Practical Gastrointestinal Endoscopy

COLONOSCOPY AND FLEXIBLE SIGMOIDOSCOPY 85
High-yield indications
Anemia/bleeding/occult blood loss
Persistent diarrhea
Inflammatory disease assessment
Genetic cancer risk
Abnormality on imaging
Therapy
Low-yield indications
Constipation
Flatulence
Altered bowel habit
Pain
Table 6.1–Colonoscopy: indications and yield.
surveillance examinations and follow-up (Table 6.1). Endoscopy
is also particularly useful in the postoperative patient, either to
inspect in close-up (and biopsy if necessary) any deformity at
the anastomosis or to avoid the difficulties of achieving adequate
distension that leakage from a stoma presents for the imager.
Combined procedures (colonoscopy and virtual colography or
DCBE) have potential advantages. If carbon dioxide (CO 2
) insufflation
is used for colonoscopy or flexible sigmoidoscopy, the
colon will be absolutely deflated within 10–15·minutes and DCBE
can follow immediately. Whereas air distension insufflation is a
routine part of virtual colography, making it an ideal procedure
to combine with colonoscopy, DCBE can be made difficult if the
proximal colon is already air-filled and so difficult to coat adequately
with barium. Colonoscopic biopsies with standard-sized
forceps are no contraindication to distending the colon for DCBE
or CT colography; prior pedunculated polypectomy should not
be either. Larger biopsies or sessile polypectomy contraindicate
using distension pressure, DCBE adding the potential danger of
causing barium peritonitis—which can be fatal.
Limitations
There are limitations of colonoscopy. Incomplete examination
can be due to inadequate bowel preparation, looping, inadequate
hand-skills or an obstructing lesion, for example. A recent UK
audit showed a completion rate of 75% (much lower in some centers).
The lack of definite landmarks, unless the ileo-cecal valve is
reached and identified, means that gross errors in colonoscopic
localization are possible even for expert endoscopists. Any
colonoscopist needs to be aware of the potential for blind spots,
where it is possible to miss very large lesions, especially in the
cecum, around acute bends and in the rectal ampulla. Colonoscopic
examination, rigorously performed, can probably approach
90% accuracy for small lesions, but will never be 100%. A
‘back to back’ colonoscopy series, in which the patient was twice
colonoscoped by two expert endoscopists, showed only 15%
miss rate for polyps under 1·cm diameter. Every colonoscopist