Diverticula of colon.

DIvERTicuLA occur in the large bowel and are herniations of the mucous membrane through acquired defects in -the muscular coats-the small pouches being covered by serosa; exicept in the smallest sacs muscle fibres are only found in the neck. When first 'formed the necks are wide and the diverticula globular-later the necks become attenuated and the pouches flask shaped. The appendices epiploicae when heavily fat laden tend to obscure the diverticula. The diverticula iarise between the mesenteric and antimesenteric taeniae near the site of entry of the small perforating vessels, consequently diverticula are not found in the rectum where the longitudinal muscle is complete. The commonest site is the pelvic colon and in many cases is the only part involved. Diverticula in the caecum and ascending colon are rare, tend to be solitary and when inflamed simulate appendicitis. Under 40 years diverticula are uncommon but after the 4th decade 5-10% of adults have diverticulosis. mostly asymptomatic. Painter (1964) has investigated intracolonic pressure in volunteer subjects by means of three open-ended water-filled polythene tubes with metal tips, inserted through a sigmoidoscopethe tips being 3 inches apart from each other. He did not find any intraluminal hypertension in diverticulosis under resting conditions but after injection of morphine, tracings recorded from the immediate vicinity of diverticula showed very high pressures compared with those from normal bowel after morphine. Continuing his investigations with cine-radiography Painter outlined the colon with thin barium injected through one of the polythene tubes; he demonstrated that diverticula are reducible and vary in size according to local pressure in the bowel. Following an injection of morphine the bowel, bearing diverticula, narrowed, the diverticular necks contracted whilst the diverticula enlarged as barium was forced into therm. Colonic movements were generally increased. Jf probanthine was 'then given, this caused paralysis of the bowel muscle, the colon dilated, !the diverticular necks reopened, barium drained back into the relaxed bowel and the intrasigmoid pressure fell. Painter found after morphine the colon in diverticulosis localised pressure by altering the configuration of its wall, as it was seen to 'be segmented in the vicinity of any tip which was recording changes of pressure. The segments were defined by interhaustral contraction rings which narrowed and at times completely occluded the colonic lumen, so the colon functioned as a series of bladders and not as a tube. Very high pressures resulted if one segment, isolated from its fellows, contracted forcibly as its contents could not escape. As segments of colon bearing diverticula produce pressures after morphine differing from those recorded from their neighbours, and from segments of healthy colon, it is possilble that the diseased segments also react excessively to natural stimuli such as eating, drinking and emotion which are known to activate the colon. Painter is uncertain whether this ability of affected segments to behave differently precedes the appearance of diverticulosis and is iesponsible for its causation or whether it is result of the disease. Most probably the differential response is present in the early stages of the disease process and is responsiible for the progressive nature of diverticulosis. The ripple-edge border of the sigmoid colon seen on barium enema examination 'has been regarded as a prediverticular state but Marcus and Watt (1964) consider it indicates established diverticula at an early stage. Bilateral irregularities of contour indicate small but definite diverticula in the lateral .intertaenia areas. When the sawtooth outline is unilateral it is due to diverticula in the antimesenteric intertaenia area.