applied; the purple sphere represents the position of the endoscopy assistant’s hand over the apex of the loop.
THE FOUNDATION YEARS 3:1
37
© 2006 Published by Elsevier Ltd.
Investigations
a Before and b after piecemeal endoscopic snare resection of a large colonic polyp. Figure 6
obtained during conventional video-colonoscopy. In early clinical trials, virtual colonoscopy appears to be almost as accurate as conventional colonoscopy in detecting advanced cancers and large (>1 cm) polyps, but it is considerably less accurate in de-tecting small polyps (<1 cm) and flat lesions within the colon. Its role remains to be determined, but this non-invasive technique has much potential, particularly for colorectal cancer screening and in symptomatic patients in whom colonoscopy is likely to be technically difficult.
staging of rectal cancer. Colonic endoscopic ultrasonography has become more feasible with the introduction of ‘mini-probes’, which can be passed through the biopsy channel at colonoscopy to help define the endoscopic resectability of sessile colonic polyps and early cancers. MRI – pelvic MRI is the investigation of choice in complex perianal fistulas (Crohn’s disease) and helps in the planning of subsequent surgery. Virtual reality reconstruction of colonic MRI scans is being developed. Blood cell scans – radiolabelled WBC scans using indium-111 or technetium-99 are useful in assessing the extent and activity of IBD. Although endoscopy is more accurate in making an initial diagnosis, WBC scans are non-invasive and may be preferred when documenting disease relapses. RBC scans may give an approximate indication of the site of colonic bleeding, but colonoscopy or angiography is generally more accurate. ◆
Other techniques Ultrasonography – endo-anal ultrasonography is the imaging modality of choice in defining sphincter injuries and assessing perianal fistulas. Transrectal ultrasonography is useful in local
Further reading Atkin WS, CookCF, Cuzick J, et al. Single flexible sigmoidoscopy screening to prevent colorectal cancer: baseline findings of a UK multicentre randomised trial. Lancet 2002; 359: 1291–300. Brooker JC, Saunders BP, Shah SG, Williams CB. A new variable stiffness colonoscope makes colonoscopy easier – a randomised controlled trial. Gut 2000; 46: 801–5. Cairns S, Schofield JH. Guidelines for colorectal cancer screening in high risk groups. Gut 2002; 51(suppl 5): V1–2. Fenlon HM, Nunes DP, Schroy III PC, Barish MA, Clarke PD, Ferrucci JT. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 1999; 341: 1496–503. Shah SG, Brooker JC, Williams CB, Thapar C, Saunders BP. Effect of magnetic endoscope imaging on colonoscopy performance: a randomised controlled trial. Lancet 2000; 356: 1718–22.
Figure 7 Mucosal defect post-polypectomy after closure with three endoscopically placed metal Endoclips.
THE FOUNDATION YEARS 3:1
38
© 2006 Published by Elsevier Ltd.
Viewing the colon
What’s new?
Brian P Saunders
• Magnetic endoscopic imaging enables visualization of the configuration of the scope within the patient in real time; this can reduce the incidence of instrument looping and improves manoeuvring of the instrument shaft • Variable-stiffness colonoscopes combine the flexibility of paediatric instruments for negotiation of the sigmoid colon with the ability to stiffen the insertion tube to prevent or control looping after straightening, thereby facilitating insertion through fixed or redundant segments of bowel
Disorders of the large bowel are common in the West. Colonic cancer is the second most common cause of cancer-related death; about 34,000 new cases are diagnosed each year in the UK. The incidence of inflammatory bowel disease (IBD), particularly Crohn’s disease, continues to increase. Effective imaging to diagnose and document the extent of disease is essential. Imaging may be indicated to define the cause of colonic symptoms or to screen patients at increased risk of colorectal cancer. Colonoscopy is the most important investigation, because it examines the entire colon and has both diagnostic and therapeutic capabilities.
• Virtual colonoscopy uses prone and supine helical thin-section CT scans that are rendered into a threedimensional sequence; this non-invasive technique may soon become an important new screening modality
50% of patients eventually die from the disease. However, most cancers develop from benign adenomatous polyps that may have been present for many years, and early detection and excision of adenomas (or early cancers) may therefore prevent cancer. Certain patients are known to be at greatly increased risk of colon cancer. Endoscopic screening (Table 1) is indicated in these individuals. Colonoscopy is widely accepted as the gold-standard investigation; however, debate continues regarding inclusion criteria and surveillance intervals. Endoscopic screening may also be warranted in the general (‘average-risk’) population. ‘One-off’ screening flexible sigmoidoscopy or colonoscopy at age 60 years has been proposed as the most cost-effective means of population screening. A large, prospective controlled trial is under way, with encouraging early results.
Indications Colonic symptoms – a full clinical history and examination are mandatory and help in selecting the most appropriate type of colonic imaging. Symptom overlap is considerable in colonic disease and imaging is often necessary to exclude serious pathology. New symptoms in patients aged over 45 years usually require investigation to exclude carcinoma. • Patients with diarrhoea, recent change in bowel habit, anaemia and dark-red rectal bleeding require pancolonic imaging. Colonoscopy is the investigation of choice when mucosal disease (neoplasia, IBD, angiodysplasia) is suspected. Sigmoidoscopy plus barium enema is an acceptable alternative in those with a change in bowel habit and suspected carcinoma. • Bright-red rectal bleeding, seen on the toilet paper or in the pan, is common and usually indicates local anal disease (e.g. haemorrhoids, fissure), though even bright-red bleeding may originate from the proximal colon. In younger patients, proctoscopy plus sigmoidoscopy may be sufficient, but older patients warrant pancolonic imaging. • Colicky lower abdominal pain relieved by defecation, parti cularly in younger patients, often indicates irritable bowel syndrome and usually requires only limited investigation. • Patients with symptoms suggestive of IBD or with inflammation extending beyond the reach of the rigid sigmoidoscope warrant full ileocolonoscopy to document the presence and extent of proximal disease. • Long-standing constipation has many causes, and special investigations such as transit studies, defecating proctography and anorectal physiology may be necessary. Endoscopic cancer screening – most patients with colon cancer present at an advanced stage when the prognosis is poor;
Proctoscopy Disposable plastic or autoclavable metal proctoscopes are quick and effective for examining the anal canal and distal rectum and should always be available in out-patient departments.
Colonoscopic surveillance intervals in patients at high risk of colorectal cancer • Adenoma • Cancer • Family history1 • Hereditary non-polyposis colorectal cancer • Long-standing /extensive colitis2
1–2-yearly
1Two first-degree relatives with cancer or one first-degree relative with cancer < 50 years of age (commencing 10 years before index case). 2Disease extending beyond the splenic flexure for more than 8 years; multiple biopsies taken looking for mucosal dysplasia.
Brian P Saunders MD FRCP is Consultant Gastroenterologist and Senior Lecturer in Endoscopy at St Mark’s Hospital, Harrow, UK.
THE FOUNDATION YEARS 3:1
3–5-yearly 3–5-yearly 5-yearly 1–3-yearly from age 25 years
Table 1
34
© 2006 Published by Elsevier Ltd.
Investigations
The proctoscope is inserted with the patient in the left lateral position. It is directed towards the umbilicus, the obturator is removed and a fibre-optic light source is connected. Examination is undertaken on slow withdrawal of the instrument. Haemorrhoids appear as reddish-blue swellings that bulge into the lumen and are easily accessible for injection, banding or infrared photocoagulation. Anal fissures and fistulas may also be seen, though pain may hamper the procedure and may necessitate examination under anaesthesia. Proctoscopy does not provide adequate views of the rectum. Sigmoidoscopy is therefore mandatory, even when anal pathology has been detected.
Sigmoidoscopy Almost all patients presenting with colonic symptoms should undergo rigid or flexible sigmoidoscopy as a standard part of out-patient examination. Rigid 25–30-cm sigmoidoscopes can be inserted into the distal sigmoid colon, but without bowel preparation views are usually limited to the rectum. Air is insufflated to aid insertion and spiral rotatory movements of the instrument during withdrawal help to maximize views of the rectal wall. Mucosal abnormalities such as polyps, cancer and inflammation can be detected; the diagnosis is confirmed with forceps biopsy. Asking the patient to strain down during withdrawal of the sigmoidoscope may also assess mucosal prolapse. Flexible sigmoidoscopy is a compromise between rigid sigmoidoscopy and colonoscopy; the length of colon that can be examined is at least three times greater than that with rigid sigmoidoscopy, but the complete colonic examination that is often required to exclude serious pathology is impossible. Flexible sigmoidoscopy may therefore need to be supplemented with barium enema or colonoscopy. Its primary role is as a rapid initial examination in patients with distal colonic symptoms, or to clarify the nature of a localized abnormality (e.g. sigmoid stricture seen on barium enema). About 60% of all colorectal neo-plasias are within the reach of the flexible sigmoidoscope, which is therefore potentially useful for colon cancer screening. Flexible sigmoidoscopy is an out-patient procedure and is usually performed without sedation in less than 10 minutes. High-throughput, rapid-access flexible sigmoidoscopy clinics have been developed. A potential disadvantage is the expense and complexity of the equipment compared with that needed for rigid sigmoidoscopy, and the need for comprehensive sterilization of the instruments and accessories. Furthermore, flexible sigmoidoscopy is technically more difficult than rigid sigmoidoscopy; at least 50 supervised examinations are necessary before competence is achieved. It also carries a slightly higher risk of complications than rigid sigmoidoscopy, though this risk is negligible with experienced operators. Following adequate bowel preparation (usually with a single phosphate enema), a 60-cm flexible sigmoidoscope can be passed reliably to the sigmoid/descending colon junction and often beyond. Sigmoid diverticular disease is common in Western countries; care is required during insertion through a diverticular segment because the bowel may be narrowed and fixed from serosal adhesions, and the multiple diverticular orifices can appear similar to the colonic lumen (Figure 1). After washing to
THE FOUNDATION YEARS 3:1
Figure 1 Sigmoid diverticular disease. At sigmoidoscopy, the multiple diverticular orifices can appear similar to the colonic lumen.
remove mucus and suctioning of retained fluid, good views can be obtained of the entire sigmoid and rectal mucosa. Because the tip of the instrument is flexible, there are no blind areas in the colon, and even the distal rectal ampulla can be imaged by tip retroflexion (Figure 2).
Figure 2 During sigmoidoscopy, a ‘J’ manoeuvre in the rectum enables clear visualization of the distal rectal ampulla.
35
© 2006 Published by Elsevier Ltd.
Investigations
to distend, particularly in the sigmoid colon where diverticular disease is often encountered. In many cases, colonoscopy is used to define an abnormality suspected on barium enema. Water-soluble (single-contrast) studies are seldom performed because mucosal definition is poorer than in double-contrast examinations. They are useful in defining fistulas, perforation or anastomotic leaks, and in diagnosis of Hirschsprung’s disease and megacolon. ‘Instant enema’ is a barium examination of an unprepared colon. It is useful when rapid assessment of the extent of active ulcerative colitis is required, and relies on the fact that formed residue is not present in areas of active inflammation.
Plain abdominal radiography A plain abdominal radiograph may provide useful information about faecal loading, colonic gas distribution and the presence of free peritoneal air. Colonic volvulus, pneumatosis coli and perforation have characteristic appearances. Plain abdominal radiography is invaluable in the assessment of severe IBD, in which lack of residue and abnormal haustration help to define the extent of inflammation, and serial radiographs document the development of toxic dilatation.
Barium enema Barium enema retains a role as an alternative to colonoscopy and is the investigation of choice for colonic fistulas (Figure 3). Sigmoidoscopy should always be performed before barium enema, because the distal rectal ampulla may not be imaged by the study and unrecognized rectal pathology may increase the small risk of perforation (1/25,000). Barium enema is contraindicated within 10 days of rigid sigmoidoscopic biopsy if large biopsy forceps are used, but appears to be safe if small cup forceps are used or biopsies are taken via a flexible sigmoidoscope. Colonic cleansing (see below) is mandatory. Sedation is not required. Double-contrast studies involve partial filling of the colon with barium, followed by insufflation of air to produce a thin film of barium over the entire colonic mucosal surface. The patient is rotated to ensure an even distribution of barium and an antispasmodic is administered to reduce colonic spasm. Filming in different orientations is performed such that overlying loops of bowel are viewed separately. Structural abnormalities are well defined and the anatomical ‘road map’ is useful to surgeons planning intervention. Smaller lesions and fine mucosal detail are less easily seen. Compared with colonoscopy, barium enema detects fewer polyps and is less sensitive in defining the extent and type of IBD. Significant abnormalities can be missed if the bowel fails
Colonoscopy Colonoscopy is the investigation of choice in the detection of disease affecting the colonic mucosa; gross abnormalities are immediately apparent, and small or flat lesions, which may be missed by barium enema, can be detected and their presence highlighted by dye-spray techniques (Figure 4). The colour view aids detection of the subtle mucosal changes seen in IBD (e.g. erythema, aphthous ulceration), and the ability to take biopsies, cytology brushings and bacteriological specimens further refines the accuracy of the technique. With an experienced operator, total colonoscopy can be achieved routinely in more than 95% of patients and ileal intubation in more than 90%. Examination of the colon is undertaken during insertion and more meticulously on withdrawal, ensuring as near complete mucosal inspection as possible. Equipment – a modern video-colonoscope contains a miniature video chip at its tip that relays detailed colour images of the colonic surface to a television monitor via an image processor. Hard-copy recording on video prints and videotape is possible, such that a permanent record of the examination can be made available to the referring clinician.
Figure 4 Flat adenoma with depressed centre, identified using indigocarmine 0.2% dye-spray.
Figure 3 Barium enema showing a colovesical fistula. Arrow, bladder.
THE FOUNDATION YEARS 3:1
36
© 2006 Published by Elsevier Ltd.
Investigations
Two new developments may greatly improve completion rates and improve patient comfort and safety. • Magnetic endoscope imaging uses low-power magnetic fields that track the colonoscope shaft as it is inserted into the patient, warning the endoscopist of endoscope looping and enabling rapid and accurate manoeuvres to straighten the endoscope shaft (Figure 5). • Variable-stiffness instruments allow the colonoscope shaft to be made more or less floppy according to the type of colonic anatomy encountered, facilitating insertion through fixed or redundant segments of bowel. These two developments are complementary; in the future, colonoscopes are likely to have both imaging and variablestiffness functions. Mucosal definition can be enhanced by the use of surface dyes such as indigocarmine 0.2%, and even greater microscopic detail can be obtained if a magnifying colonoscope is used. These provide views similar to those of a low-power light microscope (×100) and enable in vivo histological diagnosis. Preparation – before colonoscopy, patients must undergo adequate bowel preparation (usually with a combination of dietary restriction and laxatives). Various regimens are effective and it may be necessary to individualize preparation. Patients with diarrhoea or IBD often require full bowel preparation. Iron preparations stain stool black and should be stopped 10 days before colonoscopy. Aspirin and non-steroidal anti-inflammatory drugs should ideally be stopped 7 days before colonoscopy, and for 7 days afterwards if polypectomy is performed, to reduce the risk of bleeding. Patients taking warfarin for ‘low-risk’ indications (atrial fibrillation, venous thrombosis) can stop the drug 4 days before colonoscopy and restart soon afterwards; those taking it for ‘high-risk’ reasons (prosthetic heart valves) require conversion to heparin, which is stopped 4 hours before the examination. Antibiotic prophylaxis is indicated in patients with significant heart valve lesions, immunosuppressed patients and those receiving peritoneal dialysis. Most patients prefer some sedation
for colonoscopy. A combination of small doses of pethidine, 25–50 mg, and midazolam, 1–3 mg, is effective. Heavy sedation/ anaesthesia is not generally recommended or necessary. Pulse oximetry, supplemental oxygen and full resuscitation facilities should always be available. Therapeutic colonoscopy – the greatest advantage of colonoscopy is that it enables simultaneous diagnosis and therapy. Most colonic polyps and even some early cancers can be resected completely (Figures 6 and 7). Benign colonic strictures can be dilated with special ‘through-the-scope’ dilating balloons, and malignant strictures can be palliated using lasers or self-expanding metal stents. Postoperative ileus or pseudo-obstruction can be deflated and colonic volvulus usually de-rotated. Bleeding lesions can be electrocoagulated, strangulated or injected. The argon beamer is a new, inexpensive thermal device that provides controlled ablation of vascular lesions, polyps and cancers. Limitations • Colonoscopy is highly operator-dependent. A major disadvantage is the time required to gain technical competence. At least 100 supervised procedures are necessary to develop hand skills, though it is hoped that the development of computer simulation programs will accelerate training. • The inability of colonoscopy to identify the anatomical location of cancers accurately has been an argument in favour of barium enema. However, a permanent India ink tattoo enables identification on the serosal surface at laparotomy. • Serious complications can occur. Perforation is reported in about 1/2500 diagnostic examinations and in 1% of polypectomies. Because the colon is empty, some small perforations or near perforations can be managed conservatively with bed-rest and antibiotics, but surgical consultation is mandatory. Immediate bleeding after polypectomy (1.5% of procedures) can usually be stopped at the time of endoscopy by adrenaline injection or occlusion of the bleeding point with a metal clip delivered endoscopically. Delayed haemorrhage (1–2%) can occur up to 2 weeks after colonosopy and necessitates close observation in hospital. Bleeding often stops spontaneously without further intervention, but prolonged bleeding may require repeat colono-scopy with endoscopic treatment to the polypectomy base. As a last resort, embolization at angiography or laparotomy may be necessary.
CT In general, CT is of little use in predominantly mucosal diseases, because the resolution is insufficient to distinguish subtleties of diagnostic importance. CT is mainly used to detect extraluminal disease such as: • pericolic abscess (Crohn’s disease, diverticular disease, psoas) • postoperative pelvic collections • extracolonic tumours (e.g. metastases, ovarian, desmoid, endometriosis). CT is of limited use in local staging of colorectal cancer. Liver metastases can be seen, but lymph node involvement is poorly defined. Virtual colonoscopy is a new development combining spiral CT with advanced virtual reality computer software. CT volume data are reconstructed by computer to produce a representation of the colon that can be examined from the luminal surface in a ‘fly-through’ technique, producing views similar to those
Figure 5 Magnetic imager monitor showing a three-dimensional representation of the colonoscope shaft in anteroposterior and lateral views. The colonoscope shaft is looped in the sigmoid colon with the tip at the splenic flexure. Accurate abdominal hand pressure is being applied; the purple sphere represents the position of the endoscopy assistant’s hand over the apex of the loop.
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Investigations
a Before and b after piecemeal endoscopic snare resection of a large colonic polyp. Figure 6
obtained during conventional video-colonoscopy. In early clinical trials, virtual colonoscopy appears to be almost as accurate as conventional colonoscopy in detecting advanced cancers and large (>1 cm) polyps, but it is considerably less accurate in de-tecting small polyps (<1 cm) and flat lesions within the colon. Its role remains to be determined, but this non-invasive technique has much potential, particularly for colorectal cancer screening and in symptomatic patients in whom colonoscopy is likely to be technically difficult.
staging of rectal cancer. Colonic endoscopic ultrasonography has become more feasible with the introduction of ‘mini-probes’, which can be passed through the biopsy channel at colonoscopy to help define the endoscopic resectability of sessile colonic polyps and early cancers. MRI – pelvic MRI is the investigation of choice in complex perianal fistulas (Crohn’s disease) and helps in the planning of subsequent surgery. Virtual reality reconstruction of colonic MRI scans is being developed. Blood cell scans – radiolabelled WBC scans using indium-111 or technetium-99 are useful in assessing the extent and activity of IBD. Although endoscopy is more accurate in making an initial diagnosis, WBC scans are non-invasive and may be preferred when documenting disease relapses. RBC scans may give an approximate indication of the site of colonic bleeding, but colonoscopy or angiography is generally more accurate. ◆
Other techniques Ultrasonography – endo-anal ultrasonography is the imaging modality of choice in defining sphincter injuries and assessing perianal fistulas. Transrectal ultrasonography is useful in local
Further reading Atkin WS, CookCF, Cuzick J, et al. Single flexible sigmoidoscopy screening to prevent colorectal cancer: baseline findings of a UK multicentre randomised trial. Lancet 2002; 359: 1291–300. Brooker JC, Saunders BP, Shah SG, Williams CB. A new variable stiffness colonoscope makes colonoscopy easier – a randomised controlled trial. Gut 2000; 46: 801–5. Cairns S, Schofield JH. Guidelines for colorectal cancer screening in high risk groups. Gut 2002; 51(suppl 5): V1–2. Fenlon HM, Nunes DP, Schroy III PC, Barish MA, Clarke PD, Ferrucci JT. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 1999; 341: 1496–503. Shah SG, Brooker JC, Williams CB, Thapar C, Saunders BP. Effect of magnetic endoscope imaging on colonoscopy performance: a randomised controlled trial. Lancet 2000; 356: 1718–22.
Figure 7 Mucosal defect post-polypectomy after closure with three endoscopically placed metal Endoclips.
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