Colonoscopy

Colonoscopy is an important aid in diagnosis and management of patients with inflammatory bowel disease (IBD). This procedure, with multiple biopsies, is indicated when adequate data are not available from clinical, sigmoidoscopic or radiologic studiesand there is strong clinical suspicion of IBD. However, colonoscopy carries an increased risk of perforation when the bowel wall is inflamed and presents with ulcers and fistulae. Known or suspected severe inflammation is a relative contraindication to colonoscopy. Toxic megacolon is an absolute contraindication to endoscopy if performed only for diagnostic purpose because of the weakness of the colonic wall, which is paper thin [10]. Endoscopy monitoring to assess response to therapy has been evaluated by a randomised study in which patients were treated with steroids. In one group, steroid tapering was decided on following clinical remission; in the other group, the decision was based on endo-scopic findings. The conclusion was that colonoscopy was not necessary to decide when to taper steroids, as the two groups did equally well [11].

Colonoscopy evaluation of the extent of disease is also part of preoperative assessment in order to decide the extent of resection and define the segments free from disease. The ileocecal area is the most frequent site of the disease, accounting for about 70% of cases. Of these, 20-30% involved the colon only, and 40-55% had ileocolic disease [12]. Although considered peculiar of Crohn's colitis, rectal sparing is found in less than half of patients. When the rectum is involved, the disease begins at the rectosigmoid junction or appears with anorectal inflammation. The entire rectum is affected by the disease from 5% to 10%. Lesion progression, from aphthous to serpiginous ulcers, has a discontinuous and asymmetric course, with the inflamed mucosa typically presenting normal "skip areas" [13]. Segmental localisation of the disease has a high predictive value [ 14].

Other endoscopic features found during a colonoscopy include pseudopolyps, erosions and stenosis. A prospective study evaluated the incidence of different lesions found during a colonoscopy. All the patients were affected by Crohn's disease and underwent the procedure before beginning therapy. Endoscopy showed the following findings: 93% superficial erosions, 74% deep erosions, 48% mucosal oedema, 44% erythema, 41% pseudopolyps, 10% aphthous ulcers, 8% ulcerated stenosis and 2% nonulcerated stenosis [15].

Pseudopolyps represent regenerative epithelium and may include granulation tissue without prema-lignant potential. They are often multiple and bright, with a fragile surface that bleeds very easily when biopsies are taken. Endoscopic differential diagnosis with adenomas can be difficult, and only biopsy will provide definitive diagnosis [16]. They need to be resected if bleeding or causing obstruction, and polypectomy is performed in the same way as in the general population [17].

Colonoscopy allows direct investigation of strictures. Biopsies are mandatory to rule out stenoses caused by carcinoma. Malignant lesions are usually eccentric, rigid and may present nodules within the stricture or at its margins [18]. The colonoscope should go beyond the stenosis in order to carry out a thorough inspection, using a pediatric instrument if needed, avoiding the standard colonoscope to act as a dilator [19]. Endoscopic features may also have prognostic value, as reported by Allez and collaborators [20]. They found that patients with deep and extensive ulcerations of the colon are at higher risk of penetrating complications and undergoing surgery. Distribution of severe endoscopic lesions was the following: rectum 13%, sigmoid colon 77%, left colon 62%, transverse colon 51%, right colon 28%.

When disease involves the colon only, the main differential diagnosis is between Crohn's disease and ulcerative colitis (UC) (Table 1). Usually, the two entities can be differentiated endoscopically, and inflammation distribution can aid diagnosis. Crohn's colitis is more likely in the presence of skip areas or when the rectum is spared. In UC, the rectum may be spared by local treatment or when the proximal colon is more involved than the rectum during an acute severe attack [21]. Moreover, peculiar to Crohn's disease is the presence of deep linear ulcerations separated by areas of normal mucosa as well as terminal ileum involvement. Inflamed mucosa extends for more than a few centimeters, and ulcerations are present in this portion of the small intestine. Although the small bowel is not involved by UC, a few centimeters of inflamed mucosa without ulceration may be present in the terminal ileum (backwash ileitis) in 15-20 % of patients with pancolitis.

When extensive inflammation of the colon is present, differential diagnosis between Crohn's disease and UC may be very difficult. Patients presenting features of both diseases are considered to have indeter-

Table 1. Crohn's disease and ulcerative colitis: endoscopic differential diagnosis

Crohn's disease

Any portion of gastrointestinal tract

Often stenotic or ulcerated

Frequent

Sometimes

Rare

Asymmetric inflammation

Frequent Aphthoid/deep Frequent Frequent

Features

Distribution

Ileocecal valve

Lesions to terminal ileum

Lesions proximally to terminal ileum

Rectal involvement

Continuous colitis

Mucosal involvement

Segmental inflammation

Skip areas

Cobblestones-like areas

Ulcerations

Fistulas

Stenosis

Ulcerative colitis

Contiguous involvement of the colon starting from rectum

Without ulcerations

Backwash ileitis (15-20%)

Not present

95-100%

Circumferential inflammation

Rare

Shallow

Rare

Rare minate colitis, and at least 10% of patients who present with an IBD is regarded as having indeterminate colitis [22]. Usually, they are treated and monitored as are patients with UC unless signs of Crohn's disease develop. Other diseases that may resemble Crohn's disease are functional disorders (e.g. irritable bowel syndrome), immunomediated (e.g. connective tissue diseases), drug induced [(e.g. nonsteroidal anti-inflammatory drugs (NSAID)], vascular (e.g. intestinal ischaemia), neoplastic (e.g. carcinoma, lymphoma), infective or diverticular disease.

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