Colonoscopy - Marcus Daly Memorial Hospital.

Author:
Lance Pysher, MD, Radiologist
Marcus Daly Memorial Hospital
1200 Westwood Drive
Hamilton, Montana 59840
375.4428
Colonoscopy as a Screening Tool for Colorectal Cancer
Last week Doctor Jergens discussed colorectal cancer and mentioned several screening
tests for colorectal cancer, including standard colonoscopy and “virtual” (CT) colonoscopy.
This week, I am going to expand on those two screening exams
Screening tests looks for disease before people have any signs or symptoms. These tests
can help find colorectal cancer when the disease is still at an early stage and more easily
and successfully treated.
Earlier this month the American Cancer Society, the American College of Radiology, and
The US Society Task Force on Colorectal Cancer (including representatives from the
American College of Gastroenterology, the American Gastroenterological Association, and
the American Society for Gastrointestinal Endoscopy) released the first joint consensus
guideline for colorectal cancer screening. “Virtual” (CT) colonoscopy and stool DNA (sDNA)
were added to the list of recommended options.
CT Colonoscopy is a type of CT scan done to evaluate the colon for polyps and cancer.
Similar to a traditional colonoscopy, cathartic medications are given the day before the CT
to clean stool from the colon. Cleaning out the colon is the usually the most uncomfortable
part of the test. The next day, in the CT room, the colon is filled with air, and the CT takes
hundreds of pictures of the colon while spinning around the patient. This is initially done
with the person laying on their back and then repeated with the person on their stomach.
Each CT scan takes about 10 seconds on a state of the art, 64 slice, CT machine. The entire
exam takes about 15 to 20 minutes, most of which is spent getting everything set up. All the
hundreds of images are sent to a powerful computer workstation where they are combined
into a 3D view of the inside of the colon. These images can be displayed like views from a
standard colonoscopy. Around 5% of the time a polyp will be found that will require a
subsequent standard colonoscopy to perform a biopsy.
Both standard colonoscopy and CT colonoscopy have advantages and disadvantages. The

CT is faster, less expensive, does not require sedation and has less risk of injury to the
colon. The CT also can detect other abnormalities in the abdomen outside of the colon.
Some of the drawbacks of CT are that some cancers are flat and more difficult to visualize
than polyps. If a suspicious polyp is found, a standard colonoscopy will still be needed to
perform a biopsy. There are some situations in which a CT colonoscopy is preferred such
as when the colonoscopy is technically challenging, when a standard colonoscopy could
not visualize the entire colon, when a patient is either too ill to tolerate standard
colonoscopy, or on medications that would make standard colonoscopy too risky.
Because of the relative advantages/disadvantages of each exam, everyone should consult
their physician to discuss which examination is optimal for them.
Comments should be sent to Lance Pysher, MD, Radiologist, Marcus Daly Memorial
Hospital, 1200 Westwood Drive, Hamilton, MT, 59840.