The patient is reassured and warned that some discomfort might be felt, which can be alleviated to some extent by deep breathing. There may also be the desire to defaecate. Normally no bowel preparation is necessary and the procedure can be undertaken readily on out-patients. Enemas and suppositories have the disadvantage that they alter the natural state of the mucous membrane, washing away secretions and causing hyperaemia, which is an important consideration when the diagnosis of ulcerative colitis is being considered: enemas not only add to the difficulties of making a diagnosis but are potentially dangerous. It is reasonable to give a saline enema if a cancer of the colon is being considered and a large amount of faecal material is present. Various disposal enemas are available for out-patient use, but they may all cause mucosal irritation.

The patient may be examined on a surgical table; or an examination couch; or in the hospital bed, in which instance it is helpful to place a fracture board under the mattress to ensure that the patient lies in the correct position. Two positions are recommended: the left lateral and knee-chest. The left lateral is preferred because it is more comfortable for the patient. For the proctosigmoidoscope to be successfully introduced, it is essential that the patient is correctly positioned: well flexed and lying transversely across the bed with the buttocks positioned at the very edge. The knees are slightly extended. A sandbag or pillow can be placed under the left hip, which is positioned at the edge of the couch. The left shoulder is tucked under the body and the right arm is brought forward. The head rests on a flat pillow. Failure to pass the proctosigmoidoscope fully is frequently the consequence of faulty positioning, particularly when the procedure is performed at the bedside. A soft mattress causes marked twisting of the spine, making it difficult to negotiate the curves in the rectum and lower colon. The position of the examiner is also important; he must be comfortable and relaxed and this is best achieved by either sitting on a low stool or kneeling at the bedside.

The knee-chest position may sometimes be helpful if there is much loose stool and blood, but is much less comfortable for the patient and is not recommended. In this position the knees are well drawn up and the back arched so that there is a distinct lumbar lordosis; the face is turned to one side, the chest and shoulders rest on the couch and the arms drop over the side of the couch. Multi-purpose tables are available which enable the patient to be tilted into the knee-chest position.

Before introducing the instrument the light connections are checked and the proctosigmoidoscope is warmed. It is lubricated and an anaesthetic jelly is used if necessary. A digital examination of the rectum is made and the patient warned that the instrument is about to be introduced.

The obturator is inserted in the proctosigmoidoscope and the instrument held in the right hand. It is introduced into the anus using a rotary movement and the tip is directed forwards for 5 cm in the direction of the umbilicus. The obturator is removed and the eye piece attached. From this point the examination is performed under direct vision with gentle air insufflation. The instrument is now advanced in a backward direction and enters the rectum by following the curve of the sacrum.

As the instrument is advanced it may become necessary to separate the mucosal folds by inflating with air, but this is kept to a minimum as it is both uncomfortable for the patient and potentially dangerous. Small pieces of stool usually can be moved out of the way with the end of the instrument; they are sometimes of value in indicating the position of the bowel lumen. Stool which occludes the end of the proctosigmidoscope may be removed by introducing the obturator, withdrawing the instrument slightly and then removing the obturator. Another way is to displace the stool with a swab which is attached to a swabholding forceps. Occasionally the forward passage of the instrument is prevented by spasm of the bowel, but if the proctosigmoidoscope is withdrawn slightly and held still for a short while the spasm will disappear and it is possible to proceed with the examination.

The rectal mucosa is smooth and it is easy to see the rectal valves. The rectosigmoid junction is reached 12–15 cm from the anal margin. This is at the level of the sacral promontory and is identified by the change of the mucosa to concentric rugal folds. The rectosigmoid junction is usually sharply angled and may be difficult to traverse: the proctosigmoidoscope is directed anteriorly and to the right but the sharp angling may cause some discomfort. In many examinations it is impossible to lever the proctosigmoidoscope through the rectosigmoid junction without undue discomfort. The sigmoid colon is not reliably reached. The average penetration is 20 cm in men and 18.5 cm in women, but it is uncertain how far along the sigmoid colon the instrument passes, and it is probable that a mobile colon is simply displaced forwards. However, about 5 cm of the sigmoid may be seen. The instrument is now slowly withdrawn, the mucosa carefully rescrutinized and biopsies taken as required. After withdrawal of the instrument the patient is cleaned and any stool adhering to the sigmoidoscope is taken for examination. A full description of the procedure should include the distance to which the proctosigmoidoscope was introduced, the appearance of the mucosa, the presence of blood or mucus and the appearance of the stool, and whether a biopsy was taken and the site.

The mucous membrane is pink, it is not friable and should not bleed with the gentle passage of the instrument. Undue bleeding during the examination suggests that the mucosa is abnormal. The normal vascular pattern is well visualized and comprises a network of small arterioles and to a lesser extent of venules. The rectal valves are sharp and crescentic in shape. A small amount of mucus may be seen.

The appearances vary according to the stage of the disease. In the acute stage the mucosa is reddened, friable and haemorrhagic,and no vascular pattern can be seen. Thickening of the rectal valves almost to the point of obliteration indicates the presence of mucosal oedema. Ulcers are rarely distinguished and when seen appear shallow and irregular. There is nothing specific about these appearances, which are also seen in acute bacillary dysentery, occasionally in amoebic dysentery and in various toxic states. In the subacute and chronic stages of ulcerative colitis the normal vascular pattern is obscured, the mucosa is reddened and granular and bleeds readily when gently stroked by the sigmoidoscope or a swab. It is probable that some degree of mucosal abnormality such as excessive friability remains even with the most chronic and inactive colonic involvement. Proctosigmoidoscopy is of value in distinguishing ulcerative colitis from ulcerative proctitis, in which only the terminal 10–12 cm of bowel is diseased.

The appearance is very similar in bacillary dysentery to that seen in acute ulcerative colitis. The mucosa in amoebic dysentery contains small flask-shaped ulcers containing a small bead of pus, but is otherwise normal. However, the picture is variable and the mucous membrane may be quite reddened and inflamed, and may at times present a picture not unlike that of acute ulcerative colitis.

About half of all large bowel cancers may be seen with the rigid proctosigmoidoscope, and three-quarters are visible with the flexible sigmoidoscope. Malignant growths are seen as infiltrating or ulcerating lesions with a varying amout of haemorrhage and necrosis. Other new growths include lobulated pink or red adenomatous polyps and sessile, branching soft villous adenomas. A neoplasm should be suspected if altered or fresh blood is seen in the lumen of the bowel ahead of the proctosigmoidoscope. Screening populations at the age of 50–55 years using flexible sigmoidoscopy has been proposed as an effective way of detecting early cancer.

Pneumatosis cystoides intestinalis shows as multiple glistening blue-purple submucous cysts. Crohn’s disease of the colon is difficult to distinguish from the other forms of colitis, but a nodular ‘cobblestone’ appearance of the mucosa with discrete ulcers suggests this disease. The rectum is less frequently involved in granulomatous than in ulcerative colitis. In diverticular disease the mucosa may be reddened or normal, and the orifices of the diverticula will be seen with the flexible instrument. A false impression of the colonic mucosa is obtained when suppositories or enemas are given prior to examination. The mucosa may become reddened and oedematous and appear very abnormal. Difficulties are also found in patients with severe diarrhoea from any cause because marked mucosal hyperaemia may be present in the absence of specific colonic disease.

The glands are seen to be tubular and closely packed and the epithelium is columnar. There are numerous goblet cells. The lamina propria contains a moderate number of lymphocytes, plasma cells, reticuloendothelial cells and the occasional eosinophil. Variations within the normal range include slight dilatation or tortuosity of the glands, cuboidal surface epithelial cells and some increase in round cells in the lamina propria. The rectal glands are bulbous and shortened in specimens obtained from near the anal region. Homosexual men often have nonspecific cellular infiltration in the lamina propria, without pathological significance.

In severe cases there is marked loss of glandular structure, extensive mucosal ulceration with a heavy infiltration of cells particularly polymorphonuclear leukocytes, crypt abscesses, and a reduction in goblet cells and mucus. In moderate and mild inflammation there is oedema, dilatation of vessels, an occasional crypt abscess and superficial ulceration. There is an increase in lymphocytes, plasma cells and polymorphonuclear leukocytes. There is generally good correlation between the sigmoidoscopic and histological findings but this is not always so. The biopsy specimen is more likely to show inflammation when the proctosigmoidoscopic findings are normal than the reverse. Once the disease has developed, the mucosa remains permanently abnormal in the majority of patients whether or not symptoms are present. Biopsy samples obtained during a quiescent phase show a reduction in the number of rectal glands which tend to be bulbous, tortuous and branched. There is nothing specific about the mucosal biopsy in ulcerative colitis and all the features of the mucosal alterations in this disease may be found in colitis from other causes.

Rectal biopsies are valuable in the diagnosis of precancer dysplasia in patients with ulcerative colitis. There are two main types of abnormality: the polypoid variety, and precancerous change in a flat mucosa. Polypoid precancerous changes are recognized by the presence of multiple polyps which are usually sessile with a villous or papillary surface configuration. The villous growth pattern is the more significant. There is obvious inflammation in the lamina propria with loss of goblet cells. The nuclei are hyperchromatic with many mitotic figures.

Precancerous change in a flat mucosa is more common. The mucosa is thicker and has a fairly nodular surface. The epithelial tubes are irregular in shape and size with lateral budding and a villous growth pattern. There is a tendency for the epithelial tubes to proliferate into the submucosa. A moderate amount of inflammatory cell infiltration is present. The implication of these histological features in the management of chronic ulcerative colitis remains uncertain, but it is generally taken to indicate a need for close surveillance and possibly elective colectomy if severe or progressive.

The mucosa is usually normal or shows non-specific inflammatory changes. It is helpful but unusual to find non-caseating giant-cell systems in the biopsy specimen.

A papillary or villous adenoma will show a broad base with characteristic long papillary projections springing almost directly from the basement membrane. An adenomatous polyp shows focal glandular hyperplasia; there may be short papillary projections but there are always numerous glands below the surface epithelium and the villi do not extend to the submucosal base. The stalk is often fibromuscular in character. Colonic cancers are usually adenocarcinomas and less frequently colloid cancers.

It is claimed that 50% or more of patients with light infections with S. mansoni will be diagnosed if rectal biopsies are taken than if only the stools are examined. Rectal biopsies are useful also in S. haematobium infections. The ova are easily recognized when a fresh unstained biopsy of mucosa is compressed between two glass slides and examined under the microscope.

Rectal biopsies have been used to advantage in the diagnosis of amoebic colitis, amyloidosis, histiocytosis, some of the neurolipidoses and metachromatic leukodystrophy. Hirschsprung’s disease can be detected with the use of special stains for nerve fibres and acetycholinesterase activity, but requires deeper biopsies than usually can be safely obtained sigmoidoscopically.