Patient
Information
Virtual colonoscopy is a new method that allows doctors to look
at the large bowel (colon) to detect polyps and cancers. Polyps
are small growths in the colon that may become cancerous if
they are not removed. Virtual colonoscopy is a recently developed
technique that uses a CT scanner and computer virtual reality
software to look inside the body without having to insert a
long tube (Conventional Colonoscopy) into the colon or without
having to fill the colon with liquid barium (Barium Enema).
Research performed at Boston University and elsewhere has shown
that Virtual Colonoscopy is better able to see polyps than Barium
Enema and is nearly as accurate as Conventional Colonoscopy.
In addition, most patients report that the Virtual Colonoscopy
technique is more comfortable than either Barium Enema or Conventional
Colonoscopy.
Why is it important?
Colorectal cancer (CRC) is a leading cause of cancer-related
death in the United States. In 1999, approximately 140,000
cases of colon cancer will be diagnosed in the United States,
and 60,000 patients will die of the disease. Colon cancer
can be prevented if polyps are discovered and removed early.
Tumors, masses of abnormal cells, take years to develop. Initially,
a cell from the colon starts to multiply abnormally and
forms a benign (non-cancerous) polyp, which can remain
harmless for a long time before becoming an aggressive cancer.
Polyps, when detected, can be removed preventively. Nevertheless,
individuals at greatest risk of developing colorectal cancer
remain largely underscreened. This is due, in part, to poor
public awareness and acceptance of current screening techniques.
What are the current methods used to detect polyps?
There are several tests that are used to try and detect polyps.
Several government agencies as well as the American Cancer
Society recommend that patients undergo a test that allows the
doctor to see the entire colon at age 50 and then every
three to five years. Currently there are two accepted methods
for seeing the entire colon; Conventional Colonoscopy and the
Barium Enema. Other tests like the Flexible Sigmoidoscope
or which can only see a small portion of the large bowel
(colon) are considered inferior tests. Conventional Colonoscopy
is associated with increased risk and cost. Conventional Colonoscopy
is unable to see the entire colon in 1 out of ten people. In
addition, Conventional Colonoscopy may cause an injury of the
colon (tear or perforation) in one of 1500 patients. Medication
given into the vein (intravenous sedation) is usually required
to make the exam bearable and therefore patients cannot resume
normal activities immediately after the test. The introduction
of a safe, noninvasive, and effective method of detecting colorectal
polyps and cancers has obvious appeal and has been the reason
researchers at the Center for Virtual Colonoscopy at Boston
Medical Center are pursuing evaluation of Virtual Colonoscopy.
How is Virtual Colonoscopy done?
Virtual colonoscopy uses a standard computed tomography (CT
or CAT scan) of the abdomen, which allows radiologists
(special physicians with advanced training in x-ray imaging)
to create pictures on the computer that look similar to
those seen by Conventional Colonoscopy. Patients need a
cleansing preparation of their bowel prior to the test. The
day of the test, they come to the radiology department
for a CT scan. The actual virtual colonoscopy procedure will
begin by having a small flexible rubber tube placed in
the rectum, so that air can be introduced. A CAT scan is
then performed while patients lie comfortably on their back
and then on their stomach. The total time required for
the study is approximately 10-20 minutes. Because sedation is
not required, patients are free to leave the CT suite
immediately without the need for observation or recovery.
Patients can resume normal activities immediately after the
procedure and can eat, work or drive without a delay. Doctors
(radiologists) analyze the CT data to detect colon polyps or cancers.
Is it painful?
When air is introduced in the colon some patients experience minimal
temporary abdominal cramping or "gas pains". An
intravenous injection of a widely used medicine to relax the bowel can
also be given to help reduce gas pains, but this is usually not
necessary.
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