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.