Introduction
Lower gastrointestinal (GI) endoscopy, either sigmoidoscopy or a colonoscopy with ileoscopy is useful in patients with inflammatory bowel disease (Table 1). Lower GI endoscopy helps in establishing a diagnosis especially when combined with mucosal biopsies, to assess severity of the disease, to assess the extent of the disease, to monitor and guide treatment strategies and to detect complications.

Diagnosis
For establishing the diagnosis of ulcerative colitis, a sigmoidoscopic exam with mucosal biopsy is sufficient since the rectum is involved in most cases. Sigmoidoscopy is best performed in the unprepared bowel and with minimal air insufflation especially if the disease is very active. However, in many specialised referral centres in the world, colonoscopy has become the initial choice of investigation because it not only establishes the diagnosis but also determines the extent of the disease. When done by experts, colonoscopy in patients with active ulcerative colitis is a very safe procedure. Colonoscopy should be done only after a severe disease is controlled, preparation should be mild and air insufflation during the procedure should be kept at a minimum. A paediatric colonoscope or a variable stiffness colonoscope may make the procedure quick and safe.

For diagnosing Crohn’s disease, colonoscopy with ileoscopy is mandatory since the rectum is spared in most patients. For diagnosis of Crohn’s disease with only small intestinal involvement, wireless capsule endoscopy and enteroscopy with biopsy is useful (discussed in another chapter).

Severity Grading
Findings on lower GI endoscopy help in grading the severity of the disease (Table 2). The earliest sign of ulcerative colitis is blurring or loss of the mucosal vascular pattern. This is often associated with hyperaemia and oedema of the mucosa. The normally sharp, crescentic valves of Houston get thickened and blunted by oedema. With more severe inflammation, the mucosa becomes granular. Friability is detected by the occurrence of small bleeding points when the mucosa is rubbed. Finally, severe ulcerative colitis is associated with a spontaneously bleeding mucosa with multiple ulcerations. There is no intervening normal mucosa. Following remission the mucosa can return to normal, but in patients who have repeated attacks, it may become thin, pale and atrophic. Interpretation of sigmoidoscopic appearances is subject to considerable interobserver variation, especially with regard to the milder changes of hyperaemia, oedema and granularity. Thus a rectal biopsy specimen always strengthens an assessment of disease severity.

Disease Extent
Colonoscopy is more sensitive than a double contrast enema in diagnosis of the extent of active disease. In one study, 14% of patients with pancolitis had a normal barium enema.

A patient may have proctitis where disease is limited to the rectum only, left-sided colitis where disease extends upto the splenic flexure or pancolitis where the disease extends to mucosa beyond the mid-transverse colon. In all patients with inflammatory bowel disease, the terminal ileum must be intubated whilst performing a colonoscopy to detect “back-wash” ileitis. Most patients with ulcerative colitis will have involvement of the rectum.

Crohn’s disease has a predilection for the distal small bowel and proximal large bowel. Nearly half of all patients will have disease affecting both the ileum and colon. One third of patients will have disease only in the ileum, primarily the terminal ileum. Rarely Crohn’s disease may affect the oesophagus, stomach and duodenum. Exclusive colonic disease is present in 20% to 25% of patients. Anatomic variation may vary over time.

Classical Appearances
Certain characteristic endoscopic features may help differentiate ulcerative colitis from Crohn’s disease (Table 3). Classically, ulcerative colitis will involve the rectum, the mucosa will be uniformly involved without skip areas and in active disease there will be marked mucosal friability. Active disease will be characterised by multiple superficial ulcers in an inflamed mucosa. In severe disease there will be deep ragged ulcers. Granularity and pseudopolyps are more common and cobble-stone mucosa and strictures are less common in ulcerative colitis compared to Crohn’s disease.

In contrast to ulcerative colitis, Crohn’s disease is characterised by rectal sparing and peri-anal disease. Disease is not continuous with multiple skip areas and asymmetrical lesions. The ulcers are usually aphthoid, linear or serpiginous. Compared to ulcerative colitis, cobblestoning and strictures are common whereas friability and granularity are uncommon.

Complications
Endoscopic evaluation is invaluable for detecting and in certain situations treating many local complications of inflammatory bowel disease.

Pseudopolyps
These are common in patients with long standing disease. They can occur in any part of the colon although the rectum is usually spared. Pseudopolyps can vary in size and shape; they may be sessile or pedunculated. However they are usually less than 1.5 cm long. At times they may form mucosal bridges. Pseudopolyps are not premalignant and may occasionally regress.

Stricture
In ulcerative colitis, which is long standing, the colon becomes shortened and narrow at places. However fibrous strictures are uncommon. Importantly, multiple biopsies should be done to exclude carcinoma within these strictures. Many strictures may be asymptomatic. In symptomatic strictures, which are benign, endoscopic balloon dilatation is an alternative to surgery.

Cancer
In patients with extensive disease (pancolitis) which is long-standing (> 10 years) the risk of colorectal cancer is high. The cancers tend to be distributed evenly in the colon. In fact multiple cancers can be present. Colonoscopic surveillance is recommended for patients with long standing extensive disease to look for dysplasia. Multiple biopsy specimens should be taken at 10 cm intervals around the colon with additional biopsy specimens from suspicious areas (so-called dysplasia - associated lesion or mass, DALM). If dysplasia is not found, colonoscopy is repeated at 1 to 3 years. Local facilities and resources usually determine the precise frequency. However, annual surveillance is probably the ideal.

Peri-anal complications
Patients with Crohn’s disease (rarely with ulcerative colitis), develop peri-anal complications. Lesions may be categorised as skin lesions (maceration, superficial ulcers, and abscesses), anal canal lesions (fissures, haemorrhoids) and fistulas (perianal fistulas, rectovaginal fistulas, colovesicular fistulas). Deeper abscesses may arise secondary to fistulas.

Conclusion
Colonoscopy and ileoscopy has become the mainstay of diagnosis and management of patients with inflammatory bowel disease. Certain characteristic features help differentiate ulcerative colitis from Crohn’s disease. However, endoscopic features have to be correlated with the clinical features and histology to make an accurate diagnosis. Endoscopy is useful for detecting complications of inflammatory bowel disease and for surveillance of dysplasia.

Chief Interventional Gastroenterologist, Digestive Diseases and Endoscopy Centre, Motiben Dalvi Hospital, Mumbai. Hon. Gastroenterologist, Jaslok Hospital and Research Centre and Bhatia Hospital, Mumbai.