Mechanical Disorders

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Melanosis coli: characterised by pigmented macrophages in the lamina propria that impart a dusky mucosal appearance mimicking ischaemia. The pigment is lipofuscin and degenerative in nature, and is thought to relate to cellular apoptosis. There is an association with use of laxatives and bowel dysmotility.

Volvulus: usually comprises a markedly dilated atonic sigmoid colon in either Africans (due to a high-fibre diet with bulky stools), or constipation-related acquired megacolon in the elderly. The sigmoid loop twists on its mesentery, obstructs and may become secondarily ischaemic. Resection specimens are often dilated, thinned and featureless. Melanosis coli may be present. Congenital megacolon and Hirschsprung's disease are discussed elsewhere (see page 232).

Pneumatosis coli: submucosal gas cysts lined by macrophages and giant cells with overlying mucosal chronic inflammation or pseudolipomatosis. There is an association with volvulus, constipation, diverticulosis and chronic obstructive airways disease. Pathogenesis relates to retroperitoneal tracking of air into the bowel mesentery, abnormal luminal gas production linked to the increased intraluminal pressure seen in the above disorders, and introduction of gas during endoscopy. About 50% of cases resolve but recurrent or severe lesions may require colectomy of the involved segment.

Obstructive enterocolitis: continuous or segmental areas of inflammation or ulceration adjacent to or distant from an obstructing distal lesion, e.g., annular carcinoma or diverticulosis. Small bowel may also be involved with mimicry of Crohn's disease. A dilated, thinned caecal pouch can become ischaemic and perforate.

Diverticulosis: very common in Western society due to a low-fibre diet, high intraluminal pressure and subsequent transmural mucosal herniation in the sigmoid colon through points of vessel entry from the mesentery. Presentation is with altered bowel habit, per rectum bleeding, left iliac fossa pain or a mass. The latter implies diverticulitis with possible perforation and peri-colonic reaction/abscess formation. Portal pyaemia, liver abscesses and peritonitis can ensue. The diverticular segment is thickened and contracted with muscle coat hypertrophy and visible diver-ticular pouches in the muscularis and mesenteric fat. They may be filled and obstructed with faecal or vegetable debris, and ulcerated with a coating of pericolonic exudate and abscess. The concertina-like redundant mucosal folds can show crescentic colitis due to abrasion of their tips by the passing faecal stream. Occasionally, the chronic inflammation may be transmural and granulomatous mimicking or co-existing with Crohn's disease. Treatment is often conservative, e.g., by diet alteration, but severe or complicated cases require colectomy. Co-presentation with an occult carcinoma within the strictured segment must be excluded by careful pathological examination.

Mucosal prolapse: a mechanism producing reactive mucosal changes of crypt hyperplasia, smooth-muscle thickening of the lamina propria and variable surface erosion. It is common to a number of situations including: solitary rectal ulcer syndrome (SRUS), inflammatory cloacogenic polyp, diverticular-related crescentic colitis, mucosa adjacent to a polyp, stricture or tumour, stercoral trauma and the mucocutaneous junction of stomas. In SRUS there is a history of abnormal anterior rectal wall descent due to straining at defaecation. This results in induration of the wall that can mimic a plaque of tumour on palpation and rectoscopy. Biopsy is diagnostic and treatment is usually conservative, related to better stool habit - occasional cases require resection of the involved sleeve of mucous membrane with apposition and plication of the intervening muscle (Delorme's procedure).

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Constipation Prescription

Constipation Prescription

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