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Flexible endoscopy: lower gastrointestinal tract

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Abstract

Flexible endoscopy is particularly useful for examining the large intestine, and this can be performed by relatively inexperienced endoscopists. This chapter covers instruments, indications, patient preparation and positioning, procedure, biopsy collection, pathological conditions, postoperative care and complications.

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Figures

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6.1 Anatomical structure of the large intestine. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.2 For carrying out an endoscopic examination of the large intestine in both dogs and cats a forward-viewing endoscope should be selected, with an insertion tube length of at least 1 m (ideally 1.4 m) and an outside diameter of 7–9 mm. There must be a wash and air facility, and a biopsy channel of at least 2 mm diameter.
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6.4 Careful preparation of the large intestine is essential if the entire mucosal surface is to be thoroughly examined. The presence of faeces severely restricts the ability to carry out this examination.
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6.5 To aid intubation of the transverse and ascending colon, and to ensure that any residual fluid does not interfere with the endoscopy, the patient should be placed in left lateral recumbency. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.6 Once the endoscope has been advanced into the rectum, the lumen should be inflated with air. It should then be possible to visualize the descending colon extending in front of the endoscope. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.7 The mucosa of the colon should appear pale pink in colour and the submucosal blood vessels should be clearly visible through the thin mucosal layer.
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6.8 As the endoscope is advanced along the descending colon, eventually a ‘bend’ will be observed, which represents the flexure between the descending and transverse colon. This is a normal anatomical landmark, which will be observed on a second occasion as the endoscope reaches the flexure separating the transverse and ascending colon. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.9 The ascending colon is short and ends at the ileocaecocolic junction. The ileum appears as a raised red button-shaped structure while the caecum is a blind-ended sac.
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6.10 Careful selection of biopsy forceps will ensure crush artefact is reduced to a minimum. Forceps with a central spike (left) should not be used; forceps with fenestrated biopsy cups (right) should be selected.
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6.11 (a) Method of collecting biopsy samples from the colon. (b) The forceps should be advanced as near perpendicular to the mucosa as possible. This will ensure that a sample of good depth is collected. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.12 Structure of the colonic mucosa. = crypt openings; = lamina propria; = columnar epithelium; = crypt; = goblet cell. Drawn by S. J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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6.13 Lymphocytic–plasmacytic colitis results in thickening of the mucosa so submucosal blood vessels can no longer be seen. In many cases lymphoid hyperplasia will be observed as raised ‘doughnut’-shaped structures.
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6.14 Occasionally, lymphocytic–plasmacytic colitis may be severe. In such cases proliferative changes may be seen suggesting the possible presence of neoplasia. It is essential to collect biopsy samples for histopathology and not to overinterpret the visual changes.
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6.15 Eosinophilic colitis usually results in erosions and ulceration of the mucosa, which will also be friable and bleed readily. Submucosal bleeding may give the mucosa a red to purple coloration.
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6.16 Where granulomatous colitis is found, the majority of the colon will usually appear normal and only a small section of the colon will be affected. The lumen of the intestine may appear obstructed by marked mucosal thickening, and bleeding is not uncommon. The changes must be differentiated from neoplasia by examination of biopsy samples.
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6.17 Irritable bowel syndrome is difficult to diagnose as there are no visual or pathological changes present. However, at endoscopy the colon may be difficult to dilate and excessive amounts of mucus may be observed.
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6.18 Adenocarcinoma is an aggressive tumour that invades the lumen of the colon. The tumour will appear irregular and proliferative in appearance, may bleed easily and may appear very friable to touch. The remainder of the colon may be unaffected.
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6.19 Observation of an intussusception when carrying out large intestinal endoscopy is rare. However, when one is present, the ileum will appear as a normal pink colour filling the lumen of the colon, with no bleeding or ulceration in the majority of cases.
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6.20 Rectal adenomatous polyps can be diagnosed easily with the aid of endoscopy. They appear very similar to adenocarcinoma and must be differentiated by collecting and examining biopsy samples.
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6.21 Rectal strictures often appear as an obvious narrowing of the lumen, and a circumferential lip may prevent forward movement of the endoscope.
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6.22 A diverticulum can be seen at the 7 o’clock position in this view of the rectal mucosa in a dog.

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