Importance of Virtual Colonoscopy
Virtual Colonoscopy is a promising new method for detecting colorectal
polyps and cancers. Air is insufflated into a cleansed colon,
and high resolution, thinly-collimated spiral CT slices are acquired.
The two dimensional slices, as well as the post-processed "fly-through"
virtual colonoscopic images, are examined for polyps and tumors.
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.
Patient Selection
All patients who are over the age of 50 years or patients
with an increased risk of colon cancer should be screened for
colon cancer every 3 5 years. Current research on Virtual Colonoscopy
has focused on high risk patients over 50 years of age, with a
prior history of polyps, fecal occult blood, or a family history
of colon cancer. Virtual Colonoscopy has performed well in this
group of patients but Virtual Colonoscopy has not yet been tested
in a large true screening population. Currently, therefor this
technique can only be recommended in this patient group. It is
our hope that Virtual Colonoscopy will be found to be an effective
true screening technique.
Accuracy
Studies suggest a very high sensitivity and specificity (96%)
for the detection of polyps 1 cm or greater. Such polyps have
significant malignant potential. Sensitivity for polyps less than
10 mm is significantly less. Although controversy exists as to
the definition of a "significant" polyp with regard
to size, polyps < 1 cm in size have a low probability of malignancy
and the likelihood of any single lesion progressing to cancer
is also small. Many leading authorities have suggested that a
policy aimed at identifying and removing only polyps above a threshold
size, as opposed to universal polypectomy, could result in a similar
benefit in terms of mortality reduction, but at a lower risk and
cost.
Advantages
of Virtual Colonoscopy
Virtual Colonoscopy is minimally invasive, and does not carry
the low but real (1 in 1500) risk of perforation associated with
Conventional Colonoscopy. It is well tolerated by patients and
does not require sedation. It is capable of evaluating the colon
upstream from obstructing lesions that prevent passage of an endoscope.
Virtual Colonoscopy is significantly less expensive than Conventional
Colonoscopy.
Disadvantages
of Virtual Colonscopy
The dose of ionizing radiation is less than that of a conventional
abdominal CT, and is comparable to obtaining a supine and upright
plain film exam of the abdomen. Virtual Colonoscopy by CT does
not provide the same information as Conventional Colonoscopy.
Mucosal detail and color is not visible which limits the characterization
of lesions. In addition, the detection of small polyps is inferior.
As with any procedure, including Conventional Colonoscopy, there
are no guarantees that all clinically significant growths will
be detected. It should be remembered than between 10 and 20% of
all polyps, and up to 5% of colon cancers are missed, even on
Conventional Colonoscopy. Virtual Colonoscopy (like the Barium
Enema) is a diagnostic not therapeutic technique. All patients
in whom polyps are identified would need to undergo Conventional
Colonoscopy for removal.
Preparation
for Virtual Colonoscopy
The prep consists of a 24 hour liquid diet and mild over-the-counter
bowel cleansing agents.
Virtual
Colonoscopy for You the Doctor
It is one thing for doctors to recommend colon screening for their
patients, it is another thing for doctors themselves (their spouses
and/or parents) to have their own colons checked. Now that an
accurate, quick, and safe test is available it is even less excusable
to avoid or delay "clearing your colon." Colon screening
by Virtual Colonoscopy , at least for a doctor and his family,
should be as basic and instinctive as a mammogram for her and
a PSA for him once a certain age is reached. The same goes for
parents of younger physicians. Moreover, unlike the breast or
prostate cancer, where the disease is already a cancer when discovered,
in the case of colorectal neoplasms, what is being sought is the
precursor polyp in order to interrupt the gradual progression
from polyp to cancer.
Most authorities now accept a screening strategy for average risk,
asymptomatic individuals that calls for colon screening every
3-5 years. A simple and ideal recommendation would be to have
your colon screened at least once in your lifetime, perhaps on
your 60th birthday. This could be done by any combination of a
structural or Total Colon Exam which traditionally has meant Conventional
Colonoscopy or Air Contrast Barium Enema. The availability of
Virtual Colonoscopy splits the difference between these two standard
techniques in terms of the trade offs between cost, risk, and
accuracy and should be high on the "to do" list of physicians
(and their spouses). Give yourself and your spouse a once in a
lifetime birthday present, say at age 60 - an appointment for
a Virtual Colonoscopy.
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