Benign tumours

The rectum, along with the sigmoid colon, is the most frequent site of polyps (and cancers) in the gastrointestinal tract. All neoplastic polyps of the colon and rectum (with rare exceptions) have a tendency to become malignant. This tendency is greatly enhanced if the polyp is more than 1 cm in diameter, shows obvious signs of increasing size and has a sessile rather than a penduculated shape. For these reasons, removal of all polyps is recommended, and total removal is mandatory. Only total removal will give complete histological examination and exclude (or confirm) localised carcinoma in situ, and also prevent local recurrence. For these reasons, destruction of anorectal tumours by fulguration is not the best treatment, and should be used for only the tiniest polyps. If one or more rectal polyps are discovered on sigmoidoscopic examination, a colonoscopy must be performed as further polyps are frequently found in the colon and treatment may be influenced. No rectal tumour should be removed until the possibility of a proximal carcinoma has been ruled out, otherwise local implantation of cancer cells may occur in the distally situated rectal wound.

The rectum shares substantially the same spectrum of polyps as the colon. Polyps are described chiefly in terms of their tissue organisation. For further clinical details the reader is referred to Chapter 67. Certain polyps which have features relevant to the rectum are now described.

Polyps relevant to the rectum

Juvenile polyp

This is a bright red glistening pedunculated sphere (‘cherry tumour’) which is found in infants and children. Occasionally it persists into adult life. It can cause bleeding, or pain if it prolapses during defecation. It often separates itself, but can be removed easily with forceps or a snare. It has virtually no tendency to malignant change but should be treated if it is causing symptoms. It has a unique histological structure of large mucus-filled spaces covered by a smooth surface of thin rectal cuboidal epithelium (Fig. 60.18).

Meta plastic polyps

These are small, pinkish, sessile polyps 2—4 mm in diameter and frequently multiple. They are harmless.

Pseudo polyps

These are oedematous bosses of mucous membrane. They are usually associated with colitis in the UK, but most inflammatory diseases (including tropical diseases) can cause them. They are more likely to cause radiological difficulty as the Sigmoidoscopic appearances are usually associated with obvious signs of the inflammatory cause.

Villous adenomas

These have a characteristic frond-like appearance. They are often of very large size, and occasionally fill the entire rectum. The large tumours have an enhanced tendency to become malignant — a change that can be detected most easily by palpation with the finger; any hard area should be assumed to be malignant and should be biopsied.

Rarely, the profuse mucous discharge from these tumours, which is high in potassium content, causes dangerous electrolyte and fluid losses (Fig. 60.19).

Provided cancerous change has been excluded, these tumours can be removed either by submucous dissection per anum, or by sleeve resection from above. Only very unusually is rectal excision required, and then only when malignant change has occurred. A recent technique known as transanal endoscopic microsurgery (TEM) has been developed (Buess) which has improved the endoanal approach for the local removal of villous adenomas. The method requires the insertion of a very large operating sigmoidoscope. The rectum is distended by carbon dioxide insufflation, the operative field is magnified by a camera inserted via the sigmoidoscope, and the image is displayed on a monitor (Fig. 60.20). The lesion is excised using specially designed instruments with the surgeon observing the monitor screen. The technique is highly specialised and takes a considerable amount of time to master.

All neoplastic polyps can be solitary or multiple. Small colonic polyps (under 5 cm in size) can now be snared through the colonoscope. This instrument has revolutionised the treatment of multiple polyps.

Familial adenomatous polyposis

(formerly known as familial polyposis co/i)

This disease usually manifests itself by the development of multiple rectal and colonic polyps around puberty. A colonoscopy and biopsy will confirm the presence of multiple colonic adenomatous polyps. Recently the adenomatous polyposis cell (APC) gene responsible for the disease has been isolated on chromosome 5 (Bodmer). This discovery should make screening of affected families far more cost effective than at present. As this condition is premalignant, a total colectomy must be performed, but often the rectum can be preserved by regular fulguration of polyps before they develop carcinoma. The operation of restorative proctocolectomy with pouchanal anastomosis is now being used in most centres of coloproctology: the rectum is replaced by a ‘pouch’ of folded ileum (Chapter 57). A pan-proctocolectomy with permanent ileostomy is necessary in some instances, especially when patient follow-up may he impractical.

Differential diagnosis

Bilharzia

In patients who have lived in Egypt, or any country where bilharzial infestation is rife, bilharzial papilloma must be excluded.

Treatment. Diathermy coagulation is satisfactory in the case of a small papilloma, but the patient must be examined at regular intervals as recurrence is common, as in the case of the bladder. For large papillomas, especially the sessile variety, excision of the rectum may be the only curative treatment. Some cases (not, as a rule, those invading the anal canal) are suitable for conservative resection of the rectum. In a few cases intestinal continuity can be restored by a low coloanal ‘sleeve’ anastomosis or one achieved by the circular stapling gun.

Benign lymphoma. This occurs as a circumscribed movable nodule, firm but not hard, greyish-white to pink in colour, and is essentially submucosal. This neoplasm, which occurs at all ages and in both sexes, has no definite capsule. Notwithstanding, complete local excision us curative.

Endometrioma. Endometrioma is rare, and as a rule is diagnosed as a carcinoma. This neoplasm produces either a constricting lesion of the rectosigmoid or a tumour invading the rectum from the rectovaginal septum. The latter variety gives rise to a very tender submucous elevation of the rectal wall. Endometrioma occurs usually between 20 and 40 years of age; less often at the menopause. Dysmenorrhoea with rectal bleeding are the main symptoms. On sigmoidoscopy endometriosis involving the rectosigmoid junction usually presents as a stricture with the mucous membrane intact. Bilateral Oophorectomy may he followed by regression of the tumour, tendering resection unnecessary. The contraceptive pill is also effective as it inhibits ovulation

Haemangioma. Haemangioma of the rectum, which is an uncommon tumour, is a cause of serious and, if the neoplasm is large, sometimes fatal haemorrhage. When localised in the lower part of the rectum or anal canal, a haemangioma can be excised after applying. Goodsall’s ligature. When the neoplasm is diffuse, or lying in the upper part of the rectum, the symptoms simulate ulcerative colitis, and often the diagnosis is missed for a long period. At other times, the neoplasm is mistaken for a vascular carcinoma, an error which, fortunately, is not often a cause for serious regret because the correct treatment of an extensive haemangioma is excision of that portion of the anorectum hearing the neoplasm. Lesser procedures are followed nearly always by recurrence amid renewed loss of blood.

Leiomyoma. Benign smooth muscle tumours of the rectum are tare. They consist of spindle cells. It is often difficult to predict how they will behave. If the mitotic rate is high, and if there is variation in number, size and shape, hyperchromasia and frequent bizarre cells, these tumours are likely to metastasise. In these circumstances, they should he classified as leiomnyosarcomas. This uncertainty in their behaviour means that treatment should, whenever possible, he by radical excision.