Anatomical disruption and length-tension dysfunction of anal sphincter complex muscles in women with fecal incontinence

Fecal incontinence patients categorized based on anal pressure and electromyography: Anal sphincter damage and clinical symptoms

BACKGROUND

Disruption of external anal sphincter muscle (EAS) is an important factor in the multifactorial etiology of fecal incontinence (FI).

OBJECTIVES

We categorize FI patients into four groups based on the location of lesion in neuromuscular circuitry of EAS to determine if there are differences with regards to fecal incontinence symptoms severity (FISI) score, age, BMI, obstetrical history, and anal sphincter muscle damage.

METHODS

Female patients (151) without any neurological symptoms, who had undergone high-resolution manometry, anal sphincter EMG, and 3D ultrasound imaging of the anal sphincter were assessed. Patients were categorized into four groups: Group 1 (normal)-normal cough EMG (>10 μV), normal squeeze EMG (>10 μV), and normal anal squeeze pressure (>124 mmHg); Group 2 (cortical apraxia, i.e., poor cortical activation)-normal cough EMG, low squeeze EMG, and low anal squeeze pressure; Group 3 (muscle damage)-normal cough EMG, normal squeeze EMG, and low anal squeeze pressure; and Group 4 (pudendal nerve damage)-low cough EMG, low squeeze EMG, and low anal squeeze pressure.

RESULTS

The four patient groups were not different with regards to the patient's age, BMI, parity, and FISI scores. 3D ultrasound images of the anal sphincter complex revealed significant damage to the internal anal sphincter, external anal sphincter, and puborectalis muscles in all four groups.

CONCLUSION

The FI patients are a heterogeneous group; majority of these patients have significant damage to the muscles of the anal sphincter complex. Whether biofeedback therapy response is different among different patient groups requires study.

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.

Anorectal Anatomy and Function

Anatomy of pelvic floor muscles has long been controversial. Novel imaging modalities, such as three-dimensional transperineal ultrasound imaging, MRI, and diffusion tensor imaging, have revealed unique myoarchitecture of the external anal sphincter and puborectalis muscle. High-resolution anal manometry, high-definition anal manometry, and functional luminal imaging probe are important new tools to assess anal sphincter and puborectalis muscle function. Increased understanding of the structure and function of anal sphincter complex/pelvic floor muscle has improved the ability to diagnose patients with pelvic floor disorders. New therapeutic modalities to treat anal/fecal incontinence and other pelvic floor disorders will emerge in the near future.

Do resistance exercises during biofeedback therapy enhance the anal sphincter and pelvic floor muscles in anal incontinence?

AIM

To determine if a biofeedback therapy that includes concentric resistance exercise for the anal sphincter muscles can improve muscle strength/function and improve AI symptoms compared to the traditional/non-resistance biofeedback therapy.

BACKGROUND

Biofeedback therapy is the current gold standard treatment for patients with anal incontinence (AI). Lack of resistance exercise biofeedback programs is a limitation in current practice.

METHODS

Thirty-three women with AI (mean age 60 years) were randomly assigned to concentric (resistance) or isometric (non-resistance) biofeedback training. Concentric training utilized the Functional Luminal Imaging Probe to provide progressive resistance exercises based on the patient's ability to collapse the anal canal lumen. Isometric training utilized a non-collapsible 10 mm diameter probe. Both groups performed a biofeedback protocol once per week in the clinic for 12 weeks and at home daily. High definition anal manometry was used to assess anal sphincter strength; symptoms were measured using FISI and UDI-6. 3D transperineal ultrasound imaging was used to assess the anal sphincter muscle integrity.

RESULTS

Concentric and isometric groups improved FISI and UDI-6 scores to a similar degree. Both the concentric and isometric groups showed small improvement in the anal high-pressure zone; however, there was no difference between the two groups. Ultrasound image analysis revealed significant damage to the anal sphincter muscles in both patient groups.

CONCLUSIONS

Concentric resistance biofeedback training did not improve the anal sphincter muscle function or AI symptoms beyond traditional biofeedback training. Anal sphincter muscle damage may be an important factor that limits the success of biofeedback training.

Implant of Self-Expandable Artificial Anal Sphincter in Patients With Fecal Incontinence Improves External Anal Sphincter Contractility

BACKGROUND

External anal sphincter contractility significantly contributes to control the passage of stool. An artificial anal sphincter placed into the intersphincteric space is a safe and effective procedure to treat fecal incontinence, even if its mechanism of action has not been fully elucidated.

OBJECTIVE

The aim of this study was to evaluate external anal sphincter contractility changes after a self-expandable hyexpan prostheses was implanted into the intersphincteric space of the anal canal and clinical outcomes compared.

DESIGN

This was a prospective clinical study.

SETTINGS

The study was conducted at a university teaching hospital.

PATIENTS

Consecutive patients affected by fecal incontinence for at least 6 months after failure of conservative treatment were included.

INTERVENTIONS

All of the patients underwent 10-prostheses implantation and were examined preoperatively and postoperatively by endoanal ultrasound and anorectal manometry.

MAIN OUTCOME MEASURES

Fecal incontinence symptoms were assessed by severity scores. The external anal sphincter muscle tension was calculated using a specific equation.

RESULTS

Thirty-nine patients (34 women; median age = 68 y) were included in the study; no morbidity was registered. After a median follow-up period of 14 months, both the median maximum voluntary squeeze pressure and the median inner radius of the external anal sphincter significantly increased. A statistically significant increase of external anal sphincter muscle tension was detected. A decrease of any fecal incontinence symptom and an improvement in severity scores were observed at the last follow-up examination. The external anal sphincter contractility was significantly higher in patients reducing incontinence episodes to solid stool by >50% and improving their ability to defer defecation for >15 minutes.

LIMITATIONS

This was a single-center experience with a relatively small and heterogeneous sample size, patients with a potentially more severe disease because our institution is a referral center, and an absence of quality-of-life evaluation.

CONCLUSIONS

Artificial anal sphincter implantation improved the external anal sphincter muscle tension; there was a positive correlation between its increase and the clinical outcome. See Video Abstract at http://links.lww.com/DCR/B468.

IMPLANTE DE ESFNTER ANAL ARTIFICIAL AUTOEXPANDIBLE EN PACIENTES CON INCONTINENCIA FECAL MEJORA LA CONTRACTILIDAD DEL ESFNTER ANAL EXTERNO

ANTECEDENTES:La contractilidad del esfínter anal externo contribuye significativamente al control del paso de las heces. Un esfínter anal artificial colocado en el espacio interesfinteriano es un procedimiento seguro y eficaz para tratar la incontinencia fecal, incluso si su mecanismo de acción no se ha definido por completo.OBJETIVO:El objetivo de este estudio fue evaluar los cambios en la contractilidad del esfínter anal externo después de la implantación de una prótesis de hyexpan autoexpandible en el espacio interesfinteriano del canal anal y comparar los resultados clínicos.DISEÑO:Estudio clínico prospectivo.ENTORNO CLINICO:El estudio se realizó en un hospital universitario.PACIENTES:Pacientes consecutivos afectados por incontinencia fecal durante al menos 6 meses, tras fracaso de tratamiento conservador.INTERVENCIONES:Todos los pacientes fueron sometidos a la implantación de 10 prótesis, y fueron examinados pre y postoperatoriamente mediante ecografía endoanal y manometría anorrectal.PRINCIPALES MEDIDAS DE VALORACION:Los síntomas de incontinencia fecal se evaluaron mediante puntuaciones de gravedad. La tensión del músculo del esfínter anal externo se calculó mediante una formula específica.RESULTADOS:Treinta y nueve pacientes (34 mujeres; mediana de edad 68 años) fueron incluidos en el estudio; no se registró morbilidad. Después de un período de seguimiento medio de 14 meses, tanto la presión de compresión voluntaria máxima media como el radio interior medio del esfínter anal externo aumentaron significativamente. Se detectó un aumento estadísticamente significativo de la tensión del músculo del esfínter anal externo. En el último examen de seguimiento se observó una disminución de cualquier síntoma de incontinencia fecal y una mejora en las puntuaciones de gravedad. La contractilidad del esfínter anal externo fue significativamente mayor en los pacientes que redujeron los episodios de incontinencia a heces sólidas en más del 50% y mejoraron la capacidad para diferir la defecación durante más de 15 minutos.LIMITACIONES:Experiencia de un solo centro; tamaño de muestra relativamente pequeño y heterogéneo; pacientes con una enfermedad potencialmente más grave porque nuestra institución es un centro de referencia; ausencia de evaluación de la calidad de vida.CONCLUSIONES:La implantación del esfínter anal artificial mejoró la tensión muscular del esfínter anal externo; hubo una correlación positiva entre su aumento y el resultado clínico. Consulte Video Resumen en http://links.lww.com/DCR/B468.

Loop analysis of the anal sphincter complex in fecal incontinent patients using functional luminal imaging probe

Cardiac loops have been used extensively to study myocardial function. With changes in cardiac pump function, loops are shifted to the right or left. Functional luminal imaging probe (FLIP) recordings allow for loop analysis of the anal sphincter and puborectalis muscle (PRM) function. The goal was to characterize anal sphincter area-pressure/tension loop changes in fecal incontinence (FI) patients. Fourteen healthy subjects and 14 patients with FI were studied. A custom-designed FLIP was placed in the vagina and then in the anal canal, and deflated in 20-ml steps, from 90 to 30 ml. At each volume, subjects performed maximal voluntary squeezes. Area-pressure (AP) and area-tension (AT) loops were generated for each squeeze cycle. Three-dimensional ultrasound imaging of the anal sphincter and PRM were obtained to determine the relationship between anal sphincter muscle damage and loop movements. With the increase in bag volume, AP loops and AT loops shifted to the right and upward in normal subjects (both anal and vaginal). The shift to the right was greater, and the upward movement was less in FI patients. The difference in the location of AP loops and AT loops was statistically significant at volumes of 50 ml to 90 ml (P < 0.05). A similar pattern was found in the vaginal loops. There is a significant relationship between the damage to the anal sphincter and PRM, and loop location of FI patients. We propose AP and AT loops as novel ways to assess the anal sphincter and PRM function. Such loops can be generated by real-time measurement of pressure and area within the anal canal.NEW & NOTEWORTHY We describe the use of area-pressure (AP) and area-tension (AT)-loop analysis of the anal sphincters and puborectalis muscles in normal subjects and fecal incontinent patients using the functional luminal imaging probe (FLIP). There are differences in the magnitude of the displacement of the loops with increase in the FLIP bag volume between normal subjects and patients with fecal incontinence. The latter group shifts more to the right in AP and AT space.

High-frequency ultrasound imaging of the anal sphincter muscles in normal subjects and patients with fecal incontinence

INTRODUCTION

The current "gold standard" to diagnose anal sphincter morphology and disruptions utilizes low-frequency (3-9 MHz) ultrasound (US) imaging techniques that provide a general outline of the sphincter muscles, but not their microstructural details. High-frequency US transducers (7-15 MHz) have been used to study the muscle architecture (direction of muscle fascicles) in the limb muscle.

AIMS

The goal of our study was to visualize the microstructural anatomy of the anal sphincters, specifically the external anal sphincter (EAS), using high-frequency US imaging.

METHODS

Studies were conducted in asymptomatic female and male subjects and patients with fecal incontinence. US images were acquired using a low-frequency US (3-9 MHz) and high-frequency (7-15 MHz) US transducer. The latter was placed intra-anally to image the anal canal at 12, 9, 3, and 6 o'clock positions.

RESULTS

The low-frequency US images revealed the general outline of the anal sphincter muscles. On the other hand, high-frequency imaging visualized muscle fascicles and connective tissue inside the external anal sphincter (EAS). In FI patients, there was loss of muscle fascicles and alteration in the echo-intensity pattern in the region of damaged EAS suggestive of muscle fibrosis.

CONCLUSION

High-frequency ultrasound imaging is a powerful tool to visualize the microstructural details of the EAS. Our studies show that damage to the EAS muscle results in the alteration of its myoarchitecture, that is, loss of muscle fascicles and increase in the muscle connective tissue.

Gatekeeper Improves Voluntary Contractility in Patients With Fecal Incontinence

Background. Gatekeeper (GK) has shown to be safe and effective in patients with fecal incontinence (FI). We aimed to understand its mechanism of action by comparing pre- and post-implant change in the external anal sphincter (EAS) contractility. Methods. Study of EAS contractility was conducted in 16 FI females (median age = 69 years) before and after implant of 6 GK prostheses. Muscle tension (Tm), expressed in millinewtons per centimeter squared, mN(cm²)⁻¹, was calculated using the equation Tm = P(r_i)(tm)⁻¹, where P is the average maximum squeeze pressure and r_i and tm the inner radius and thickness of the EAS, respectively. The effect of a predefined set of covariates on Tm was tested by restricted maximum likelihood models. Results. Compared with baseline, despite unchanged tm (2.7 [2.5-2.8] vs 2.5 [2.2-2.8] mm; P = .31 mm), a significant increase in P (median = 45.8 [26.5-75.8] vs 60.4 [43.1-88.1] mm Hg; P = .017), and r_i (12.4 [11.5-13.4] vs 18.7 [17.3-19.6] mm; P < .001) resulted in an increase in Tm (233.2 [123.8-303.2] vs 490.8 [286.9-562.4] mN(cm²)⁻¹; P < .001) at 12 months after GK implant. Twelve-month follow-up improvements were also observed on Cleveland Clinic FI score (8-point median decrease; P = .0001), St Marks FI score (10-point median decrease; P < .0001), and American Medical Systems score (39-point median decrease; P < .0001). Restricted maximum likelihood models showed that years of onset of FI was negatively associated with change in Tm (P = .048). Conclusions. GK-related EAS compression positively influences muscle contractility by increasing r_i, with consequent increase in Tm (length-tension relationship). Further studies are needed to confirm the long-term effectiveness of GK.

Endoflip vs high-definition manometry in the assessment of fecal incontinence: A data-driven unsupervised comparison

BACKGROUND

How much anal sphincter dysfunction contributes to fecal incontinence (FI) is not clear. High-definition anorectal manometry (HDAM) and functional luminal imaging probe (Endoflip) are two new techniques to study anal sphincter function.

AIMS

The goal was to compare the diagnostic utility of HDAM and Endoflip using optimal feature(s) in each modality for FI diagnosis.

METHODS

Blinded classification was carried out on 70 female subjects (32 FI & 38 controls), using 3 prominent machine-learning clustering techniques, with 3 distance metrics. For HDAM, descriptive statistics, shape, and textural features characterizing the spatial relationship of pixels in the HDAM high-pressure zone, and for Endoflip, permutations of pressure and CSA combinations (ie, multiplication, division, or individually) at rest and squeeze were tested.

RESULTS

Intramodality: (a) Endoflip: Best clustering was obtained using the combination of the ratio of CSA over pressure at 40 and 50 mL at rest, which had significantly better specificity (P < 0.001) than using only pressure at 50 mL, no difference in sensitivity (P = 0.68). (b) HDAM: clustering using textural information at rest had significantly higher specificity compared to using only the maximal pressure at rest (P < 0.001). Intermodality: Clustering results using optimal features were not significantly different with respect to sensitivity or specificity (P > 0.05). Optimal Endoflip feature set differed significantly in specificity compared to HDAM maximal pressure at both rest (P < 0.001) and squeeze (P < 0.001).

CONCLUSION

Defective anal closure function is fairly sensitive and highly specific in diagnosing FI. Using optimal feature sets, HDAM and Endoflip perform in a similar fashion in diagnosing FI, but are not complementary.

Measuring length-tension function of the anal sphincters and puborectalis muscle using the functional luminal imaging probe

The functional luminal imaging probe (FLIP) has been used to measure the distensibility of the anal canal. We hypothesized that with increasing distension of the anal canal with FLIP there will be an increase in length of the anal sphincter muscle allowing measurement of the length-tension function of anal sphincter and puborectalis muscles (PRM). We studied 14 healthy nulliparous women. A custom-designed FLIP bag (30-mm diameter) was placed in the vagina and then in the anal canal, distended in 10-ml steps with volumes ranging from 30 to 90 ml. At each volume, subject performed maximal voluntary squeezes. Length-tension measurements were also made with a manometric probe system. Tension was calculated (pressure × radius) in Newtons per meter using a custom software program. Peak tensions at different FLIP volumes were compared with the manometric data. No change in the luminal CSA was noted at low fluid volumes; the sphincter muscles were able to fully collapse the FLIP bag within the anal canal/vagina even at rest. At larger volumes, with each squeeze there was an increase in the bag pressure and reduction in the cross-sectional area, which represents concentric contraction of the muscle. Both rest and squeeze tension increased with the increase in volume in the anal as well as vaginal canal indicating that the external anal sphincter and puborectalis muscles produce more tension when lengthened. FLIP device, which has been used to describe the distensibility of the anal canal can also provide information on the length-tension function of the anal sphincters and PRM. NEW & NOTEWORTHY The functional luminal imaging probe (FLIP) has been used to describe the distensibility of the anal canal. This report is the first to describe the use of the FLIP in the vaginal canal and the anal canal to provide information on the length-tension function of the anal sphincter and puborectalis muscles, which may provide clinicians with additional information regarding the active components of muscle contraction involved in the anal closure function.

Structure-function relationship of the human external anal sphincter

INTRODUCTION AND HYPOTHESIS

Obstetrical external anal sphincter (EAS) injury and subsequent dysfunction are leading risk factors for female fecal incontinence (FI). Limited knowledge of the EAS structure-function relationship hinders treatment optimization. We directly measured functionally relevant intrinsic parameters of human EAS and tested whether vaginal delivery alters the EAS structure-function relationship.

METHODS

Major predictors of in vivo EAS function were compared between specimens procured from vaginally nulliparous (VN, n = 5) and vaginally parous (VP, n = 7) cadaveric donors: operational sarcomere length (Ls), which dictates force-length relationship; physiological cross-sectional area (PCSA), which determines isometric force-generating capacity; fiber length (Lfn), responsible for muscle excursion and contractile velocity; and muscle stiffness. Data were analyzed using unpaired and paired t tests, α < 0.05. Results are presented as mean ± SEM.

RESULTS

The VN and VP (median parity 3) groups were similar in age and BMI. No gross anatomical defects were identified. EAS Ls (2.36 ± 0.05 μm) was shorter than the optimal Lso (2.7 μm), at which contractile force is maximal, P = 0.0001. Stiffness was lower at Ls than Lso (5.4 ± 14 kPa/μm vs 35.3 ± 12 kPa/μm, P < 0.0001). This structural design allows active and passive tension to increase with EAS stretching. EAS relatively long Lfn (106 ± 24.8 mm) permits rapid contraction without decreased force, whereas intermediate PCSA (1.3 ± 0.3 cm2) is conducive to maintaining resting tone. All parameters were similar between groups.

CONCLUSIONS

This first direct examination of human EAS underscores how EAS intrinsic design matches its intended function. Knowledge of the EAS structure-function relationship is important for understanding the pathogenesis of FI and the optimization of treatments for EAS dysfunction.

Age-related external anal sphincter muscle dysfunction and fibrosis: possible role of Wnt/β-catenin signaling pathways

Studies show an age-related increase in the prevalence of anal incontinence and sphincter muscle atrophy. The Wnt/β-catenin signaling pathway has been recently recognized as the major molecular pathway involved in age-related skeletal muscle atrophy and fibrosis. The goals of our study were to 1) evaluate the impact of normal aging on external anal sphincter (EAS) muscle length-tension (L-T) function and morphology and 2) specifically examine the role of Wnt signaling pathways in anal sphincter muscle fibrosis. New Zealand White female rabbits [6 young (6 mo of age) and 6 old (36 mo of age)] were anesthetized, and anal canal pressure was measured to determine the L-T function of EAS. Animals were killed at the end of the study, and the anal canal was harvested and processed for histochemical studies (Masson trichrome stain for muscle/connective tissue) as well as for molecular markers for fibrosis and atrophy [collagen I, β-catenin, transforming growth factor-β (TGF-β), atrogin-1, and muscle-specific RING finger protein-1 (MuRF-1)]. The L-T was significantly impaired in older animals compared with young animals. Anal canal sections stained with trichrome showed a significant decrease in the muscle content (52% in old compared with 70% in young) and an increase in the connective tissue/collagen content in the old animals. An increased protein and mRNA expression of all the fibrosis markers was seen in the older animals. Aging EAS muscle exhibits impairment of function and increase in connective tissue. Upregulation of atrophy and profibrogenic proteins with aging may be the reason for the age-related decrease in anal sphincter muscle thickness and function.NEW & NOTEWORTHY Our studies using a female rabbit model show age-related alterations in the structure and function of the external anal sphincter (EAS) muscle. We used endoluminal ultrasound to measure age-related changes in EAS muscle thickness. We employed Western blot and quantitative PCR to demonstrate age-related changes in the levels of important fibrogenic as well as atrophy markers. Our findings may have significant clinical implications, i.e., use of specific antagonists to prevent age-related EAS muscle dysfunction.

Wnt-β Catenin Signaling Pathway: A Major Player in the Injury Induced Fibrosis and Dysfunction of the External Anal Sphincter

Wnt-β catenin is an important signaling pathway in the genesis of fibrosis in many organ systems. Our goal was to examine the role of Wnt pathway in the external anal sphincter (EAS) injury-related fibrosis and muscle dysfunction. New Zealand White female rabbits were subjected to surgical EAS myotomy and administered local injections of either a Wnt antagonist (sFRP-2; daily for 7 days) or saline. Anal canal pressure and EAS length-tension (L-T) were measured for 15 weeks after which the animals were sacrificed. Anal canal was harvested and processed for histochemical studies (Masson trichrome stain), molecular markers of fibrosis (collagen and transforming growth factor-β) and immunostaining for β catenin. Surgical myotomy of the EAS resulted in significant impairment in anal canal pressure and EAS muscle L-T function. Following myotomy, the EAS muscle was replaced with fibrous tissue. Immunostaining revealed β catenin activation and molecular studies revealed 1.5–2 fold increase in the levels of markers of fibrosis. Local injection of sFRP-2 attenuated the β catenin activation and fibrosis. EAS muscle content and function was significantly improved following sFRP-2 treatment. Our studies suggest that upregulation of Wnt signaling is an important molecular mechanism of injury related EAS muscle fibrosis and sphincter dysfunction.

Implantation of SphinKeeper(TM): a new artificial anal sphincter

Introduction

A new artificial anal sphincter, SphinKeeper^TM, was devised with the aim to treat fecal incontinence (FI) by implanting specifically designed self-expandable prostheses into the intersphincteric space. Preliminary data concerning the procedure feasibility and prosthesis localization at 3 months are presented.

Methods

SphinKeeper^TM prostheses in the native state are dehydrated, thin, solid cylinder (length 29 mm, diameter 3 mm), changing their state (shorter—length 23 mm, thicker—diameter 7 mm—and softer, with shape memory) within 48 h of contact with fluids. In this study, 10 prostheses were implanted in each patient with FI under local anesthesia and under endoanal ultrasound (EAUS) guidance, into the upper-middle intersphincteric space of the anal canal by a specifically designed delivery system. EAUS was used postoperatively to assess prostheses dislocation.

Results

Ten patients (5 females; median age 58 years, range 20–75) were enrolled and treated with SphinKeeper^TM implantation. Median duration of procedure (performed by endoanal ultrasound guidance) was 40 min (range 30–45). Neither intraoperative nor postoperative complications were reported after a 3-month follow-up. In one patient, a partial dislocation of a single prosthesis was documented by EAUS, causing anal discomfort which resolved after 1 week.

Conclusion

SphinKeeper^TM can be safely implanted in patients with FI of different etiology. Implantation was well tolerated with no dislodgment of implants at 3-month follow-up.

Functional lumen imaging of the gastrointestinal tract

This nonsystematic review aims to describe recent developments in the use of functional lumen imaging in the gastrointestinal tract stimulated by the introduction of the functional lumen imaging probe. When ingested food in liquid and solid form is transported along the gastrointestinal tract, sphincters provide an important role in the flow and control of these contents. Inadequate function of sphincters is the basis of many gastrointestinal diseases. Despite this, traditional methods of sphincter diagnosis and measurement such as fluoroscopy, manometry, and the barostat are limited in what they can tell us. It has long been thought that measurement of sphincter function through resistance to distension is a better approach, now more commonly known as distensibility testing. The functional lumen imaging probe is the first medical measurement device that purports in a practical way to provide geometric profiling and measurement of distensibility in sphincters. With use of impedance planimetry, an axial series of cross-sectional areas and pressure in a catheter-mounted allantoid bag are used for the calculation of distensibility parameters. The technique has been trialed in many valvular areas of the gastrointestinal tract, including the upper esophageal sphincter, the esophagogastric junction, and the anorectal region. It has shown potential in the biomechanical assessment of sphincter function and characterization of swallowing disorders, gastroesophageal reflux disease, eosinophilic esophagitis, achalasia, and fecal incontinence. From this early work, the functional lumen imaging technique has the potential to contribute to a better and more physiological understanding of narrowing regions in the gastrointestinal tract in general and sphincters in particular.

Relationship Among Anal Sphincter Injury, Patulous Anal Canal, and Anal Pressures in Patients With Anorectal Disorders

BACKGROUND & AIMS

The anal sphincters and puborectalis are imaged routinely with an endoanal magnetic resonance imaging (MRI) coil, which does not assess co-aptation of the anal canal at rest. By using a MRI torso coil, we identified a patulous anal canal in some patients with anorectal disorders. We aimed to evaluate the relationship between anal sphincter and puborectalis injury, a patulous anal canal, and anal pressures.

METHODS

We performed a retrospective analysis of data from 119 patients who underwent MRI and manometry analysis of anal anatomy and pressures, respectively, from February 2011 through March 2013 at the Mayo Clinic. Anal pressures were determined by high-resolution manometry, anal sphincter and puborectalis injury was determined by endoanal MRI, and anal canal integrity was determined by torso MRI. Associations between manometric and anatomic parameters were evaluated with univariate and multivariate analyses.

RESULTS

Fecal incontinence (55 patients; 46%) and constipation (36 patients; 30%) were the main indications for testing; 49 patients (41%) had a patulous anal canal, which was associated with injury to more than 1 muscle (all P ≤ .001), and internal sphincter (P < .01), but not puborectalis (P = .09) or external sphincter (P = .06), injury. Internal (P < .01) and external sphincter injury (P = .02) and a patulous canal (P < .001), but not puborectalis injury, predicted anal resting pressure. A patulous anal canal was the only significant predictor (P < .01) of the anal squeeze pressure increment.

CONCLUSIONS

Patients with anorectal disorders commonly have a patulous anal canal, which is associated with more severe anal injury and independently predicted anal resting pressure and squeeze pressure increment. It therefore is important to identify a patulous anal canal because it appears to be a marker of not only anal sphincter injury but disturbances beyond sphincter injury, such as damage to the anal cushions or anal denervation.

Myoarchitectural and functional alterations in rabbit external anal sphincter muscle following experimental surgical trauma

Obstetrical trauma to external anal sphincter (EAS) is extremely common; however, its role in the development of anal incontinence is not clear. We examined the regenerative process and functional impact of experimental surgical trauma to EAS muscle in an animal model. Surgical myotomy, a craniocaudal incision extending along the entire length and thickness of the EAS, was performed in rabbits. Animals were allowed to recover, and anal pressures were recorded at weekly intervals for 12 wk using a custom-designed probe system to determine the length-tension property of EAS muscle. Animals were killed at predetermined time intervals, and the anal canal was harvested for histochemical studies (for determination of muscle/connective tissue/collagen) and sarcomere length measurement. In addition, magnetic resonance diffusion tensor imaging (MR-DTI) and fiber tracking was performed to determine myoarchitectural changes in the EAS. Myotomy of the EAS muscle resulted in significant impairment of its length-tension property that showed only partial recovery during the 12-wk study period. Histology revealed marked increase in the fibrosis (connective tissue = 69% following myotomy vs. 28% in controls) at 3 wk, which persisted at 12 wk. Immunostaining studies confirmed deposition of collagen in the fibrotic tissue. There was no change in the sarcomere length following myotomy. MR-DTI studies revealed disorganized muscle fiber orientation in the regenerating muscle. We conclude that, following experimental injury, the EAS muscle heals with an increase in the collagen content and loss of normal myoarchitecture, which we suspect is the cause of impaired EAS function.