Practical Gastrointestinal Endoscopy

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CHAPTER 6
Localization
Fig. 6.93–Pulling back the scope
shortens the colon.
70-80cm
50cm
40cm
30cm
Fig. 6.94–If the scope is in the
cecum at 70–80·cm, other anatomical
sites are predictable by
measurement.
Uncertainty in localization is one of the endoscopist’s most serious
problems, especially during flexible sigmoidoscopy or limited
colonoscopy, but even during supposed ‘total’ or complete
colonoscopy. This can lead to mistakes in judging where the
instrument has reached and therefore which maneuvers to employ.
Endoscopic errors of localization can also be catastrophic
if the surgeon is given wrong information around which to plan
a resection.
Distance of insertion of the instrument is inaccurate, although
sometimes used by inexperienced colonoscopists to express the
position of the instrument or of lesions found (‘the colonoscope
was inserted to 90·cm’, ‘a polyp was seen at 30·cm’, etc.). The
elasticity of the colon makes this information meaningless; at
70·cm the instrument may be in the sigmoid colon, in the cecum
or anywhere between. On withdrawal, however, providing no
adhesions are present and the mesenteric fixations are normal,
the colon will shorten and straighten predictably (Fig. 6.93) so
that measurement gives approximate localization. On withdrawal,
the cecum should be at 70–80·cm, the transverse colon at
60·cm, the splenic flexure at 50·cm, the descending colon at 40·cm
and the sigmoid colon at 30·cm (Fig. 6.94). The last two values
depend, of course, on the sigmoid colon being straightened. It
is sometimes difficult to convince enthusiasts for rigid proctosigmoidoscopy
that at 25·cm their instrument may still be in the
rectum, whereas the flexible colonoscope (on withdrawal) may
be in the proximal sigmoid colon. Equally, it is sometimes possible
for the colonoscope to be withdrawn to 55–60·cm when the
tip is in the cecum if the colon is mobile.
Anatomical localization is inaccurate during insertion. In almost
half the cases of a personal series the expert was wrong! In 25%,
a persistent loop (alpha or N) caused the endoscopist to judge
the tip location to be at the splenic flexure when actually it was
at the sigmoid–descending colon junction. In 20%, a mobile
splenic flexure pulled down to 40·cm from the anus, causing
the endoscopist wrongly to judge the instrument to be at the
sigmoid– descending colon junction (see Fig. 6.59). Similar inaccuracies
are demonstrated by 3D imager series.
The internal appearances of the colon can be misleading. In the sigmoid
and descending colon the haustra and the colonic outline
are generally circular (see Fig. 6.11), whereas the longitudinal
muscle straps or teniae coli cause the characteristic triangular
cross-section often seen in the transverse colon (see Fig. 6.61); the
descending colon, however, may look triangular or the transverse
colon circular in outline. Visible evidence of extracolonic viscera
normally occurs at the hepatic flexure where there is seen to be a
bluish/gray indentation from the liver, but a similar appearance
may sometimes occur at the splenic flexure or descending colon.