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Many of the symptoms which bring a patient to the doctor for exclusion of
colorectal cancer are caused by simple benign conditions. In most cases the
result of the consultation is reassurance and simple instructions accompanied
by a prescription.
In other cases the physician prefers to proceed to further investigations. Some
or all of the investigations listed below may be chosen.
a. Colonoscopy
This is considered the “golden standard” investigation of the colon and rectum.
It allows excellent visualization of the internal lining of the bowel (the “mucosa”)
and photographs can be taken. More importantly, biopsies of suspicious areas
can be taken. Also colonoscopy can allow removal of polyps at the same time:
this is called “polypectomy” and is achieved by using a snare with electric
current.
Colonoscopy is performed with the aid of the colonoscope which is a flexible
instrument consisting of optic fibres. The flexible glass fibres transmit the light
and images and record them on digital video.
There is no need for general anaesthetic, only sedation and analgesia in the
form of an injection is required. Colonoscopy is done as a “day case” and no
hospitalisation is necessary.
However, colonoscopy is a relatively invasive procedure for two reasons.
Firstly, “full bowel preparation”, a very thorough cleaning of the colon with
powerful laxatives is required the day before. Some elderly or frail patients may
be unsuitable for this intense treatment.
Secondly, colonoscopy has a, low but real, risk of complications.
Bowel perforation can occur, particularly at the time of a polypectomy or if the
bowel has diverticula. If this occurs emergency surgery is required, usually with
good results.
Bleeding can happen after polypectomy or if the patient is on anticoagulant
drugs (which thin the blood). In most cases bleeding is managed conservatively
but surgery may occasionally be required.
Drug reactions to the sedation/ analgesia injections can rarely occur, therefore
the colonoscopy is always performed under monitoring of the pulse and
breathing.
All the above risks are extremely rare, usually less than 1:500 -1:1,000 cases
therefore the colonoscopy remains a safe test with more than 99.8% safety.
b. Flexible sigmoidoscopy
This is a very similar investigation to the colonoscopy but there are two main
differences. Because flexible sigmoidoscopy examines only the left side of the
colon there is no need for “full bowel preparation” and there is a much lower risk
of complications.
It is chosen in cases where the doctor believes that the problem is likely to be
located in the left side of the colon.
c. Barium enema
This is series of x rays taken after an enema of contrast followed by insufflation
of the colon with air. It gives fairly good images of the colon but it is not so good
for the rectum, therefore it has to be complemented with rigid or flexible
sigmoidoscopy. It requires “full bowel preparation” like colonoscopy. The main
deficiency of this investigation is that it does not have the potential for biopsies
or polypectomy at the same time.
d. CT Scan
CT scan is a widespread method of imaging the whole of the body and the
abdomen and gives excellent images of solid organs and structures. However it
is not so good in imaging hollw organs such as the bowel, therefore it is not a
first line investigation for bowel problems. However when a cancer is found CT
scan is essential in the “staging” process, i.e. to identify how advanced the
cancer is.
e. CT Colonography or “Virtual Colonoscopy”
Recently CT scan has been reinforced with virtual reality technology and can
produce reconstructed virtual images of the bowel which are quite accurate.
This technology is progressing very fast and it is likely that in a few years CT –
Colonography may replace a large number of colonoscopies. The main benefit
of this would be the avoidance of the risks of colonoscopy.
f. MRI Scan
Magnetic Resonance scanning gives images that are comparable to those of
CT scanning. However MRI is superior in imaging the rectum and it is used when
a cancer of the rectum is found for the”staging” process.
g. Laboratory tests
several blood tests are required when investigating for colorectal cancer. Those
are Full Blood Count (to check for anaemia), Biochemistry (to check for
abnormal function of all the organs of the body which might get affected by
advanced cancer), Tumour Markers (CEA, CA 19-9) which show whether there
is a cancer in the body etc.
Stool tests can be useful in order to detect occult bleeding (Faecal Occult Blood
tests or FOB) and to exclude infection.
Recently a new inflammatory marker in the stools, Faecal Calprotectin, is being
studied (the Department of Gastroenterology at King's College Hospital is
among the pioneering research departments in this area). This marker is
elevated in inflammation of the bowel and in cancer.
For a description of the staging systems for colorectal cancer please click on
the link.
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Investigations