Practical Gastrointestinal Endoscopy

COLONOSCOPY AND FLEXIBLE SIGMOIDOSCOPY 131
and steer carefully until the tip has passed through the fluidfilled
descending colon to the splenic flexure, reached at 90·cm
(Fig. 6.48). Applying normal sigmoid straightening maneuvers
half-way round an alpha loop is a potential mistake, since this
may cause the alpha configuration to rotate back into an N-spiral
loop configuration, with much greater difficulty in reaching up
the descending colon.
A spiral loop forms in at least 40% of colonoscopies, as shown by
our 3D imager studies. However, endoscopists claiming to form
an alpha loop are shown, when they demonstrate their technique
under fluoroscopy or the 3D imager, often to be ‘pushing
through’ a complex loop, which they pass with élan—and extra
sedation because of the pain involved. A normal short or fixed
sigmoid mesocolon (from diverticular disease or any other cause
of pericolic adhesions) will not allow formation of an alpha or
spiral loop.
The alpha maneuver is the intentional formation of an alpha
or spiral loop. This was a fluoroscopically (or X-ray) monitored
routine when using early colonoscopes, and is feasible again
with the introduction of 3D magnetic imaging. The principle
of the maneuver is to maneuver the sigmoid colon into a spiral
configuration (see Fig. 6.39). If the instrument is seen to be angling
around the distal sigmoid colon towards the caecum (Fig.
6.47a), the shaft is rotated anti-clockwise at every opportunity,
using the angled tip to attempt to coax the sigmoid into a spiral
shape – with a tubular view ahead. If the colon seems long and
freely mobile, the patient is comfortable and the view is good a
spiral may have formed – so keep pushing on in, do not straighten
too soon.
90cm
Fig. 6.48–In an alpha loop the
scope runs through the fluidfilled
descending colon to the
splenic flexure at 90·cm (posterior
view).
Straightening an alpha loop
An alpha loop must be removed at some stage, because any loop
puts stress and limitation on tip angulation due to friction in
the control wires, as well as being uncomfortable for the patient.
Most colonoscopists prefer to straighten out a spiral loop as soon
as the upper descending colon is safely reached (at 90·cm) and
then to pass the splenic flexure with a straightened instrument.
However, every colonoscopist has also experienced the chagrin
of struggling to reach the descending colon and the frustration
of seeing the tip slide back when an attempt is made, too early,
to withdraw and straighten the shaft. With current very flexible
and fully angling instruments, it is occasionally better to attempt
to pass straight on into the proximal transverse colon with the
alpha or spiral loop in position rather than to straighten it at the
splenic flexure and then have difficulty with re-looping.
Spiral loop straightening is by withdrawal and strong (usually clockwise)
de-rotation. Slightly withdrawing the shaft initially reduces
the size of the loop and makes de-rotation easier, but the tip can