Carcinomas
Colorectal carcinoma is the fourth most common
variety of malignant tumour found in women, and its frequency in men is
surpassed only by carcinoma of the bronchus and stomach. Overall, it is the
second most common carcinoma in the Western countries, with approximately 18 000
patients in the UK dying per annum. The rectum is the most frequent site
involved.
Origin
In many cases, operation specimens show that
in some part of the bowel that has been removed, in addition to the carcinoma,
there are one or more synchronous adenomas or papillomas, proof indeed that
adenoma and papilloma of the rectum are precarcinomatous conditions. In
approximately 5 per cent of cases,
there is more than one carcinoma present. It is now believed that most rectal
cancers start as an adenoma and this is due to a series of genetic changes
which progressively change the adenoma from one that is not dysplastic to one
that shows severe dysplasia and finally becomes a carcinoma (the
adenoma—carcinoma sequence) (Vogelstein) (Chapter 67).
Pathological
histology
Three types are recognised:
•
well-differentiated adenocarcinoma;
•
averagely differentiated adenocarcinoma;
•
anaplastic, highly undifferentiated adenocarcinoma.
Usually
these carcinomas present as an ulcer, but papilliferous and infiltrating types
are common.
Types of
carcinoma spread
Local spread
Local spread occurs circumferentially rather
than in a longitudinal direction. Usually a period of 6 months is required for
involvement of a quarter of the circumference, and 71 8 months to 2 years for
complete encirclement, the annular variety being common at the rectosigmoid
junction. After the muscular coat has been penetrated, the growth spreads into
surrounding mesorectum, but is still limited by the fascia propria (perirectal
fascia). Eventually, the fascia propria is penetrated but this occurrence is
rare before 18 months from the commencement of the disease. If penetration
occurs anteriorly, the prostate, seminal vesicles or the bladder become
involved in the male; in the female the vagina or the uterus is invaded. In
either sex, if the penetration is lateral, a ureter may become implicated, while
posterior penetration involves the sacrum and the sacral plexus. Downward spread
for more than a few centimetres is rare except in anaplastic tumours.
Lymphatic spread
Enlargement of lymph nodes from bacterial
infection is more frequent than enlargement from metastasis, and microscopical
examination is required to detect carcinomatous involvement of the nodes.
Lymphatic
spread from a carcinoma of the rectum above the peritoneal reflection occurs
almost exclusively in an upward direction;
below that level to within 1—2 cm of the anal orifice the lymphatic spread is
still upwards, hut the first halting
place is in the pararectal lymph nodes of Gerota. The exception to this rule is
when the neoplasm lies within the field ~ the middle rectal artery, i.e.
between 4 and 8 cm from the anus, in which case primary lateral spread along the lymphatics that accompany the middle rectal
vein is not infrequent.
Downward spread is exceptional, drainage along the subcutaneous lymphatics to the
groins being confined, for practical purposes, to the lymph nodes draining the
perianal rosette and the epithelium lining the distal 1—2 cm of the anal
canal.
Metastasis
at a higher level than the main trunk of the superior rectal artery occurs only
late in the disease. A radical operation should ensure that the high-lying lymph
nodes are removed by ligating the inferior mesenteric artery and vein at the
highest possible level.
Atypical
and widespread lymphatic permeation can occur in highly undifferentiated
neoplasms.
Venous spread
As a rule, spread via the venous system occurs
late, except in that portion of the anal canal where the anoderm is firmly
adherent to deeper structures. Anaplastic and rapidly growing tumours in
younger patients are much more liable to spread in this way than tumours of
relatively low malignancy. The principal sites for blood-borne metastases are:
liver (34 per cent), lungs (22 per cent) and adrenals (11 per cent).
The remaining 33 per cent is divided among the
many other locations where secondary carcinomatous deposits are wont to lodge,
including the brain.
Peritoneal dissemination
This may follow penetration of the peritoneal
coat by a high-lying rectal carcinoma.
Stages of
progression
As a rule, carcinoma of the rectum does not
metastasise early.
Dukes classified carcinoma of the rectum into
three stages
A
The growth is limited to the rectal wall (15 per cent). Prognosis
excellent.
B
The growth is extended to the extrarectal tissues, but no metastasis to
the regional lymph nodes (35 per cent). Prognosis reasonable.
C
There are secondary deposits in the regional lymph nodes (50 per cent).
These are subdivided into C1 where the local pararectal lymph nodes alone are
involved, and C2 where the nodes accompanying the supplying blood
vessels are implicated up to the point of division. This does not take into
account cases that have metastasised beyond the regional lymph nodes or by way
of the venous system. Prognosis bad.
Low
grade = well-differentiated 11
%
Prognosis good
tumours
Average
grade
64%
Prognosis fair
High grade = anaplastic tumours
25% Prognosis poor
Colloid
carcinoma. This type of carcinoma is present in 12 per cent of cases. There are
two forms: primary and secondary; much the more frequent is secondary mucoid
degeneration of an adenocarcinoma. Histologically the glandular arrangement is
preserved and mucus fills the acini. This type is of average malignancy. In a
small number of cases the tumour is a primary mucoid carcinoma. The mucus lies
within the cells, displacing the nucleus to the periphery, like the seal of a
signet ring. Primary mucoid carcinoma gives rise to a rapidly growing bulky
growth which metastasises very early and the prognosis of which is very bad.
Clinical
features
Carcinoma of the rectum is not uncommon early
in life, and when the disease commences in youth, in spite of radical treatment,
death usually results within a year. However, the adult age of presentation is
above 55 years. Often the early
symptoms are so slight that the patient does not seek advice for 6 months or
more.
Bleeding
Bleeding is the earliest and most common
symptom. There is nothing characteristic about the time at which it occurs,
neither is the colour or the amount of blood distinctive; often the bleeding is
slight in amount, and occurs at the end of defecation, or is noticed because it
has stained underclothing. Indeed, more often than not, the bleeding in every
respect simulates that of internal haemorrhoids (haemorrhoids and carcinoma
sometimes coexist) and it is lamentable that, in spite of oft-repeated
exhortations, the patient’s doctor sometimes fails to examine the rectum but
prescribes a salve while the growth advances to inoperability (see footnote,
Chapter 59).
Sense of incomplete defecation
The patient’s bowels open but there is the
sensation that there are more faeces to be passed (tenesmus, a painful straining to empty the bowels without
resultant evacuation). This is a very important early symptom and is almost
invariably present in tumours of the lower half of the rectum. The patient may
endeavour to empty the rectum several times a day (spurious diarrhoea), often
with the passage of flatus and a little blood-stained mucus (‘bloody
slime’).
Alteration in bowel habit
This is the next most frequent symptom. The
patient may find it necessary to start taking an aperient, or to supplement the
usual dose, and as a result a tendency towards diarrhoea ensues. A patient who
has to get up before the accustomed hour in order to defecate, and one who
passes blood and mucus in addition to faeces (‘early morning bloody diarrhoea’),
is usually found to be suffering from carcinoma of the rectum. Usually, it is
the patient with an annular carcinoma at the pelvirectal junction who suffers
with increasing constipation, and the one with a growth in the ampulla of the
rectum with early morning diarrhoea (Bruce).
Pain
Pain is a late symptom, but pain of a colicky
character accompanies advanced growths of the rectosigmoid, and is due to some
degree of intestinal obstruction. When a deep carcinomatous ulcer of the
rectum erodes the prostate or bladder, there is severe pain. Pain in the back,
or sciatica, occurs when the growth invades the sacral plexus. Weight
loss is suggestive of hepatic metastases.
Early symptoms of rectal cancer
•
Bleeding per rectum
•
Tenesmus
•
Early morning diarrhoea
Abdominal examination
Abdominal examination is negative in early
cases. Occasionally, when an advanced annular growth is situated at the
rectosigmoid junction, signs of obstruction to the large intestine are likely to
be present. By the time the patient seeks advice, metastases in the liver may be
palpable. When the peritoneum has become studded with secondary deposits,
ascites results.
Rectal examination
In approximately 90 per cent of cases, the
neoplasm can be felt digitally: in early cases as a plateau or as a nodule with
an indurated base. When the centre ulcerates, a shallow depression will be
found, the edges of which are raised and everted; this, combined with induration
of the base of the ulcer, is a frequent and unmistakable finding. On bimanual
examination, it may be possible to feel the lower extremity of a carcinoma
situated in the rectosigmoid junction. After the finger has been withdrawn, if
it has been in direct contact with a carcinoma, it is smeared with blood or
mucopurulent material tinged with blood. When a carcinomatous ulcer is situated
in the lower third of the rectum, involved lymph nodes can sometimes be felt as
one or more hard, oval swellings in the extrarectal tissues posteriorly or
posterolaterally above the tumour. In females, a vaginal examination should be
performed, and when the neoplasm is situated on the anterior wall of the rectum,
with one finger in the vagina and another in the rectum, very accurate palpation
can be carried out.
Procto-sidmoidoscopy
Procto-sidmoidoscopy will always show a
carcinoma, if present — provided that the rectum is emptied of faeces
beforehand.
Biopsy
Employing biopsy forceps (Fig.
60.22) by way
of a sigmoidoscope, a portion of the edge of the tumour is removed. If
possible, another specimen from the more central part of the growth is also
obtained. Expert histological examination will not only enable the diagnosis of
carcinoma to be confirmed, but the tumour can be graded as to its relative
malignancy, although not always with complete accuracy.
Barium enema. Barium enema or, preferably, a
colonoscopy is required if possible in all patients to exclude a synchronous
tumour, be it an adenoma or a carcinoma. If an adenoma is found, it can be
conveniently snared and removed via the colonoscope. If a synchronous carcinoma
is present, the operative strategy will need changing.
When
a stenosing carcinoma is present, it may not be possible using these
investigations, especially colonoscopy, to visualise the proximal colon.
However, in view of the high incidence of synchronous tumours, it is imperative
that a colonoscopy is always performed either before or after surgical
resection.
Differential
diagnosis. When a seemingly benign adenoma
shows evidence of induration or unusual friability, it is almost certain
that malignancy has occurred, even in spite of biopsy findings to the contrary.
On the other hand, biopsy is invaluable in distinguishing carcinoma from an inflammatory
stricture or an amoebic granuloma, which
simulates a carcinoma very closely. The possibility of a neoplasm being an endometrioma
should always be entertained in patients with dysmenorrhoea. The possibility
of a carcinoid tumour in atypical
cases must be remembered. In the last four instances biopsy should establish the
correct diagnosis. The solitary ulcer syndrome
has already been alluded to above.