The reduction in interval colorectal cancer associated with an increase in the endoscopist’s
adenoma detection rate (ADR) is well established
1
. ADR is now widely accepted as a key performance indicator in colonoscopy quality
assurance
2
. However, adenoma miss rates are reported to be as high as 20 %
3
.
Detection of adenoma during colonoscopy can be challenging because adenoma can be
located behind flexures, haustral folds and, tight angulations. Evidence is conflicting
on distal attachment devices that have recently emerged and which reportedly are associated
with an increase in ADR. There are currently three types of distal attachment devices
on the market; the transparent cap (Olympus, Tokyo); EndoCuff (Arc Medical, Leeds);
and EndoRings (EndoAid, Israel).
The transparent cap was the first distal attachment device studied for which reports
indicated increased polyp detection. It improves mucosal visualization by straightening
colonic haustra, keeping the colonic lumen open with minimal air insufflation
4
. Because the cap projects 4 mm beyond the distal end of the colonoscope, it is associated
with a learning curve.
The EndoCuff consists of soft projections that remain flat during colonoscopy insertion
and open on withdrawal to enhance mucosal inspection behind colonic folds. Unlike
the cap, the EndoCuff fits entirely over the colonoscope, without projecting beyond
the distal end of the colonoscope, so it is much easier to use. There is no reduction
in peripheral field of view
5
.
The EndoRings device is flexible silicone and consists of two layers of large, soft
circular rings that evert mucosal folds on withdrawal and allow adequate mucosal inspection.
It is designed to keep the colonoscope tip away from the bowel wall, promoting all
around colonic views
5
It is very good at flattening colonic folds and avoiding rapid withdrawal. However,
it can be challenging to introduce the EndoRings device through a narrow, angulated
sigmoid colon with diverticulosis.
In this edition of Endoscopy International Open, Marsano et al present a single-center
parallel design trial in which 126 subjects were randomized to either standard colonoscopy
(SC), cap-assisted colonoscopy (CAC) or EndoCuff-assisted colonoscopy (EAC). Colonoscopy
was performed by three experienced endoscopists in an academic unit. Study participants
were blinded to the intervention arm, but not the endoscopist. The primary outcome
of the study was ADR. The study did not report a statistically significant difference
in ADR for SC (52.4 %) versus CAC (40.5 %) versus EAC (54.8 %) (
P
= 0.37). This pattern of no statistically significant difference between treatment
arms was also seen for the remaining study outcomes; proximal ADR, distal ADR, and
sessile serrated adenoma detection rate. There was no difference in mean adenoma size
between the groups, which is probably related to the diminutive mean adenoma size
in all groups. The average withdrawal time was also similar in the SC, CAC and EAC
groups (12.9 vs 12.4 and 13.0 minutes respectively,
P
= 0.86. In this study, the pre-study ADR of each endoscopist was very high, with
a range from 43 % to 55 %. This study further supports the growing body of evidence
that device-assisted colonoscopy has no additional benefit for endoscopists with a
preexisting high ADR.
The authors should be congratulated for performing a trial comparing two distal devices
against standard colonoscopy, but the small sample size is a major limitation and
makes it difficult to draw definitive conclusions. The baseline ADR of the endoscopists
was underestimated and the potential benefit was overestimated, resulting in the calculation
of an incorrect sample size.
The current literature on efficacy of distal attachment devices is conflicting, with
the majority of studies performed in tertiary academic units with their widespread
use still to occur.
The impact of the transparent cap on PDR ± ADR appears divided, with some studies
showing an improvement
6
7
and others no benefit
8
9
. A recent meta-analysis showed an improvement in PDR with use of the cap
10
. The recent meta-analysis by Desai et al also found an improvement in proximal adenoma
detection with use of the cap
11
. A large multicenter study performed by endoscopists with a high baseline ADR (≥ 20 %)
found no significant difference in ADR (28 %) between the two study arms
8
. In a large retrospective study where trainees performed the majority of colonoscopies,
use of CAC showed a statistically significant increase in polyp and adenoma detection,
compared to SC
7
.
The transparent cap has been available longer than other distal attachment devices.
It is difficult to make sense of the literature in the current era of higher-definition
colonoscopes. Furthermore, most of the studies were performed at a time when there
was less of emphasis on colonoscopy technique.
Initial data on the efficacy of EndoCuff in improving adenoma detection showed a benefit
12
, but the subsequent evidence is inconsistent, with two large RCTs showing no additional
benefit
13
14
. Interestingly, the two studies with a negative outcome were performed by endoscopists
with a high baseline ADR, mirroring the findings by Marsano et al. A large multicenter
RCT showed a marginal (4.7 %) increase in ADR with use of the EndoCuff compared to
standard colonoscopy
15
.
A recent meta-analysis showed in improvement in ADR with EAC, with the greatest improvement
observed when used by endoscopists with low to moderate ADRs
16
.
EndoRings Is the newest distal attachment device and while an initial study showed
a significant reduction in the adenoma miss rate with the device (10.4 %) versus SC
(48.3 %)
17
, a recent large multicenter study has shown no benefit in ADR
18
. More data on the EndoRings are required before we understand its role in neoplasia
detection.
Finally, a recent multicenter trial by Rex et al showed that the EndoCuff increased
adenoma detection more than EndoRings and standard colonoscopy
19
. The proposed mechanism of action of the distal attachment devices is to improve
mucosal visualization by flattening colonic folds. It is difficult to understand how
the EndoCuff device with shorter, softer prongs can flatten colonic folds and detect
more adenomas compared to the EndoRings, with its wider rings. It is also noteworthy
that this effect was not seen in all involved centers
19
.
Data on distal attachment devices are appealing as they are safe, easy to use, and
relatively inexpensive. However, the existing literature is flawed. Studies have not
been adequately powered to draw definitive conclusions on differences between population
groups and endoscopists with varying levels of experience. The majority of data also
comes from tertiary centers in trial settings, where enthusiasm for or against their
use can introduce investigator bias. The populations studied are heterogenous, with
several studies performed on screening subjects with the greatest risk of adenoma.
The current data show a trend towards endoscopists with low to moderate ADRs gaining
the most benefit. Endoscopists with a high baseline ADR might benefit less as they
have good scope handling with excellent tip control, which allows detailed inspection
of the colonic mucosa behind folds, without slipping backwards.
We feel the distal attachments may show promise in increasing adenoma detection, but
further studies are needed to make definitive conclusions about which endoscopist
and which population group would benefit the most. The focus should still remain on
improving basic colonoscopy techniques and performing simple measures well, such as
scope handling, position change, and minimal time on withdrawal.