Magnetic resonance imaging and 3-dimensional analysis of external anal sphincter anatomy

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.

Refining Approaches to Surgical Repair of Rectovaginal Fistulas

INTRODUCTION

Rectovaginal fistulas are notorious for both their morbidity and their difficulty to treat effectively. A variety of methods for repair has been described; however, there is no consensus on the ideal repair. A better understanding of the anatomical relationship of fistulas to the anal sphincter and detrusor muscles is one of the components necessary to develop an effective treatment plan for repair and preservation of sphincter mechanics.

METHODS

A review of the literature was conducted to determine the types of methods typically used by reconstructive surgeons for repair of rectovaginal fistulas. A critical clinical analysis of our series of 10 patients was performed to determine optimal strategies for and pitfalls of repair in the context of recent reports in hopes of refining surgical techniques.

RESULTS

Detailed anatomical understanding of the relationship of fistulas to the surrounding sphincter muscles is described. Etiology of the fistula and its anatomical relationship to the surrounding sphincter complex is used to help develop an algorithm for repair. Suprasphincteric fistulas will necessitate a laparotomy for repair, intersphincteric fistulas will often require muscle interposition with recreation of the vaginal and rectal walls, and low/transphincteric fistulas will require local flaps mostly for coverage and repair of the sphincter muscles.

CONCLUSIONS

Complex rectovaginal fistulas are both debilitating for the patient and extremely difficult to manage. Plastic surgeons are often involved in such cases only after previous attempts at repair have failed. The success of surgery in treating these patients with rectovaginal fistulas depends on a variety of factors. Unfortunately, the available literature describing these repairs lacks uniform guidance regarding approach to repair. Herein, we attempt to detail the possible anatomical variations of fistulas in relationship to the sphincter muscles to begin the discussion necessary for the development of an algorithm for repair that considers preservation of sphincter mechanism function.

Advance Xp® Male Sling can be an Effective and Safe Treatment for Post-Prostatectomy Stress Urinary Incontinence Also in Patients with Prior History of External Beam Radiation Therapy: A Multicentric Experience

Background. Post-prostatectomy stress urinary incontinence (PPSUI) is one of the major complaints after radical prostatectomy. Transoburator male sling (TMS) placement is indicated in persistent mild to moderate PPSUI. External beam radiation therapy (EBRT) might be a negative prognostic factor for TMS outcomes. Study objective was to analyze EBRT impact on TMS outcome. Methods. We retrospectively investigated patients submitted to TMS for PPSUI, with or without previous EBRT, in two tertiary referral centers since 2010. Objective outcome was measured through ICIQ-SF, 1-hour pad test, and pad per die and subjective improvement through PGI-I. Patients were divided according to EBRT to make in-group and between-group comparisons. Results. Patients were 56, 18 (32.1%) had previous EBRT. Median follow-up was 43.0 months (IQR: 22.3-64.0). TMS was placed at mean 18.8 months (SD 4.6) after EBRT. TMS determined a statistically significant reduction of pads, 1-hour pad test, and ICIQ-SF score (P<.05). Improvement diminished during long-term follow-up. At last follow-up, 12 patients (21.4%) used 1 safety pad, while 15 (26.8%) used 0 pads. Median PGI-I was 2 (IQR 2-3). Recorded complications were 9 (16.1%) and none exceeded Clavien-Dindo grade 2. There were no differences in outcomes, failures, and complications between groups. TMS failures were 6 (10.7%), 2 of whom in the EBRT group. Four of them (7.1%) subsequently placed an artificial urinary sphincter (AUS). Conclusion. Advance XP© placement seems effective and safe in well-selected patients complaining with PPSUI, even after EBRT. Surgical outcomes slightly deteriorate over time. Further studies are needed in these patients to assess TMS efficacy.

Management of Fecal Incontinence

Nine percent of adult women experience episodes of fecal incontinence at least monthly. Fecal incontinence is more common in older women and those with chronic bowel disturbance, diabetes, obesity, prior anal sphincter injury, or urinary incontinence. Fecal incontinence negatively affects quality of life and mental health and is associated with increased risk of nursing home placement. Fewer than 30% of women with fecal incontinence seek care, and lack of information about effective solutions is an important barrier for both patients and health care professionals. Even among women with both urinary and fecal incontinence presenting for urogynecologic care, the rate of verbal disclosure of fecal incontinence symptoms remains low. This article provides an overview of the evaluation and management of fecal incontinence for the busy obstetrician-gynecologist, incorporating existing guidance from the American College of Obstetricians and Gynecologists, the American College of Gastroenterology, and the American Society of Colon and Rectal Surgeons. The initial clinical evaluation of fecal incontinence requires a focused history and physical examination. Recording patient symptoms using a standard diary or questionnaire can help document symptoms and response to treatment. Invasive diagnostic testing and imaging generally are not needed to initiate treatment but may be considered in complex cases. Most women have mild symptoms that will improve with optimized stool consistency and medications. Additional treatment options include pelvic floor muscle strengthening with or without biofeedback, devices placed anally or vaginally, and surgery, including sacral neurostimulation, anal sphincteroplasty, and, for severely affected individuals for whom other interventions fail, colonic diversion.

Magnetic resonance imaging (MRI)-assisted laparoscopic anorectoplasty for imperforate anus: a single center experience

PURPOSE

Surgical procedures for high imperforate anus have ranged from the posterior sagittal anorectoplasty (PSARP) to laparoscopic-assisted anorectoplasty (LAARP). PSARP bisects the sphincter muscle complex, introducing muscle injury and scarring. LAARP uses a straight trocar to traverse an often non-linear sphincter muscle complex. MRI-assisted LAARP (MRI-LAARP) guides the neorectum precisely through the middle of the entire sphincter complex along its trajectory. We present our experience utilizing MRI intraoperatively during LAARP.

METHODS/PROCEDURE

Ten children underwent MRI-LAARP procedures. Intraoperative MRI was performed to delineate the sphincter complex, and to guide the advancement of an MRI-compatible needle through the center of the complex from skin to the peritoneal cavity. The remainder of the procedure was completed using the standard LAARP technique.

RESULTS

All had successful MRI needle placement through the sphincter complex. Nine patients had successful laparoscopic pull-through procedures; one was converted to open due to severe intraperitoneal adhesions. Postoperative stay averaged 5.4 ± 4.4 days. Out of the ten patients, one child had mild dehiscence of the anal anastomosis requiring revision 11 days postoperatively.

CONCLUSION

The theoretical advantage of the MRI-LAARP is placing the neorectum through the entire sphincter complex without transecting the muscle. Follow-up of these patients shows good short-term results; however, long-term follow-up will be needed to best assess sphincter and bowel function.

3D Topography of the Young Adult Anal Sphincter Complex Reconstructed from Undeformed Serial Anatomical Sections

Background

Pelvic-floor anatomy is usually studied by artifact-prone dissection or imaging, which requires prior anatomical knowledge. We used the serial-section approach to settle contentious issues and an interactive 3D-pdf to make the results widely accessible.

Method

3D reconstructions of undeformed thin serial anatomical sections of 4 females and 2 males (21–35y) of the Chinese Visible Human database.

Findings

Based on tendinous septa and muscle-fiber orientation as segmentation guides, the anal-sphincter complex (ASC) comprised the subcutaneous external anal sphincter (EAS) and the U-shaped puborectal muscle, a part of the levator ani muscle (LAM). The anococcygeal ligament fixed the EAS to the coccygeal bone. The puborectal-muscle loops, which define the levator hiatus, passed around the anorectal junction and inserted anteriorly on the perineal body and pubic bone. The LAM had a common anterior attachment to the pubic bone, but separated posteriorly into puborectal and “pubovisceral” muscles. This pubovisceral muscle was bilayered: its internal layer attached to the conjoint longitudinal muscle of the rectum and the rectococcygeal fascia, while its outer, patchy layer reinforced the inner layer. ASC contraction makes the ano-rectal bend more acute and lifts the pelvic floor. Extensions of the rectal longitudinal smooth muscle to the coccygeal bone (rectococcygeal muscle), perineal body (rectoperineal muscle), and endopelvic fascia (conjoint longitudinal and pubovisceral muscles) formed a “diaphragm” at the inferior boundary of the mesorectum that suspended the anorectal junction. Its contraction should straighten the anorectal bend.

Conclusion

The serial-section approach settled contentious topographic issues of the pelvic floor. We propose that the ASC is involved in continence and the rectal diaphragm in defecation.

A multi-compartment 3-D finite element model of rectocele and its interaction with cystocele

We developed a subject-specific 3-D finite element model to understand the mechanics underlying formation of female pelvic organ prolapse, specifically a rectocele and its interaction with a cystocele. The model was created from MRI 3-D geometry of a healthy 45 year-old multiparous woman. It included anterior and posterior vaginal walls, levator ani muscle, cardinal and uterosacral ligaments, anterior and posterior arcus tendineus fascia pelvis, arcus tendineus levator ani, perineal body, perineal membrane and anal sphincter. Material properties were mostly from the literature. Tissue impairment was modeled as decreased tissue stiffness based on previous clinical studies. Model equations were solved using Abaqus v 6.11. The sensitivity of anterior and posterior vaginal wall geometry was calculated for different combinations tissue impairments under increasing intraabdominal pressure. Prolapse size was reported as pelvic organ prolapse quantification system (POP-Q) point at point Bp for rectocele and point Ba for cystocele. Results show that a rectocele resulted from impairments of the levator ani and posterior compartment support. For 20% levator and 85% posterior support impairments, simulated rectocele size (at POP-Q point: Bp) increased 0.29 mm/cm H2O without apical impairment and 0.36 mm/cm H2O with 60% apical impairment, as intraabdominal pressures increased from 0 to 150 cm H2O. Apical support impairment could result in the development of either a cystocele or rectocele. Simulated repair of posterior compartment support decreased rectocele but increased a preexisting cystocele. We conclude that development of rectocele and cystocele depend on the presence of anterior, posterior, levator and/or or apical support impairments, as well as the interaction of the prolapse with the opposing compartment.

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

INTRODUCTION AND HYPOTHESIS

This study describes a technique to quantify muscle fascicle directions in the levator ani (LA) and tests the null hypothesis that the in vivo fascicle directions for each LA subdivision subtend the same parasagittal angle relative to a horizontal reference axis.

METHODS

Visible muscle fascicle direction in the each of the three LA muscle subdivisions, the pubovisceral (PVM; synonymous with pubococcygeal), puborectal (PRM), and iliococcygeal (ICM) muscles, as well as the external anal sphincter (EAS), were measured on 3-T sagittal MRI images in a convenience sample of 14 healthy women in whom muscle fascicles were visible. Mean ± standard deviation (SD) angle values relative to the horizontal were calculated for each muscle subdivision. Repeated measures ANOVA and post-hoc paired t tests were used to compare muscle groups.

RESULTS

Pubovisceral muscle fiber inclination was 41 ± 8.0°, PRM was -19 ± 10.1°, ICM was 33 ± 8.8°, and EAS was -43 ± 6.4°. These fascicle directions were statistically different (p < 0.001). Pairwise comparisons among levator subdivisions showed angle differences of 60° between PVM and PRM, and 52° between ICM and PRM. An 84° difference existed between PVM and EAS. The smallest angle difference between levator divisions was between PVM and ICM 8°. The difference between PRM and EAS was 24°. All pairwise comparisons were significant (p < 0.001).

CONCLUSIONS

The null hypothesis that muscle fascicle inclinations are similar in the three subdivisions of the levator ani and the external anal sphincter was rejected. The largest difference in levator subdivision inclination, 60°, was found between the PVM and PRM.

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

INTRODUCTION AND HYPOTHESIS

This study describes a technique to quantify muscle fascicle directions in the levator ani (LA) and tests the null hypothesis that the in vivo fascicle directions for each LA subdivision subtend the same parasagittal angle relative to a horizontal reference axis.

METHODS

Visible muscle fascicle direction in the each of the three LA muscle subdivisions, the pubovisceral (PVM; synonymous with pubococcygeal), puborectal (PRM), and iliococcygeal (ICM) muscles, as well as the external anal sphincter (EAS), were measured on 3-T sagittal MRI images in a convenience sample of 14 healthy women in whom muscle fascicles were visible. Mean ± standard deviation (SD) angle values relative to the horizontal were calculated for each muscle subdivision. Repeated measures ANOVA and post-hoc paired t tests were used to compare muscle groups.

RESULTS

Pubovisceral muscle fiber inclination was 41 ± 8.0°, PRM was -19 ± 10.1°, ICM was 33 ± 8.8°, and EAS was -43 ± 6.4°. These fascicle directions were statistically different (p < 0.001). Pairwise comparisons among levator subdivisions showed angle differences of 60° between PVM and PRM, and 52° between ICM and PRM. An 84° difference existed between PVM and EAS. The smallest angle difference between levator divisions was between PVM and ICM 8°. The difference between PRM and EAS was 24°. All pairwise comparisons were significant (p < 0.001).

CONCLUSIONS

The null hypothesis that muscle fascicle inclinations are similar in the three subdivisions of the levator ani and the external anal sphincter was rejected. The largest difference in levator subdivision inclination, 60°, was found between the PVM and PRM.

MRI anatomy of the anal region

PURPOSE

The aim of this study was to identify the normal anatomy of the anal region on magnetic resonance images.

METHODS

T1-weighted turbo spin-echo images of anal sagittal sections, anal coronal sections, and oblique anal transverse planes were obtained with a body coil in 60 normal volunteers (30 women and 30 men, aged 19-25 years) at rest in the supine position.

RESULTS

T1-weighted images showed fat spaces and muscles simultaneously, allowing visualization of 7 image layers, including the mucosa, submucosa, anal smooth muscle, inner (intersphincteric) space, vertical levator, outer (intersphincteric) space, and external anal sphincter. The anal smooth muscle was derived from the rectal smooth muscle, and the inner space originated from the perirectal space. The outer space lay between the vertical levator and the external sphincters. The puborectalis did not have a longitudinal portion. The deep, superficial, and SC sphincters were 3 separate muscle bundles. The perianal spaces had a complex interconnection.

CONCLUSIONS

Multiplanar body-coil MRI studies can show anorectal fat spaces and musculature simultaneously, allowing fat spaces and musculature to serve as mutual referents. The results of imaging of the anal region with this method are different from previous imaging descriptions and may provide a more accurate and systemic description of the anal region structures than was previously available.

Evaluation and treatment of anal incontinence, constipation, and defecatory dysfunction

Posterior compartment disorders include anal incontinence, constipation, and defecatory dysfunction. These disorders cause considerable morbidity, and are typically underreported by patients and undertreated by providers. The purpose of this article is outline the approach to diagnosis and treatment of anal incontinence, constipation, and defecatory dysfunction with a brief description of the nature of the problem and approaches to evaluation and diagnosis, as well as medical and surgical management.

Correlation between gross anatomical topography, sectional sheet plastination, microscopic anatomy and endoanal sonography of the anal sphincter complex in human males

This study elucidates the structure of the anal sphincter complex (ASC) and correlates the individual layers, namely the external anal sphincter (EAS), conjoint longitudinal muscle (CLM) and internal anal sphincter (IAS), with their ultrasonographic images. Eighteen male cadavers, with an average age of 72 years (range 62-82 years), were used in this study. Multiple methods were used including gross dissection, coronal and axial sheet plastination, different histological staining techniques and endoanal sonography. The EAS was a continuous layer but with different relations, an upper part (corresponding to the deep and superficial parts in the traditional description) and a lower (subcutaneous) part that was located distal to the IAS, and was the only muscle encircling the anal orifice below the IAS. The CLM was a fibro-fatty-muscular layer occupying the intersphincteric space and was continuous superiorly with the longitudinal muscle layer of the rectum. In its middle and lower parts it consisted of collagen and elastic fibres with fatty tissue filling the spaces between the fibrous septa. The IAS was a markedly thickened extension of the terminal circular smooth muscle layer of the rectum and it terminated proximal to the lower part of the EAS. On endoanal sonography, the EAS appeared as an irregular hyperechoic band; CLM was poorly represented by a thin irregular hyperechoic line and IAS was represented by a hypoechoic band. Data on the measurements of the thickness of the ASC layers are presented and vary between dissection and sonographic imaging. The layers of the ASC were precisely identified in situ, in sections, in isolated dissected specimens and the same structures were correlated with their sonographic appearance. The results of the measurements of ASC components in this study on male cadavers were variable, suggesting that these should be used with caution in diagnostic and management settings.

Correlative anatomy of the anus and rectum

An overview of the normal anatomy of the anus and rectum is provided with an emphasis on correlative imaging, including computed tomography, magnetic resonance, and ultrasound. The major clinically important structures that can be assessed with these imaging modalities are reviewed.

Posterior compartment anatomy as seen in magnetic resonance imaging and 3-dimensional reconstruction from asymptomatic nulliparas

OBJECTIVE

The objective of the study was to identify characteristic anatomical features of the posterior compartment using magnetic resonance (MR) cross-sectional anatomy and 3-dimensional (3-D) modeling.

STUDY DESIGN

Supine, static proton-density MR images of 20 nulliparas were analyzed. MR images were used to create models in a selected exemplar.

RESULTS

The compartment's upper, mid, and lower segments are best seen in the axial plane. It is bounded inferiorly by the perineal body, ventrally by the posterior vaginal wall, and dorsally by the levator ani muscles and coccyx. In the upper portion, the compartment is bordered laterally by the uterosacral ligaments, whereas in the middle portion, there is more direct contact with the lateral levator ani muscles. In the lower portion, the contact becomes obliterated because the vagina and levator ani muscles become fused to each another and to the perineal body.

CONCLUSION

The posterior compartment has characteristic anatomic features in MR cross-sectional anatomy that can be further elucidated and integrated with 3-D anatomy.

Three-dimensional transperineal sonographic characteristics of the anal sphincter complex in nulliparous women

OBJECTIVE

To explore the morphological characteristics and normal biometry of the anal sphincter complex in nulliparous Chinese women using three-dimensional (3D) transperineal ultrasound.

METHODS

3D sonographic data from 55 nulliparous Chinese women (aged 19-38 years) who had no pelvic organ prolapse and no symptoms of pelvic floor dysfunction were retrieved from an image dataset and analyzed by offline post-processing. The morphological characteristics of the external and internal anal sphincters, puborectalis muscle and perineal body were assessed in the sagittal, coronal and axial views.

RESULTS

The external anal sphincter had three sonographic components: the circular main body, a subcutaneous part and an extension portion. It was significantly thinner at 12 o'clock than at the 3, 6 and 9 o'clock positions. The internal anal sphincter was seen as dark echolucent strips of equal thickness. In the mid-sagittal view, it started from the anal verge and ended at the anorectal junction. The perineal body was an ovoid structure covering the upper margin of the external sphincter, while the puborectalis muscle was banana-shaped in the sagittal view and was located behind the anorectal junction, extending downward along the inferior margin of the posterior external sphincter extension. Sonographic characteristics of the anal sphincter complex did not vary with age, weight, height or body mass index.

CONCLUSIONS

3D transperineal ultrasound clearly demonstrates the spatial relationships of each component of the anal sphincter complex. This should allow standardized measurement of the complex for investigations of its function.

Comparison of the main body of the external anal sphincter muscle cross-sectional area between women with and without prolapse

The aim of the study was to compare the main body of the external anal sphincter (EAS) cross-sectional area (CSA) of women with and without pelvic organ prolapse. Pelvic magnetic resonance imaging (MRI) scans of 40 women were selected for analysis. Of these women, 20 had pelvic organ prolapse and 20 had normal support. Of the women with normal support, 10 had known major levator ani (LA) muscle defects and 10 had normal LA muscles. The same was true for the women with pelvic prolapse: half had major LA defects and half had no LA defects. All patients had previously completed pelvic MRI in the supine position. 3-D models of the EAS were made and CSA of the EAS perpendicular to the fiber direction were measured circumferentially at 30 degrees intervals. Univariable and multivariable analyses were performed. The mean CSA did not significantly differ between women with prolapse and normal support regardless of LA defect status (normal/-LA defect = 1.13 cm(2), prolapse/-LA defect = 0.86 cm(2), p = 0.065; normal/+LA defect = 1.08 cm(2), prolapse/+LA defect = 1.28 cm(2), p = 0.28). Women with prolapse and LA defects had a 49% larger mean muscle CSA compared to prolapse patients without LA defects (p = 0.01). This difference associated with defect status in prolapse patients was not seen in women with normal support. Women with prolapse alone had external anal sphincter CSAs that were comparable to women with normal support. However, women with both prolapse and a major levator ani defect had larger external anal sphincter CSAs compared to prolapse patients without levator ani defects.

Translabial ultrasound assessment of the anal sphincter complex: normal measurements of the internal and external anal sphincters at the proximal, mid-, and distal levels

The purpose of this study was to measure the internal and external anal sphincters using translabial ultrasound (TLU) at the proximal, mid, and distal levels of the anal sphincter complex. The human review committee approval was obtained and all women gave written informed consent. Sixty women presenting for gynecologic ultrasound for symptoms other than pelvic organ prolapse or urinary or anal incontinence underwent TLU. Thirty-six (60%) were asymptomatic and intact, 13 symptomatic and intact, and 11 disrupted. Anterior-posterior diameters of the internal anal sphincter at all levels and the external anal sphincter at the distal level were measured in four quadrants. Mean sphincter measurements are given for symptomatic and asymptomatic intact women and are comparable to previously reported endoanal MRI and ultrasound measurements.