requires the same bowel cleansing procedure as
does conventional colonoscopy.
Virtual colonoscopy does not require sedation.
For the procedure, the radiologist inserts a small
tube into the rectum for the injection of air to
open the colon for improved visualization, which
may cause discomfort that feels like intestinal gas.
Over a period of 10 to 20 minutes the CT scanner
takes sequential X-rays while the person lies on
his or her back and then STOMACH. A computer
compiles the X-rays to create three-dimensional
images of the colon.
See also BARIUM ENEMA; CANCER PREVENTION;
INTESTINAL POLYP.
colorectal cancer Malignant growths in the
COLON, most commonly in the sigmoid colon and
the RECTUM. Colorectal cancer is the second-lead-
ing cause of death due to CANCERin the United
States. However, colorectal cancer is also one of
the most preventable and, with early detection,
among the most treatable kinds of cancer. More
than 95 percent of primary colorectal cancer is
ADENOCARCINOMA, a form of cancer in which abnor-
mal but otherwise benign growths (adenomas)
become cancerous. Intestinal polyps are adenomas
that develop in the colon, growing from the
mucous membrane that lines the colon. Intestinal
polyps become more common with increasing age,
and by age 50, about half of American adults are
likely to have them.
TYPES OF POLYPS
There are two common types of colon polyps:
adenomas, which are neoplastic (abnormal
growths that have no useful function within the
body) and have malignant potential, and hyper-
plastic, which are not neoplastic and have no
malignant potential.A polyp takes 5 to 10 years to grow from micro-
scopic to detectable, and up to several decades to
become cancerous, if that is its course. People who
have no exceptional risk factors for colorectal can-
cer typically have a window of 5 to 10 years during
which the polyp’s cell structure is transitional.
Doctors consider such a polyp precancerous.
Though only a small percentage of intestinal polyps
will become cancerous, there is no way to distin-
guish those that will from those that will remain
benign. As a precaution doctors recommend
removing all intestinal polyps, which eliminates
any concerns about their potential malignancy.Symptoms and Diagnostic Path
Early colorectal cancer has few, if any, symptoms,
further emphasizing the importance of regular
screening. When present, symptoms often indicate
a cancer that is moderately to significantly
advanced and include- a change in bowel habits or the nature of bowel
movements - unexplained NAUSEA, VOMITING, DIARRHEA, or
CONSTIPATION - rectal bleeding (may be patches of dark discol-
oration or bright bleeding) - sensations of abdominal fullness or bloating
- tiredness and fatigue
- unintended weight loss
- ABDOMINAL DISTENTIONand pain
The most effective way to detect and diagnose
colorectal cancer is through regular screening pro-
cedures, which may include- DIGITAL RECTAL EXAMINATION(DRE), in which the
doctor inserts a gloved, lubricated finger into the
rectum via the ANUSto feel for abnormalities - FECAL OCCULT BLOOD TEST(FOBT), in which a labo-
ratory tests a stool sample for microscopic blood
(home-testing kits are also available) - double-contrast BARIUM ENEMA, in which the
radiologist instills barium into the lower colon
via an ENEMA, then takes X-rays as the barium
fills the rectum and sigmoid colon - sigmoidoscopy, in which the doctor inserts a
lighted viewing tube (rigid or flexible) through
the anus into the rectum and sigmoid colon,
the two segments of the colon nearest the end
of the intestinal tract and the sites where more
than half of colorectal cancers originate - COLONOSCOPY, in which the doctor inserts a
lighted, flexible viewing tube through the anus
and into the entire colon (done under sedation) - virtual colonoscopy (CT colonography)
28 The Gastrointestinal System