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 Referral
Letter
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Bulletin Board
VIRTUAL COLONOSCOPY - HAS IT ARRIVIED?
I attended an overview of developments of Virtual Colonoscopy at
the Digestive Diseases Week, San Diego in May.
Virtual Colonoscopy has potential major advantages in surveillance
and screening for polyps and cancer. What are the problems?
Technology
Present spiral CT or slower MR scanning can provide images of the
entire colon in 15 to 20 seconds, that is a single breath hold.
A Radiologist's assessment of the 2D slices or three-dimensional
images produced by computer manipulation may take between 30 and
60 minutes. Although automated fly throughs are being developed.
Patient preparation
(a) Colon cleasing is still required and is a significant deterrent
to patient compliance. However, computer faecal deletion techniques
are being explored.
(b) Gaseous distension is necessary and uncomfortable for the patient.
Accuracy of results
For 6 - 9 mm polyps, sensitivity compared with present colonoscopy
is about half (50 to 80%) and for sessile polyps, which have a greater
malignant potential, is even worse.
In summary, in its present state of development, Virtual colonoscopy
is not an appropriate technique particularly for surveillance or
screening because of:
(a) Colon preparation and distension are still required limiting
patient compliance.
(b) More expensive than colonoscopy due to
(1) equipment and (2) radiological interpretation.
Overall, real colonoscopy still remains the "gold standard"
and retains both its diagnostic and therapeutic application.
PETER GRAY
M.B.B.S. (Melb), F.R.C.S., (Ed), F.R.A.C.S. M.B. B.S. F.R.A.C.P.
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