Practical Gastrointestinal Endoscopy

COLONOSCOPY AND FLEXIBLE SIGMOIDOSCOPY 159
The combination of an acute bend with sharp haustra and blue
coloration is characteristic of the hepatic flexure and is a useful,
but not infallible, endoscopic landmark. Pulsation of adjacent
arteries is seen in the sigmoid colon (left common iliac artery)
and transverse colon (aorta) and sometimes in the ascending
colon (right iliac). The ileo-cecal valve is the only definite anatomical
landmark in the colon, but it has been stressed already that it
is not always easy to find, and mistaken identification is possible
unless the ileum is entered or the orifice visualized.
Fluid levels can be surprisingly useful clues to localization, especially
after oral lavage. Just as the radiologist rotates the patient into
the right lateral or left lateral position to fill the dependent parts
of the colon with barium (Fig. 6.95), the endoscopist (with the patient
in the usual left lateral position) knows that the instrument
tip is in the descending colon when it enters fluid, and is in the
transverse colon when it leaves the fluid for the triangular and
air-filled lumen of the transverse colon (see Fig. 6.57). However,
a long transverse colon, when it sags down, can also contain a
large amount of fluid, so mobile colons are particularly difficult
for localization (and everything else).
Transillumination of the abdominal wall by instruments with
bright illumination (all video-endoscopes have a bright transillumination
facility) can be very helpful if other imaging modalities
are not available, but in obese patients may necessitate
a darkened room. It should be remembered that the descending
colon is so far posterior that no light is usually visible and that the
surface marking of the splenic and hepatic flexures is by transillumination
through the rib cage posteriorly. Light in the right
iliac fossa is suggestive, but not conclusive, that the instrument
is in the cecum; similar appearances can be produced if the tip
stretches and transilluminates the sigmoid or mid-transverse
colon.
Finger indentation, palpation or ballotting can be effective, particularly
in the ascending colon or cecum, where close apposition to
the abdominal wall should make the impression of a palpating
finger easily visible to the endoscopist, unless the patient is obese.
air
air
barium
barium
(a)
(b)
Fig. 6.95–Barium enema in (a) the left lateral position and (b) the right
lateral position.