Imaging in colonic carcinoma is done for (1) disease detection,
(2) staging, and follow-up.
In disease detection, the traditional investigation is
a barium enema to outline the appearance of the colon. Barium
and air are introduced through a small tube inserted into
the rectum. To obtain images of different parts of the colon,
the patient is made to lie in different positions, and the
X-ray table may be tilted to various angles. For accurate
findings the colon has to be properly cleaned before the
investigation; if necessary the preparation may include
a period on a liquid or soft diet and some laxatives.
More recently, CT (virtual) colonoscopy has been proposed
as an alternative to both barium enema and colonoscopy.
This technique again requires proper cleaning of the colon
before the investigation. During the procedure, air is instilled
into the colon before the CT scans are done. The three-dimensional
images obtained aid disease assessment.
In disease staging, CT is commonly the technique of choice
for the detection of nodal involvement as well as metastasis
to the liver and lungs. Preoperative thin-section MR imaging
may also be useful for the assessment of the tumour stage
of rectal cancer and depth of extramural tumour infiltration.
It provides valuable information for identifying T3 tumours
for preoperative (neo-adjuvant) chemotherapy in patients
who are at higher risk of failure of complete excision.
In disease follow-up, CT is the technique of choice because
it allows for accurate assessment of response to treatment.
It may also be useful in distinguishing surgical from medical
causes of intestinal obstruction by identifying the cause
of the obstruction—eg, peritoneal disease or local
tumour recurrence in some patients. Although positron emission
tomography (PET) does not supplant current imaging modalities
in the routine staging and follow-up of patients with colonic
carcinoma, it may be useful in the detection of local pelvic
recurrence or even distal metastasis in patients with indeterminate
findings at CT or MRI. Since the PET tracer F-18 fluorodeoxyglucose
is taken up at a cellular level, functional images are generated
that complement the traditional anatomical images generated
through CT and MRI studies.
A) CT in a patient
with history of caecal carcinoma shows a metachronous
annular tumour in the sigmoid causing dilatation of
the bowel proximal to it |
B) CT shows presacral tumour recurrence in a patient
with colon carcinoma (A).
This was confirmed on PET-CT (B) which also reveals
metastasis to an inferior mesenteric node
which is not enlarged. (small arrow)
|
