Comparative study of anal acoustic reflectometry and anal manometry in the assessment of faecal incontinence

Current and future perspectives on the utility of provocative tests of anal sphincter function: A state-of-the-art summary

BACKGROUND

The maintenance of fecal continence depends upon coordinated interactions between the pelvic floor, anorectum, and anal sphincter complex orchestrated by central and peripheral neural activities. The current techniques to objectively measure anorectal function rely on fixed diameter catheters placed inside the anal canal with a rectal balloon to obtain measurements of anal resting and squeeze function, and rectal compliance. Until recently it had not been possible to measure the distensibility of the anal canal, or in other words its ability to resist opening against an increasing pressure, which has been proposed as the main determinant of a biological sphincter's function. Anal acoustic reflectometry (AAR) and the functional lumen imaging probe (FLIP) are two novel, provocative techniques that dynamically assess the anal sphincter complex under volume-controlled distension. In doing so, both provide information on the viscoelastic properties of the anal canal and offer new insights into its function.

PURPOSE

This review details the current and potential future applications of AAR and FLIP and highlights the unanswered questions relevant to these new technologies.

Relationship between anal functional lumen imaging probe (EndoFLIP®) results and the clinical presentation of faecal incontinence

AIM

Faecal incontinence (FI) subtypes (urge, passive, mixed) are linked to the physiopathological mechanism of FI. Previous studies have failed to demonstrate a consistent relationship between FI subtype and anal sphincter dysfunction. Our aim was to evaluate the relationship between anal sphincter function, assessed using the new EndoFLIP® technology, and FI subtype.

METHOD

Patients referred for FI were prospectively enrolled between October 2015 and May 2021 in a registry, and data were retrospectively examined. Each patient underwent a clinical assessment as well as three-dimensional high-resolution or water-perfused anorectal manometry, anal EndoFLIP®, and anorectal electrophysiological and endoanal ultrasound tests. The results of the investigations were compared across FI subtypes.

RESULTS

The cohort included 133 patients, 54 (41%) of whom met the criteria for urge FI, 40 (30%) for passive FI and 39 (29%) for mixed FI. The resting anal distensibility index (DI) at 50 ml of distension was significantly lower in patients with urge FI than in patients with passive FI (p = 0.04). At rest, a DI at 50 ml of distension ≥7.3 mm²  mmHg^-1 and a DI at 40 ml of distension <1.3 mm²  mmHg^-1 were associated with the passive and urge FI subtypes, respectively, with poor discriminatory power (an accuracy of 0.49 compared with 0.33 for random assignment). There were no differences in anorectal manometry, endoanal ultrasound or electrophysiological test results among the urge, passive and mixed FI subgroups (all p > 0.05).

CONCLUSION

The anal sphincter DI using the EndoFLIP® system displayed poor predictive performance in distinguishing among FI subtypes.

Comparison of clinical and paraclinical characteristics of patients with urge, mixed, and passive fecal incontinence: a systematic literature review

PURPOSE

Two subgroups of fecal incontinence (FI) are described in literature and used in clinical practice. However, the pertinence of this classification of FI is still unknown as there are no clear established guidelines. To a better understanding, we performed a systematic review to characterize the different types of FI (active, passive, or mixed) on the basis of clinical presentation and complementary explorations.

METHODS

This systematic literature review was performed in reference to recommendations for systematic review using PRISMA guidelines without date restriction, until May 2020. This systematic review was performed without temporal limitation using MEDLINE-PubMed, Cochrane Library, and Google Scholar databases.

RESULTS

Six hundred nine unique citations were identified from all the databases combined. Of those, 21 studies met the inclusion criteria, with 8 retrospective observational studies and 13 prospective observational studies. There was a lack of homogeneity in definitions of passive and urge (active) FI among studies. Prevalence of passive and urge FI was respectively of 4.0-5.0 and 15.0-35.0%. Clinical characteristics, physical examination, and endoanal imaging were not evaluated in most studies. In anorectal manometry, maximal squeeze pressure was higher in passive FI subgroup in most studies and results regarding maximal resting pressure remain discordant. There seemed to be no difference regarding first sensation volume and maximal tolerable volume among subgroups. A few studies evaluated pudendal terminal nerve motor latency with no difference among subgroups.

CONCLUSION

There is a lack of well-conducted prospective studies comparing the different subtypes of FI with validated definitions in both clinical and paraclinical examinations.

A novel method for measurement of the recto-anal inhibitory reflex using anal acoustic reflectometry

AIM

The recto-anal inhibitory reflex (RAIR) is currently measured using manometry catheters, which potentially distort the anal canal. Anal acoustic reflectometry (AAR) is considered to be a catheter-free technique and primarily measures the function of the internal anal sphincter. We sought to determine if RAIR could be measured using AAR.

METHOD

Patients aged 18 and over attending the hospital for investigation of pelvic floor dysfunction were included. AAR parameters were obtained before (prerectal distension) and after (postrectal distension) inflation of a rectal balloon catheter with 100 ml of air. Minimum opening pressure (Op, cmH₂ O), opening elastance (Oe, cmH₂ O/mm² ), closing pressure (Cp, cmH₂ O), closing elastance (Ce, cmH₂ O/mm² ) and hysteresis (Hys, %) were recorded. The presence of RAIR was defined by a reduction of prerectal distension Op by 20% or more.

RESULTS

Thirty-two patients were included, 26 of whom were women. The mean age of patients was 57.5 years (SD 11.3 years). Nine patients had faecal incontinence, six patients had obstructive defaecation and 17 patients had both. RAIR was seen in 30/32 patients. The mean reduction in Op was 58.8% (range -59.18% to 100%). Three patients had 100% reduction. Comparison of pre- and post-RAIR parameters showed a significant difference in Op (34.44 vs 15.41, P < 0.0001), Oe (1.39 vs 1.1, P = 0.004), Cp (20.06 vs 8.00, P < 0.0001) and Ce (1.31 vs 1.13, P < 0.0001) but not Hys (39.71 vs 39.90, P = 0.88).

CONCLUSION

We describe a novel method for the measurement of RAIR. Rectal distension appears to alter resting pressure and the resistance of the anal canal to opening and closing, with complete inhibition of the sphincter complex in three patients.

Placement of a fine-bore rectal balloon catheter in the anal canal does not affect anal sphincter pressures: improving our understanding of physiological function with anal acoustic reflectometry

AIM

The recto-anal inhibitory reflex (RAIR) is currently measured using anorectal manometry catheters, which may distort the anal canal. Anal acoustic reflectometry (AAR) is considered a catheter-free technique for evaluating the physiological function of the anal canal; however, it has yet to be used to elicit the RAIR. For the RAIR to be measured with AAR, the effect of placing an additional rectal balloon catheter on the measured AAR parameters needs to be investigated: that is the aim of this work.

METHOD

Patients aged over 18 years attending hospital for the investigation of pelvic floor disorders were included. AAR parameters were obtained before and after a rectal balloon catheter was placed alongside the AAR catheter. The following parameters were measured: opening pressure (Op, cmH₂ O), opening elastance (Oe, cmH₂ O/mm² ), closing pressure (Cp, cmH₂ O), closing elastance (Ce, cmH₂ O/mm² ), hysteresis (Hys, %), squeeze opening pressure (SqOp, cmH₂ O) and squeeze opening elastance (SqOe, cmH₂ O/mm² ).

RESULTS

Thirty-five patients were included in the analysis, of whom 28 were women. The median age was 58 years. Comparison of median AAR parameters before and after catheter placement showed no significant difference: Op (36.36 vs 33.42, P = 0.09), Oe (1.27 vs 1.39, P = 0.19), Cp (18.62 vs 19.73, P = 0.13), Ce (1.2 vs 1.28, P = 0.33), Hys (41.08 vs 40.11, P = 0.17), SqOp (81.85 vs 81.65, P = 0.93) and SqOe (1.44 vs 1.49, P = 0.55).

DISCUSSION

Placement of a rectal balloon catheter alongside the AAR catheter has no significant effect on the measured AAR parameters. The results of this study add to the fundamental basic science and understanding of the physiological function of the anal canal.

Tools for fecal incontinence assessment: lessons for inflammatory bowel disease trials based on a systematic review

BACKGROUND

Fecal incontinence is a disabling condition affecting up to 20% of women.

OBJECTIVE

We investigated fecal incontinence assessment in both inflammatory bowel disease and non-inflammatory bowel disease patients to propose a diagnostic approach for inflammatory bowel disease trials.

METHODS

We searched on Pubmed, Embase and Cochrane Library for all studies on adult inflammatory bowel disease and non-inflammatory bowel disease patients reporting data on fecal incontinence assessment from January 2009 to December 2019.

RESULTS

In total, 328 studies were included; 306 studies enrolled non-inflammatory bowel disease patients and 22 studies enrolled inflammatory bowel disease patients. In non-inflammatory bowel disease trials the most used tools were the Wexner score, fecal incontinence quality of life questionnaire, Vaizey score and fecal incontinence severity index (in 187, 91, 62 and 33 studies). Anal manometry was adopted in 41.2% and endoanal ultrasonography in 34.0% of the studies. In 142 studies (46.4%) fecal incontinence evaluation was performed with a single instrument, while in 64 (20.9%) and 100 (32.7%) studies two or more instruments were used. In inflammatory bowel disease studies the Wexner score, Vaizey score and inflammatory bowel disease quality of life questionnaire were the most commonly adopted tools (in five (22.7%), five (22.7%) and four (18.2%) studies). Anal manometry and endoanal ultrasonography were performed in 45.4% and 18.2% of the studies.

CONCLUSION

Based on prior validation and experience, we propose to use the Wexner score as the first step for fecal incontinence assessment in inflammatory bowel disease trials. Anal manometry and/or endoanal ultrasonography should be taken into account in the case of positive questionnaires.

Continuous vs stepwise anal acoustic reflectometry: An improved technique for physiological measurement of anal sphincter function?

BACKGROUND

Anal acoustic reflectometry (AAR) is a technique for measuring the physiological profile of the anal canal, primarily the internal anal sphincter. Evaluation of a new continuous method, recently developed for the urethra, would enable its future application for investigation of rectal reflexes.

METHODS

Patients aged 18 and over with fecal incontinence (FI) were included. Stepwise AAR parameters were compared with continuous opening pressure (Op, cmH₂ O), opening elastance (Oe, cmH₂ O/mm² ), closing pressure (Cp, cmH₂ O), closing elastance (Ce, cmH₂ O/mm² ), hysteresis (Hys, [%]), squeeze opening pressure (SqOp, cmH₂ O), and squeeze opening elastance (SqOe, cmH₂ O/mm² ). Vaizey incontinence and Manchester Health Questionnaire scores were also collected.

RESULTS

Thirty-two patients, 26 females were analyzed. Median age: 60 (range, 32-75). Median AAR parameters of Op (37.50 vs 35.15, P = .031), Oe (1.31 vs 0.84, P < .0001), Ce (1.11 vs 0.88, P < .0001), Hys (37.75 vs 19.04, P < .0001), and SqOe (1.27 vs 1.06, P = .005) were significantly higher with the continuous method. Cp (22.70 vs 27.22, P = .003) is lower and SqOp (96.87 vs 59.47, P = .71) not significantly different. The continuous technique had superior repeatability between cycles for all AAR parameters except Oe, which was equivalent and continuous SqOp had a stronger negative correlation with Vaizey score than stepwise (-0.46, P = .009 vs -0.37, P = .038).

CONCLUSIONS

The differences seen between the two techniques are likely to be related to the rate of stretch. The continuous technique appears to represent a more physiological measurement of anal sphincter function than the stepwise technique particularly in the assessment of voluntary squeeze function.

Methodologic Validation of a Faster Pelvic Floor Test: Two Randomized Studies in Anal Acoustic Reflectometry

BACKGROUND

Anal acoustic reflectometry investigates the opening and closing function of the anal canal using reflected sound waves to measure a cross-sectional area at different pressures. Anal acoustic reflectometry is reliable and repeatable, distinguishes between continence and incontinence and between subgroups of incontinence, correlates with symptom severity, and does not distort the anal canal during investigation.

OBJECTIVE

The purpose of this study was to validate anal acoustic reflectometry methodology by asking 2 questions: can anal acoustic reflectometry be used alongside manometry (order study) and can anal acoustic reflectometry be performed faster (filling study). The secondary aim was to assess the response of the anal canal to stretch using anal acoustic reflectometry.

DESIGN

This research included 2 prospective randomized studies.

SETTINGS

The study was conducted at a tertiary referral center.

PATIENTS

Patients undergoing investigation for fecal incontinence were included.

INTERVENTION

For the order study, patients were prospectively randomized to anal acoustic reflectometry, manometry, 2-minute rest and then manometry, anal acoustic reflectometry, or vice versa. For the filling study, patients were prospectively randomized to fast rate anal acoustic reflectometry (5 cm H2O/1 s), manometry, 2-minute rest and then manometry, normal rate anal acoustic reflectometry (5 cm H2O/3 s), or vice versa.

MAIN OUTCOME MEASURES

The primary outcome was no difference in anal acoustic reflectometry or manometry variables. Demographic and clinical data were recorded.

RESULTS

The order study included 30 patients with a median age of 63 years (range, 30-84 y); 77% were women. No difference was found among all of the variables of anal acoustic reflectometry and manometry regardless of which test was performed first. The filling study included 50 patients with a median age of 62 years (range, 30-78 y); 80% were women. No difference was found between fast and normal rates of anal acoustic reflectometry and manometry in any order.

LIMITATIONS

This study was limited by its comparison with water-perfused manometry.

CONCLUSIONS

Anal acoustic reflectometry and manometry can be performed at the normal or fast rate of anal acoustic reflectometry in any order. A fast rate of anal acoustic reflectometry did not augment the response of the anal canal to stretch as measured by anal acoustic reflectometry and manometry. This study validates a faster anal acoustic reflectometry technique and vindicates previous data. See Video Abstract at http://links.lww.com/DCR/A821.

Use of Anal Acoustic Reflectometry in the Evaluation of Men With Passive Fecal Leakage

BACKGROUND

Men with passive fecal leakage represent a distinct clinical entity in which the pathophysiology remains unclear. Standard anorectal investigations fail to demonstrate consistent abnormalities in this group. Anal acoustic reflectometry is a new test of anal sphincter function with greater sensitivity and discriminatory ability than conventional anal manometry.

OBJECTIVE

The aim of this study was to determine whether men with fecal leakage have an abnormality in anal sphincter function that is detectable by anal acoustic reflectometry.

DESIGN

This was an age-matched study of continent and incontinent men.

SETTINGS

The study was conducted at a university teaching hospital.

PATIENTS

Male patients with isolated symptoms of fecal leakage were recruited. Anal acoustic reflectometry, followed by conventional anal manometry, was performed. Results were then compared with those from an age-matched group of men with no symptoms of anal incontinence or anorectal pathology.

MAIN OUTCOME MEASURES

Variables measured with anal acoustic reflectometry and anal manometry in the incontinent and continent men were compared.

RESULTS

Thirty subjects were recruited, of whom 15 were men with fecal leakage and 15 were continent men. There was a significantly higher incidence of previous anorectal surgery in the men with leakage. The anal acoustic reflectometry variables of opening and closing pressure were significantly lower in leakers compared with continent subjects (p = 0.003 and p = 0.001). Hysteresis was significantly greater in the male leaker group (p = 0.026). No difference was seen in anal manometry.

LIMITATIONS

With a larger sample size, the effect of previous anorectal surgery and the presence of an anal sphincter defect could be clarified.

CONCLUSIONS

Anal acoustic reflectometry is a sensitive test of anal sphincter function and, unlike anal manometry, can discriminate male leakers from continent subjects. An identifiable abnormality has been detected using anal acoustic reflectometry, which may further our understanding of the pathogenesis in this group.

Anal acoustic reflectometry predicts the outcome of percutaneous nerve evaluation for faecal incontinence

BACKGROUND

Sacral nerve stimulation (SNS) is effective for some patients with faecal incontinence. Before insertion of a costly implant, percutaneous nerve evaluation (PNE) is undertaken to identify patients likely to report success from SNS. The aim of this study was to determine whether variables of anal sphincter function measured by anal acoustic reflectometry (AAR) could predict the outcome of PNE for faecal incontinence.

METHODS

Women with faecal incontinence undergoing PNE were recruited. AAR, followed by anal manometry, was performed on the day of surgery, immediately before PNE. The outcome of PNE was determined by bowel diary results and incontinence severity score. Patients with a successful PNE outcome were compared with those with an unsuccessful outcome; logistic regression analysis was used to identify any independent predictors of success.

RESULTS

Fifty-two patients were recruited, of whom 32 (62 per cent) had a successful PNE outcome and 20 (38 per cent) an unsuccessful outcome. The AAR variable opening pressure was significantly greater in patients who subsequently had a successful PNE result compared with the pressure in patients who did not (28 versus 17 cmH2 O; P = 0·008). No difference was seen in the manometric equivalent, maximum resting pressure. Opening pressure was an independent predictor of success with an odds ratio of 1·08 (95 per cent confidence interval 1·01 to 1·16; P = 0·018).

CONCLUSION

AAR is a sensitive test of sphincter function and can identify differences between patients who respond to PNE and those who do not. Opening pressure is an independent predictor of success in PNE, and may be of value in the selection of patients for this expensive treatment option.