In IBD, the gross appearance of the colon depends on the stage of the disease and the clinical severity . In UC, the mucosa of the distal colon in early phases is red, friable, mucoid, with petechial haemorrhages.
With the progression of the disease, broad-based ulceration of the mucosa develops, separating isolated islands of mucosa which could be inflamed or show features of regeneration. They may be seen to be protruding into the lumen to create the so-called pseudo-polyps commonly seen in this disease. We discourage the use of the term pseudo-polyp as a polyp is a mucosal protrusion and the surviving islands often undergo regenerative or inflammatory changes, and thus can be regarded as polyps. We therefore designate these polyps as either inflammatory, regenerative polyps or polypoid mucosal tags. These polyps are typically small and multiple; however, sometimes they can attain a large size mimicking carcinoma . These polyps do not correlate with the disease severity and are not precancerous. Commonly, the ulcers are aligned along the long axis of the colon. In chronic cases or in cases where the disease has healed, the mucosa shows atrophy with flattening of the surface and becomes featureless. The serosa usually shows no abnormal features except in cases of toxic megacolon where the bowel wall is massively dilated and the wall is very thin and liable to perforate . In this case, distinguishing UC from CD becomes difficult macroscopically or even, indeed, microscopically. In one study, the surgeons and pathologists failed to accurately differentiate UC from CD intra-operatively and on examining the gross appearance in the 198 patients entered in the study, they concluded that the distinction between the two conditions should not be made macroscopi-cally . In the same study, cobblestone mucosa was most common in Crohn's disease and inflammatory polyps were commonly seen in ulcerative colitis; however, there was considerable overlap, and a similar incidence of strictures and skip lesions occurring in both diseases.
In CD, every organ in the gastrointestinal tract can be involved from the mouth to the anus; however small intestinal involvement can occur between 25-50% of cases. The most distinguishing feature of CD is that it is a discontinuous disease and grossly demonstrated by a sharp demarcation between unin-volved and diseased segments commonly called 'skip lesions' . The diseased bowel shows thickened, fibrotic, dull brown, granular and hyperaemic seros-al surface that is sometimes covered by exudate. Fibrous adhesions between the small bowel loops are often present. The mesenteric fat usually wraps around the bowel (creeping fat), which has been shown to correlate with transmural inflammation . The wall of the intestine is commonly thick and rubbery, which often leads to a narrow lumen that shows the characteristic radiological "string sign". The mucosa shows focal ulceration with oedema and loss of a normal appearance. Serpentine linear and
discontinuous ulcers develop along the long axis of the bowel with the intervening unremarkable mucosa sometimes connected by short transverse ulcers leading to the cobblestone appearance . Fissures commonly develop which penetrate deeply to cause serositis. Thus sinuses and fistulas are common features of this disease . Villiform inflammatory/hyperplastic polyps are sometimes seen in CD .
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