Technical Reports

Rigid or Flexible Sigmoidoscopy in Colorectal Clinics?Appraisal Through a Systematic Review and Meta-analysis

Nasir Zaheer Ahmad, FRCSI, and Aftab Ahmed, FRCSI

Abstract

Aim: Rigid sigmoidoscopy is sometimes performed at first presentation in colorectal clinics. We assessed thefeasibility of flexible sigmoidoscopy in similar situations by comparing it with rigid sigmoidoscopy as a firstinvestigative tool.Methods: The Medline, Embase, and Cochrane databases were searched for randomized and non-randomizedclinical trials comparing the usefulness of rigid and flexible sigmoidoscopy. The risk difference (RD) andweighted mean difference (WMD) were calculated for the cancers/abnormalities detected and discomfort as-sociated with the procedure, respectively. The standard mean difference (SMD) was calculated for the depth ofexamination and duration of the procedure.Results: Flexible sigmoidoscopy had a significantly higher rate of detection of cancers and total abnormalities(RD of 0.020 and 0.138 and 95% confidence interval [CI] of 0.006–0.034 and 0.077–0.200, respectively), and rigidsigmoidoscopy caused significantly more patient discomfort (WMD of 0.981 and 95% CI of 0.693–1.269). Flexiblesigmoidoscopy provided significantly greater depth of examination (SMD of 3.175, 95% CI of 2.397–3.954), andrigid sigmoidoscopy required less time (SMD of - 1.601, 95% CI of - 2.728 to - 0.474).Conclusions: Flexible sigmoidoscopy is a better investigative tool in colorectal clinics than the rigid sigmoid-oscopy. Implementation of this idea can help in early diagnosis at first presentation and can certainly expeditethe management of colorectal malignancies.

Introduction

The use of simple anal and rectal specula to investigatethe lower gastrointestinal tract dates back to the times of

Pompeii.1 There was very little change in these instrumentsuntil 1895, when Howard Kelly, a professor of gynecology andobstetrics at The Johns Hopkins Hospital, Baltimore, MD,demonstrated the superiority of his 30-cm rigid sigmoido-scope.2 His apparatus used atmospheric distension and re-quired a head mirror to reflect daylight for bowel illumination,as modern insufflation and illumination techniques were notyet available. His colleagues further modified his design topermit examination of the lower 20–25 cm of bowel. In 1968,Bergein Overholt pioneered the design of a flexible sigmoi-doscope for deeper examination and better patient tolerance.3

Its efficacy was recognized, and other endoscopists used itwith favorable results. Flexible sigmoidoscopy started toflourish in the late 1960s, leading to the development of currentcolonoscopes.

Rigid sigmoidoscopy is an integral technique in some co-lorectal clinics and is accepted as a valuable form of investi-gation in diseases of the colon and rectum. Because of thelimited examination achieved by rigid sigmoidoscopy relativeto the distribution of colorectal lesions, this technique onlyallows for exclusion of more distally located pathologies anddoes not necessarily give a clue about the proximal lesions.4,5

Although flexible sigmoidoscopy is expected to overcome thelimitations of rigid examination, its role in colorectal clinicshas not been acknowledged to date.6

The flexible technology in gastrointestinal endoscopy hasfailed to eliminate the use of rigid sigmoidoscopy in colorectalclinics. The continued use of rigid instrument as a primaryinvestigation over the last two decades in the absence of rel-evant supporting literature necessitated a systematic review.7

This study was conducted to assess the feasibility of flexiblesigmoidoscopy in colorectal clinics by comparing the effec-tiveness of rigid and flexible techniques in the investigation ofcolorectal symptoms.

Letterkenny General Hospital, Letterkenny, County Donegal, Ireland.Some of these results were presented in a poster at the XXth Waterford Surgical October Meeting, October 16, 2010.

JOURNAL OF LAPAROENDOSCOPIC & ADVANCED SURGICAL TECHNIQUESVolume 22, Number 5, 2012ª Mary Ann Liebert, Inc.DOI: 10.1089/lap.2012.0087

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Patients and Methods

A search of the Medline, Cochrane, and Embase databasesusing the key words ‘‘rigid,’’ ‘‘flexible,’’ and ‘‘sigmoidoscopy’’was performed to identify publications comparing flexibleand rigid sigmoidoscopy. The search was limited to clinicaltrials, randomized controlled trials, comparative studies,congresses, controlled clinical trials, and evaluation studies.The search was not constrained by language or year of pub-lication. An additional search for articles in press and con-ference presentations was also performed. A manual search ofreferences was carried out to recruit as many eligible studiesas possible. Two independent reviewers assessed these pub-lications for inclusion in the meta-analysis, and any dis-agreements were resolved by discussion and consensus.

Quality assessment

The included publications were evaluated using the qualityappraisal checklist of Downs and Black.8 This checklist isbased on assessment of reporting, external validity, bias, andconfounding and is composed of 27 points with a maximumpossible score of 33.

End points

Our primary end point was rate of detection of colorectalcancer within the reach of either rigid or flexible sigmoidos-copy. The rate of detection of other findings like polyps, in-flammatory bowel disease, or diverticulosis with bothtechniques was also compared. The depth of examination,discomfort associated with the procedure, and duration of theprocedure were evaluated as secondary end points.

Study selection

Because of the lack of relevant literature, both randomizedand non-randomized clinical trials comparing rigid andflexible sigmoidoscopy were considered for inclusion in thisanalysis. Studies comparing rigid and flexible sigmoidos-copy in symptomatic and asymptomatic patients attendingcolorectal clinics for investigations of colorectal symptoms orscreening were selected. To be eligible for inclusion in themeta-analysis, a study had to compare at least one of thechosen primary or secondary end points in a prospectivefashion. Trials with a known diagnosis of cancer or otheranal and perianal pathologies were not considered for in-clusion.

Data extraction

Data were extracted on patient’s demographics, indicationsfor sigmoidoscopy, expertise of operators, associated inves-tigations, and technical details by one of the reviewers andcounterchecked by the other. An attempt to contact the au-thors was made only if the missing data affected the quanti-tative analysis.

Statistics

Data on end points and other technical details were ex-tracted using a self-designed pro forma. The decision onwhether to use fixed or random effects for meta-analysis wasbased on the heterogeneity among the studies. Significantheterogeneity (P < 0.1) warranted the use of a random effect

model, and vice versa. Dichotomous data were pooled forevents and sample size for prospective studies. The risk dif-ference (RD) was calculated for the number of cancers andother abnormalities detected. The weighted mean difference(WMD) was calculated for the discomfort associated with theprocedure. For other continuous data, such as duration ofprocedure and depth of examination, the standard meandifference (SMD) was calculated. The end points were mea-sured on different scales in different studies. For the purposeof the meta-analysis, the mean and standard error of the mean(SEM) values were calculated for dichotomous and continu-ous data. Meta-analysis was done for randomized and non-randomized trials separately, and the results were combinedto check the overall effect. Forest plots were generated, andpublication bias was checked qualitatively by means of afunnel plot and quantitatively by the classic fail-safe Nmethod. A sensitivity analysis was performed by excludingindividual studies and checking the impact on the overallanalysis. Comprehensive Meta-Analysis version 2 softwarewas used for statistical calculations.

Results

A Medline search revealed 32 relevant studies, whereassearches of Embase and Cochrane found four and five studies,respectively. Manual Internet searching found three morepublications. This constituted 41 publications addressing therole of sigmoidoscopy in clinical practice. For the purpose ofthis meta-analysis, 10 publications comparing rigid and flex-ible sigmoidoscopy were selected.9–18 In cases where the sameauthors had more than one publication suitable for inclusion,the study with the greater number of patients was included inthe analysis. Four of the trials were randomized, and the re-mainders were non-randomized clinical trials.

As the search strategy did not include a language restric-tion, one article in German and one in Italian were foundsuitable for meta-analysis. Both were translated to Englishbefore data extraction. The selection and exclusion of trialsfor meta-analysis were performed in accordance with thePRISMA: Preferred Reporting of Items for Systematic Re-views and Meta-analysis statement (Fig. 1).19

The quality assessment method of Downs and Black8 wasused for evaluation of the quality and risk of bias. The averagescore of included studies in this analysis was 16 (standarddeviation 2). The areas of poor scoring were deficient expla-nation and adjustment for principal confounders, missingactual probability values with lack of appropriate statisticalmethods, and absence of description of a source populationfrom which the study samples were selected.

No attempts were made to blind the patients because of thephysical nature of the investigation, and those who measuredthe outcome of intervention could not be blinded either. Theinvestigative nature of the intervention did not require a pe-riod of follow-up to elicit the results, and consequently therewas no question of losses to follow-up. The assessment ofquality and risk of bias with other study characteristics aredisplayed in Table 1.

There were a total of 3915 patients. In four of the trialspatients were divided into two groups depending on whichintervention they received, whereas in the rest of the trialsboth interventions were carried out one after the other. Rigidsigmoidoscopy was performed on 2854 patients, and flexible

480 AHMAD AND AHMED

sigmoidoscopy was performed on 2947 patients. Commonindications included bleeding from the rectum, altered bowelhabits, surveillance, screening, and positive findings on bar-ium enemas. The rate of diagnosis of colorectal cancer andother abnormalities is shown in Table 2.

The mean and SEM for the number of cancers detected withrigid and flexible sigmoidoscopy were 2.89 (SEM 0.93) and10.33 (SEM 3.41), respectively. The corresponding figures fortotal abnormalities detected were 45.67 (SEM 18.67) and114.67 (SEM 50.23), respectively (Table 2). In the calculation oftotal abnormalities, non-polypoid and non-carcinomatouspathologies, such as inflammatory bowel disease and diver-ticular disease, were also recorded. The inclusion of thesepathologies did not distort the results of this analysis. Thegreater number of lesions detected with flexible sigmoidos-copy was partly due to the increased length of the instrumentand partly because of increased maneuverability around thebends. The RD was calculated for rigid and flexible sig-moidoscopy using a random effect model, which favoredflexible sigmoidoscopy (Figs. 2 and 3).

The discomfort associated with the procedure was measuredat different scales in different studies. The available data werestandardized at a scale of 0 to 10 for the level of discomfort, andmean and standard deviation values were estimated. WMDwas calculated for comparison of rigid and flexible sigmoid-oscopy using the random effect model. The overall effect fa-vored the use of a flexible sigmoidoscope (Fig. 4).

The extent of the distance examined from the anal vergewas significantly greater with a flexible scope. This applied to

both 35-cm and standard 60-cm flexible sigmoidoscopes. Themean and SEM values for rigid and flexible scopes were 18.90(SEM 0.699) and 44.27 (SEM 3.466), respectively. The SMDwas calculated to compare both modalities using a randomeffect model. The results strongly supported the use of flexiblesigmoidoscopy (Fig. 5).

As expected, the duration of the procedure was signifi-cantly shorter with a rigid sigmoidoscope than with a flexibleone. Rigid sigmoidoscopy took about half as much time tocomplete the procedure (mean – SEM, 3.70 – 0.79 minutes forrigid and 6.83 – 1.58 minutes for flexible). The SMD was cal-culated using a random effect model for both techniquesand showed significantly shorter procedure duration with therigid sigmoidoscope (Fig. 6).

Sensitivity analysis

Sensitivity analysis was performed by excluding individualstudies and checking the impact on the overall results. Theanalysis was conducted for all end points. No change in the neteffect was observed after removing any study from the analysis.

Publication bias

Publication bias was checked qualitatively with a funnelplot for the pathologies detected (Fig. 7) and was confirmedarithmetically with the classic fail-safe N method.20 Thenumbers of unpublished null studies necessary to abolishsignificance from the analysis were 51, 705, 120, 1277, and1976 for cancer detection, total abnormalities, discomfort,

FIG. 1. PRISMA flow chart.

FLEXIBLE SIGMOIDOSCOPY IN COLORECTAL CLINICS 481

depth of examination, and duration of procedure, respec-tively. A symmetrical funnel plot and high fail-safe N valueswere reassuring in reporting the findings of our analysis andobviously suggested a limited possibility of publication bias.

Discussion

The common symptoms prompting investigation in colo-rectal clinics include rectal bleeding, altered bowel habits,tenesmus, abdominal pain, and anemia. Surveillance after

bowel surgery and screening for colorectal cancer in high-riskpatients represent a major indication for diagnostic bowelexamination. The recent guidelines published by the Ameri-can College of Gastroenterology recommend either colono-scopy or flexible sigmoidoscopy for the screening of colorectalcancer.21 The usefulness of flexible sigmoidoscopy in inves-tigations of colorectal symptoms has long been accepted. Theabsolute need for flexible sigmoidoscopy was established bythe fact that a selective policy of performing this test to in-vestigate rectal bleeding missed colorectal neoplasia in sev-eral patients.22 A selective approach with respect to age hasbeen suggested by some endoscopists.23,24 Other colorectalsymptoms, depending on their severity, also warrant imme-diate investigations.

Adequate bowel preparation is an important determinantof the success of both rigid and flexible sigmoidoscopy.25 Forrigid sigmoidoscopy two self-administered suppositorieshave been shown to improve the view, whereas a singlephosphate enema is considered adequate for flexible sig-moidoscopy.26–28 Rigid sigmoidoscopy performed in theclinic would not necessarily give a clue of underlying pa-thology. Flexible sigmoidoscopy, on the other hand, has beendemonstrated to reduce the mortality from colorectal cancerwhen performed only once in the older age group.29 A similarsort of preparation for both techniques and the value of once-only flexible examination could support the case for flexiblesigmoidoscopy in colorectal clinics.

Table 1. Characteristics of Included Randomized and Non-randomized Trials

Study Country Patients Scorea Barium enema Position End points

Bohlman et al.9 United States 120 15 All Inverted AbnormalitiesDiscomfortDepth of examDuration

Marks et al.10 United States 1012 20 Selective Knee chest/Sims AbnormalitiesDiscomfortDepth of exam

Montori et al.11 Italy 200 14 Pre NG AbnormalitiesWinnan et al.12 United States 342 16 No Knee chest/Sims Abnormalities

DiscomfortDepth of examDuration

Farrands et al.13 United Kingdom 227 13 All NG AbnormalitiesDepth of exam

Spencer et al.14 United States 1007 16 All NG AbnormalitiesDepth of examDuration

Grobe et al.15 United States 71 15 Pre Knee chest AbnormalitiesDiscomfortDepth of examDuration

Classen et al.16 Germany 114 17 No Forward tilted AbnormalitiesDiscomfortDepth of examDuration

Wilking et al.17 United States 293 16 Selective Knee chest/Sims AbnormalitiesDepth of exam

Winawer et al.18 United States 529 19 No NG DiscomfortDepth of examDuration

aScore is the quality assessment score of Downs and Black.8 The maximum score was 33.NG, not given; Sims, left-lateral position.

Table 2. Diagnosis of Cancer

and Other Abnormalities

Rigid sigmoidoscopy Flexible sigmoidoscopy

Study Abnormalities Cancers Abnormalities Cancers

Bohlman et al.9 15 (12.5) 1 (0.8) 55 (45.8) 3 (2.5)Marks etal.10 158 (15.6) 6 (0.6) 501 (49.5) 16 (1.6)Montori et al.11 32 (32.0) 8 (8.0) 44 (44.0) 16 (16.0)Winnanet al.12 14 (4.1) 1 (0.3) 55 (16.1) 3 (0.9)Farrands et al.13 16 (7.0) 3 (1.3) 118 (51.9) 27 (11.9)Spencer et al.14 126 (25.2) 5 (1.0) 150 (29.5) 23 (4.5)Grobe et al.15 8 (11.2) 1 (1.4) 19 (26.7) 1 (1.4)Classen et al.16 35 (30.7) 0 (0) 56 (49.1) 1 (0.8)Wilking et al.17 7 (7.0) 1 (1.0) 34 (17.6) 3 (1.5)

The values in parentheses are percentages.

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The diagnostic yield is undoubtedly dependent on thedepth of examination. This meta-analysis compared two dif-ferent lengths of instruments. The longer flexible scopes ob-viously diagnosed more lesions compared with the shorterrigid scopes because of their greater depth of examination.One could argue that diagnostic yield cannot be comparedbetween scopes of different lengths. By comparing rigid andflexible sigmoidoscopy, this meta-analysis actually addressedthe feasibility of using flexible sigmoidoscopy in the sameoutpatient settings where rigid sigmoidoscopy was being

practiced. Moreover, flexible sigmoidoscopy was found todiagnose more lesions even within the length of bowel that isreachable with rigid sigmoidoscopy.9,15,17 This finding wasfurther supported by trials that used shorter flexible sigmoi-doscopes.15,16,18 Findings missed by flexible sigmoidoscopyhave rarely been reported.12

The discomfort associated with the procedure was reporteddifferently across trials. Some trials measured discomfortsubjectively, whereas others reported it indirectly as patientacceptance of the procedure. Rigid sigmoidoscopy was

FIG. 2. Meta-analysis of cancers detected. CI, confidence interval.

FIG. 3. Meta-analysis of total abnormalities detected.

FLEXIBLE SIGMOIDOSCOPY IN COLORECTAL CLINICS 483

associated with more discomfort and consequently less ac-ceptance of the procedure. Bowel wall stretching and de-creased maneuverability contributed to greater patientdiscomfort. In spite of a high level of discomfort experiencedby patients during rigid sigmoidoscopy, this technique hasbeen reported as a well-tolerated and cost-effective proce-dure.30 Flexible sigmoidoscopy, on the other hand, causesminimal discomfort and gives better depth of examination insimilar conditions.31 The pain and discomfort associated withflexible sigmoidoscopy can be reduced further by using an

upper endoscope for colorectal cancer screening.32 Alter-native instruments for rigid examination to reduce discomfortare not known.

Complications related to the procedures were not describedin all the trials. Perforation of the bowel is the most seriouscomplication. The rate of colonic perforation with flexiblesigmoidoscopy is 0.03%, and that with colonoscopy is 0.1%.33

Colonic perforation has also been reported with the use ofrigid sigmoidoscopes with unknown actual incidence.34 Thedegree of experience of the operator, the age of the patient, and

FIG. 4. Meta-analysis of the discomfort associated with the procedure.

FIG. 5. Meta-analysis of depth of examination.

484 AHMAD AND AHMED

the complexity of the procedure have been held responsible forcomplications.35 There was 1 case of bowel perforation afterflexible sigmoidoscopy in the studies included in this meta-analysis, whereas no complication related to rigid sigmoid-oscopy was reported. Although the complications cannot beoverlooked yet, they were not significant enough to dismissthe idea of flexible technique in the clinics.

Rigid sigmoidoscopy also carries a risk of cross-contaminationbetween patients. This applies to both disposable and reus-able sigmoidoscopes. The reusable components of a dispos-able rigid sigmoidoscope, such as the insufflation bellows andthe light head, were found to be the source of contaminatingorganisms. Culture of enteric organisms in these reusable

parts of rigid sigmoidoscopes confirmed the hypothetical riskof cross-contamination from patient to patient and labeled theexamination as a non-sterile procedure.36 Flexible sigmoido-scopes, in comparison, undergo a stringent sterilization pro-cess that prevents the risk of contamination.37 The theoreticalrisk of cross-contamination with rigid sigmoidoscopy couldlimit its use as a routine investigation.

The understanding of the anatomical position of colorectalpathologies is important. The accurate localization of rectalcancers affects further management. Colonoscopic localiza-tion of rectosigmoid or rectal cancers differs from the mea-surements obtained with a rigid sigmoidoscope and isbelieved to be more accurate.38 Similarly, the distance from

FIG. 6. Meta-analysis of duration of procedure.

FIG. 7. Assessment of publication bias.

FLEXIBLE SIGMOIDOSCOPY IN COLORECTAL CLINICS 485

anal verge to rectal cancer estimated with magnetic resonanceimaging seems to be slightly lower than with rigid sigmoid-oscopy; this has implications for determining the role ofneoadjuvant chemoradiotherapy.39 Rigid sigmoidoscopy isalso highly sensitive in the evaluation of penetrating injuriesof the lower gastrointestinal tract, which aids in determiningappropriate treatment options.40 Rigid sigmoidoscopy is asimple and cost-effective way of localizing rectal pathologies,but the initial diagnostic role is better dealt with a flexibleinstrument.

Because of the lack of available literature, this analysis useda combination of randomized and non-randomized trials. Theavailable randomized trials were of low quality because ofmissing descriptions of the randomization method. Descrip-tions of dropouts and demographics were also missing inmost of the trials. The non-randomized trials were also ofmoderate quality. Sigmoidoscopies performed to confirmprior barium enema findings could have caused a degree ofbias in some of the trials. These constituted unavoidablelimitations in this meta-analysis. The strengths of this studyincluded a thorough literature search, sensitivity analysis,assessment of publication bias, and the use of random effectmodels to overcome heterogeneity among the studies.

In conclusion, the present systematic review commemoratesan old message, which was disregarded by some cliniciansin the past. The evidence from randomized and non-randomized clinical trials clearly defies the use of rigid sig-moidoscopy. One would really like to know whether rigidsigmoidoscopy is an ultimate test or whether it is just thebeginning of a cascade of investigations. If no vital informa-tion is overlooked by skipping this preliminary investigation,why not switch over to a more comprehensive test? It isagreed that neither rigid nor flexible sigmoidoscopy is acomplete examination, but the limitations particularly relatedto rigid sigmoidoscopy justify a radical changeover to flexiblesigmoidoscopy as a primary investigation in colorectal clinics.Although the economic aspects of this transition require moreprobing, this would certainly have a positive impact on theearly diagnosis of colorectal cancer.

Acknowledgments

Thanks to Mr. Neville Couse, Consultant Colorectal Sur-geon at Letterkenny General Hospital, for his guidance inwriting the final manuscript.

Disclosure Statement

No competing financial interests exist.

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Address correspondence to:Nasir Zaheer Ahmad, FRCSI

7 Hazelwood DriveKnocknamona

Letterkenny, County DonegalRepublic of Ireland

E-mail: nasirzahmad@gmail.com

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