Diverticulosis, colon

Clinical features

In the large majority of patients diverticulosis will not produce any symptoms. Some of them may complain of intermittent mild abdominal pain relieved by the passage of stools, flatulence, bloating and alternating bouts of constipation and diarrhoea. These symptoms are very similar to those of irritable bowel syndrome and because both conditions are so common may in fact be related to co-existent conditions.

General features

Diverticulosis is now the most common disease of the colon in individuals from the Western world. It rarely affects young persons below the age of 40 years but its incidence reaches 33 - 50% in patients older than 50 years and more than 60% in patients above 80 years. On the contrary, the disease occurs very rarely (0.2%) in the countries of the developing world, but if individuals from these countries adopt western lifestyle the prevalence of diverticulosis will increase in this population too.

Based on the observation of the inverse relationship between the amount of roughage in the food and the incidence of diverticulosis, it was suggested that the development of the disease in the Western world during the last century is due to the fundamental change in the diet, i.e. the change from coarse, unrefined bread to that made from roller milling flour which is low in fibres. Diverticulosis in the Western world is observed with equal frequency in both sexes. Clinically diagnosed diverticulosis will lead to complications like diverticulitis and haemorrhage in more than 20% of cases.

Although the pathogenesis of diverticular disease of the colon is not yet fully understood, it is generally accepted that the two main responsible factors are the increased pressure in the lumen of the colon and the areas of weakness in the wall of the colon. The sigmoid has the smallest diameter of any segment of the colon and therefore the highest intraluminal pressure. Excessive segmentation, a form of nonpropulsive colonic contraction, due to segmental narrowing in the sigmoid colon, may lead to high segmental pressure and causing the extrusion of diverticula at the weakest points i.e. where the intramural vasa recta penetrate the submucosa. Increased segmentation may be related to low fibre, low residue diet as small dehydrated stools may stimulate excessive motor activity and segmentation of the sigmoid colon. In elderly people the collagen fibres become atrophic and the elastine fibres deteriorate with the exception of those in the tenia which become contracted. Deterioration of structural proteins in the colon wall may explain why diverticula of the colon are seen at a young age in patients with collagen diseases such as Ehlers Danlos syndrome and Marfan syndrome.

Pathology

The diverticula seen in diverticulosis of the colon are acquired herniations and usually only contain mucosa and submucosa although some authors report the presence of muscularis mucosa. An increased number of lymphoid follicles is found in the diverticula which is explained as an inflammatory reaction to prolonged faecal stasis. Indeed the diverticula are covered by a thin layer of longitudinal muscle only and although compressible empty rather poorly. Diverticula of the colon are mostly small with a diameter varying between 5 and 10 mm and their orificium may even be smaller. They penetrate the clefts between the circular muscle fibres at those points where nutritient arteries pass through the submucosa.

The close proximity of diverticula and arteries explains why bleeding is a frequent complication of diverticulosis. It has been shown that diverticula of the colon arise in four rows: one on each side of the mesenteric tenia and one on the mesenteric side of the omental teni diverticulosis, probably because at the level of the rectum the whole surface of the colon is covered by the fused tenia that provide a protective coat. In Asian countries there is a clear dominance of right-sided diverticula as compared to the left side. Another unexplained observation is that rightside diverticula tend to arise at a younger age than the leftsided ones.

Radiographic features

Diverticula may be visible on plain abdominal film because they entrap gas pockets "the bubbly gas" appearance or because of retained barium from previous barium studies. There is also a striking association between the presence and number of pelvic phleboliths and diverticulosis of the colon, suggesting that the some similar aetiological factors may play a role in both conditions. Rightsided colonic diverticulas, more frequently seen in the East, may contain calcifications and thereby simulate gallstones.

On barium contrast enema (Fig.2) (Fig.3) diverticula will appear as globular small protrusions from the lumen of the colon, variable in size, with a short neck. They may fill completely with contrast medium but sometimes only the peripheral area of the diverticulum is outlined by contrast medium because of the presence of faecal contents. Double contrast barium study will better visualize small intramural diverticula and will in general display diverticula better because of more pronounced colon distension. Depending on the angle from which they are visualized and from the amount of barium that they contain, colon diverticula present a variable appearance on double contrast barium enema. Larger diverticula appear as barium- or airfilled protruding structures when projected in profile. En face they may appear as a ring shadow, as a well marginated barium collection, or may resemble a bowler hat.

Diverticula seen en face may simulate the aspect of small polyps. Films taken from different angles and in different positions of the patient will demonstrate the filling of the diverticulum with contrast medium, the presence of an air-fluid level or the protruding character outside the colon contour. The ring shadow caused by the barium lining of an air-filled diverticulum that is visualized en face will typically exhibit a smooth outer margin and a hazy inner margin (meniscus sign fading inward) whereas the reverse signs will be noted for a polyp covered by barium (meniscus sign fading outward). Another difficulty in the differential diagnosis between small polyps and diverticula is occasionally caused by a diverticulum, that is completely filled by faecal contents, and by projecting in the lumen will cause a filling defect. A small filling defect may also be produced by obstruction of the orifice of a diverticulum by faeces causing the diverticular orifice to bulge into the lumen. Both polyps and diverticula can produce the "bowler hat" sign. However, if the bowler hat points away from the long axis of the lumen of the colon it would represent a diverticulum rather than a polyp. Inverted diverticula of the caecum may produce a caecal filling defect, simulating a polyp.

CT features of diverticulosis are multiple air or contrast medium containing small round structures lying outside but along the colon lumen, as well as mural thickening of the colon wall to more than 4 or 5 mm in width.

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