CHAPTER 20 Endoscopy of the upper and lower gastrointestinal tract
‘Endoscopy’ simply refers to examining the inside of the body with a scope. Nowadays, we generally consider ‘endoscopy’ to be an examination of the gastrointestinal tract. Since the introduction of the flexible fiberoptic endoscopes in the 1960s, endoscopy has come a long way from the days of rigid sigmoidoscopy or rigid esophagoscopy. Modern endoscopes are used to carry out day-to-day diagnostic and therapeutic procedures of the gastrointestinal tract. For the purpose of this chapter, we will concentrate on flexible endoscopy.
Upper gastrointestinal tract (GI) endoscopy and lower gastrointestinal tract endoscopy means direct inspection of the esophagus, stomach, duodenum, small intestines and the colon using a flexible fiberoptic endoscope. A gastroscopy (aka esophago-gastroduodenoscopy or OGD) refers to the examination of the esophagus, stomach and duodenum, whereas enteroscopy refers to examination of the small intestines. Full examination of the colon to the cecum is known as colonoscopy, examination of just the left colon to the splenic flexure is known as flexible sigmoidoscopy.
Both endoscopy and fluoroscopy complement each other in the assessment of the GI tract. Gastroscopy is the investigation of choice for upper GI investigation and colonoscopy often follows radiological investigation. It could be argued that endoscopy would be preferable in every case as the patient could have both diagnosis and treatment in a single test. However, in many hospitals, endoscopy services are overstretched and a barium enema is often a good first line test in selected patients. Endoscopy also carries a risk of morbidity and even mortality as discussed below.
Most upper GI endoscopy is carried out by a forward looking gastroscope. This investigation will allow examination to and in some cases into the proximal jejunum. To examine the small bowel, an enteroscope (essentially a very long gastroscope) or capsule endoscopy is used. In practice, patients would usually have undergone prior fluoroscopic investigation by means of barium follow-through or enteroclysis.
To prepare for upper gastrointestinal endoscopy patients are asked not to eat or drink for 4–6 hours prior to the procedure. The procedure can be done under local anesthetic to the throat or under sedation. The gastroscope is passed via the mouth, through the cricopharyngeal sphincter and into the esophagus. Once intubation is achieved the examination of the esophagus, stomach and duodenum is relatively straightforward (Figures 20.3, 20.4 and 20.5, see color insert). There are several blind spots that merit special attention. The view of the esophageal mucosa is often lost at the point of passage through the sphincter and lesions can be missed. If this is suspected, the patient should undergo a barium swallow or a rigid esophagoscopy. Another potential blind spot is the superior part of the gastric antrum and angulus. It is important to retroflex the gastroscope in the antrum to gain a good view of this area.
Enteroscopy is used to examine mainly the proximal small bowel. This is a much more involved procedure than gastroscopy. Enteroscopy is indicated for diagnosis of small bowel diseases including obscure gastrointestinal bleeding, malabsorption, obtaining tissue biopsies following abnormal fluoroscopic studies as well as therapeutic procedures for treating small bowel bleeding or polyps.
Visualization of the lower bowel can be performed using a rigid or flexible endoscope. Rigid sigmoidoscopy and proctoscopy usually occur in the outpatient clinic. The Association of Coloproctology of Great Britain and Ireland recommends that a patient referred for barium enema should have had at least a rigid sigmoidoscopy prior to referral (Guidelines for Management of Colorectal Cancer, 2007). The reason for this is that lesions very low down in the rectum may be missed on barium enema but seen on proctoscopy or rigid sigmoidoscopy. A rigid examination is especially important in patients presenting with bright red rectal bleeding as common pathologies such as distal proctitis or hemorrhoids may not be demonstrated on barium enema.
Proctoscopy involves inserting a rigid instrument approximately 10 cm long into the distal rectum. No air insufflation is used but there is a light source attached giving good visualization of piles/mucosal prolapse but only limited views of the lower rectum. For full visualization of the rectum a rigid sigmoidoscope is used. This is a 25 cm long rigid tube connected to a light source with air insufflation to give a good luminal view. The word ‘sigmoidoscopy’ is actually a misnomer as it is difficult to negotiate the various mucosal folds required to enter the sigmoid with a rigid instrument. However, it is useful diagnostic tool and may influence the investigation subsequently chosen. For example, if a polyp is seen at rigid sigmoidoscopy, it is preferable to go straight to colonoscopy where a therapeutic procedure can be performed at the same time. Likewise, if distal colitis is seen, colonoscopy may be more appropriate than barium enema to determine extent and get a tissue diagnosis.
Flexible endoscopic examinations of the lower GI tract fall into two tests – flexible sigmoidoscopy and colonoscopy. Previously, there were separate endoscopes for each test but, in practice, a colonoscope is used for both. A colonoscope is a 160 cm long fiberoptic telescope that is inserted via the anus.