Anatomy of the anal canal and perianal structures as defined by phased-array magnetic resonance imaging

Imaging the levator ani and the puborectalis muscle: implications in understanding regional anatomy, physiology and pathology

Purpose:To review the findings of recent dynamic imaging of the levator ani muscle in order to explain its function during defecation. Historical anatomical studies have suggested that the levator ani initiates defecation by lifting the anal canal, with conventional dissections and static radiologic imagery having been equated with manometry and electromyography.Materials and methods:An analysis of the literature was made concerning the chronological development of imaging modalities specifically designed to assess pelvic floor dynamics. Comparisons are made between imaging and electromyographic data at rest and during provocative manoeuvres including squeeze and strain.Results:The puborectalis muscle is shown distinctly separate from the levator ani and the deep external anal sphincter. In contrast to conventional teaching that the levator ani initiates defecation by lifting the anus, dynamic illustration defecography (DID) has confirmed that the abdominal musculature and the diaphragm instigate defecation with the transverse and vertical component portions of the levator ani resulting in descent of the anus. Current imaging has shown a tendinous peripheral structure to the termination of the conjoint longitudinal muscle, clarifying the anatomy of the perianal spaces. Planar oXy defecography has established patterns of movement of the anorectal junction that separate controls from those presenting with descending perineum syndrome or with anismus (paradoxical puborectalis spasm).Conclusions:Dynamic imaging of the pelvic floor (now mostly with MR proctography) has clarified the integral role of the levator ani during defecation. Rather than lifting the rectum, the muscle ensures descent of the anal canal.

A Prospective Observational Study of the Classification of the Perineum and Evaluation of Perineal Repair at the Time of Posterior Colporrhaphy

OBJECTIVE

The aim of this prospective observational study was to obtain a better understanding of the anatomy and to classify the observed different perineal presentations at the time of posterior colporrhaphy and to describe specific surgical techniques used.

METHODS

To classify the observed perineal findings, the Pelvic Organ Prolapse Quantification System with a newly introduced additional measurement of the perineal ridge (PR) was taken intraoperatively and postoperatively in 121 consecutive women undergoing posterior colporrhaphy. Dependent on the preoperative classification of the perineum as being normal (type 1), deficient (type 2), or with a PR (type 3), a specific surgical repair was performed for each type of perineal presentation.

RESULTS

The perineal presentations were categorized into 3 defined groups. Type 1 (normal perineum) was seen in 40%, type 2 (deficient perineum) in 13%, and type 3 (PR) in 47%. A type 1 correlates with prior cesarean section (P = 0.29), a type 2 correlates with prior vaginal delivery (P = 0.05), and type 3 perineum with prior pelvic floor surgery (P < 0.0001). When perineal type-specific surgical techniques were performed, the perineal body length increased postoperatively in type 2 (P < 0.05), decreased in type 3 (P < 0.05), and remained unchanged in those with type 1 defects.

CONCLUSIONS

This study demonstrates that the perineal region can be clearly defined into 3 categories. The distinct perineal presentation correlates with the previous gynecological history. With a specific perineal repair at the time of posterior colporrhaphy, the perineal anatomy can be restored in the short term.

Clinical Significance of 2 Deep Posterior Perianal Spaces to Complex Cryptoglandular Fistulas

BACKGROUND

Confusion exists regarding the clinical significance of the deep posterior intersphincteric space and deep postanal space to complex perianal fistulas.

OBJECTIVE

The purpose of this study was to assess the clinical significance of the 2 deep posterior perianal spaces and to describe in detail the courses of posterior complex cryptoglandular fistula extensions.

DESIGN

This was a retrospective study. MRI-based characteristics of selected perianal fistulas were independently evaluated by examiners who focused on lesions in these 2 spaces and were blinded to each other's findings.

SETTINGS

This study was conducted in the colorectal surgery and radiology departments of a large university teaching hospital in China.

PATIENTS

Included in the study were patients who underwent pelvic MRI for posterior perianal fistula between October 2012 and December 2014.

MAIN OUTCOME MEASURES

The occurrence rates of these 2 deep perianal space lesions in posterior cryptoglandular fistulas were determined.

RESULTS

A total of 513 primary posterior cryptoglandular fistulas were identified in 508 patients, including 167 deep posterior intersphincteric space lesions (32.6%) and 23 deep postanal space lesions (4.5%). Of those, 173 fistulas (33.7%) were evaluated as complex. The former and latter spaces were involved in 79.2% (137/173) and 13.3% (23/173) of posterior complex fistulas. Compared with deep postanal space lesions, deep posterior intersphincteric space lesions were more common in cases with high transsphincteric or suprasphincteric fistulas (80.1% vs 15.8%), synchronous multiple transsphincteric fistulas (82.4% vs 20.6%), horseshoe-like fistulas (85.5% vs 14.5%), and supralevator fistulas (93.5% vs 16.1%). Similar incidences were also seen in cases with ischioanal-involved horseshoe-like fistulas (75.0% vs 25.0%).

LIMITATIONS

This study was limited by its retrospective nature.

CONCLUSIONS

The deep posterior intersphincteric space is more likely than the deep postanal space to be involved in complex cryptoglandular fistulas and is likely to play a more important role in the management of complex cryptoglandular fistulas.

The comparison of CT fistulography and MR imaging of perianal fistulae with surgical findings: a case-control study

PURPOSE

The purpose of this study was to evaluate the diagnostic efficacies of CT fistulography and MRI, in the diagnostic work-up of perianal fistula patients.

MATERIALS AND METHODS

All 41 patients who were included in the study (36 males and 5 females, with an average age of 41 years) underwent CT fistulography and MRI examinations prior to surgery. The fistula characteristics obtained from these examinations were compared with the surgical findings. The comparative results were evaluated by means of the Kappa analysis method.

RESULTS

CT fistulography predicted the correct perianal fistula classification in 30 (73.1%) of the 41 patients, whereas MRI correctly defined fistula classification in 38 (92.7%) of these patients (the K values were 0.621 and 0.896, respectively; with p < 0.001). CT fistulography depicted 29 secondary extensions in 16 patients, whereas MR imaging revealed 28 secondary extensions in 15 patients. A substantial agreement was found between surgical findings and two modalities (K value was 0.789 and 0.793 for CT fistulography and MRI, respectively, with a p value < 0.001). In terms of locations of internal openings, CT fistulography was able to detect the locations in 28 patients (68.2%), whereas MRI was more successful in this aspect, with a number of 35 patients (85.3%). Granulation tissues, inflammation and edema around the fistula, abscesses, and fistular wall fibrosis were also evaluated.

CONCLUSION

CT fistulography and MRI have different advantages in the diagnosis of perianal fistulas. A good command of knowledge concerning the issue may be a key factor in modality decision.

Synchronized functional anal sphincter assessment: maximizing the potential of anal vector manometry and 3-D anal endosonography

BACKGROUND

Understanding the association between structure and function is vital before considering surgery involving anal sphincter division. By correlating three-dimensional anal endosonography (AES) and three-dimensional anal canal vector volume manometry (VVM), this study details a method to produce measurements of both sphincter length and pressure leading to identification of the functionally important areas of the anal canal. The aim of this study was to provide combined detailed information on anal canal anatomy and physiology.

METHODS

Twelve males and 12 nulliparous females with no bowel symptoms underwent VVM (using a water-perfused, eight-channel radially arranged catheter) and AES.

KEY RESULTS

The synchronization of AES and VVM identified that the majority of rest and squeeze anal pressure is present in the portion of the anal canal covered by both anal sphincters. Nearly, 20% of overall resting anal pressure is produced distal to the caudal termination of the internal anal sphincter. Puborectalis accounts for a significantly greater percentage volume of pressure in females both at rest and when squeezing, though the total volume of pressure is not significantly greater.

CONCLUSIONS AND INFERENCES

The majority of resting and squeezing pressure and the least asymmetry, in both sexes, is in the portion of the anal canal covered by external anal sphincter. In females, the external anal sphincter is shorter and a proportionately longer puborectalis accounts for a greater percentage of pressure. Sphincter targeted fistula surgery in females must be performed with special caution. A protective role for puborectalis following obstetric anal sphincter injury is suggested.

Perineal body anatomy seen by three-dimensional endovaginal ultrasound of asymptomatic nulliparae

AIM

The perineal body (PB) plays an important role in supporting the pelvic floor and the posterior vaginal wall, but its attachments and relationships are still debated. This study aimed to assess the normal anatomy of the PB using high-resolution three-dimensional endovaginal ultrasound (3D-EVUS) in asymptomatic nulliparae.

METHOD

To validate the identification of perineal structures, 3D-EVUS was initially performed on nulliparous cadavers. Fresh frozen pelves were prepared and echogenic structures thought to be the PB, the external anal sphincter, the superficial and deep transverse perineii, pubovaginalis, puboperinealis, puboanalis, puborectalis and iliococcygeus muscles were tagged with biopsy needles, and marked with indigo carmine dye for localization during dissection. In the second part of the study, consecutive asymptomatic nulliparae were prospectively imaged with the same ultrasound modality. Interrater reproducibility was assessed off-line from stored 3D US volumes using a standardized technique.

RESULTS

Five fresh frozen pelves and 44 asymptomatic nulliparae were assessed with 3D-EVUS. The PB was seen as an ovoid structure of mixed echogenicity between the rectum and vagina. It appeared to be divided into a superficial level, in contact with the external anal sphincter, the bulbospongiousus and the superficial transverse perineii muscle and a deep level, in contact with puboperinealis and puboanalis muscles. Interobserver repeatability was excellent for the measurements of PB height [intraclass correlation coefficient (ICC) 0.927], PB depth (ICC 0.969) and PB width (ICC 0.932).

CONCLUSION

The PB is divided into two levels with different anatomical relationships with the pelvic floor muscles. 3D-EVUS yields reproducible assessment of this complex structure.

Clinical symptoms related to anal sphincter defects and atrophy on external phased-array MR imaging

INTRODUCTION AND HYPOTHESIS

Defecatory complaints have a severe impact on quality of life. The additional value of pelvic floor MRI in patients with defecatory complaints is unclear. Our aim was to correlate the presence of defects and atrophy of the anal sphincter complex using pelvic floor MRI in women with mixed pelvic floor symptoms and to establish patient characteristics and self reported complaints predictive of pathology.

METHODS

This is a retrospective study among women with mixed pelvic floor symptoms who underwent external phased-array MRI and completed a questionnaire on bothersome defecatory complaints. Data on patient characteristics, including obstetrical history and questionnaire scores were correlated with the assessment of anal sphincter defects and atrophy on pelvic floor MRI.

RESULTS

One hundred and fifty-eight women were included. A defect of the external anal sphincter (EAS) and internal anal sphincter (IAS) was found in 18 (11%) and 5 (3%) patients respectively. Atrophy of the EAS was present in 72 patients (46%), with more cases of mild (n = 52, 33%) than severe atrophy (n = 20, 13%). The variable "previous third or fourth degree tear" had a significant positive association with an IAS defect on MRI, with an OR of 9.533 (1.425-63.776). Patients with EAS atrophy had higher scores for fecal incontinence (indicating more bother) than patients without EAS atrophy. Higher age and BMI were true predictors of the presence of more severe EAS atrophy.

CONCLUSION

Atrophy of the EAS was highly prevalent in this population and was associated with bothersome symptoms of fecal incontinence.

Long-term function and morphology of the anal sphincters and the pelvic floor after primary repair of obstetric anal sphincter injury

AIM

More than 50% of women experience deteriorating continence over time following primary repair of obstetric anal sphincter injuries. The objectives of this study were to assess the function and morphology of the anal sphincters and pelvic floor in women with long-term faecal incontinence after sphincter repair (primary end-point) and to evaluate their correlation with severity of incontinence (secondary end-point).

METHOD

The participants in this prospective study were recruited from a cohort of all women who sustained third or fourth degree obstetric sphincter injury reconstruction (cases) from January 1976 to November 1991. The women who delivered immediately before and after each case, without sustaining obstetric damage, were included as controls. Cases and controls were stratified into three categories: (i) continent; (ii) minor incontinence; and (iii) severe incontinence. The function and morphology of the anal sphincters and pelvic floor were evaluated by MRI, three-dimensional endoanal ultrasonography and anorectal physiology tests.

RESULTS

Fifty-nine women (29 cases/30 controls; mean age 51/53 years; mean follow-up 23.7/24.1 years, respectively) were assessed. Morphologically, cases had a significantly shorter anterior external anal sphincter length compared with controls when evaluated by three-dimensional endoanal ultrasonography (8.6 vs 10.2 mm; P = 0.03). Functionally, cases with severe incontinence had a significantly shorter anterior sphincter length compared with cases with minor incontinence (7.7 vs 10.4 mm; P = 0.04). No correlation could be found between anal pressures and severity of incontinence in the case group.

CONCLUSIONS

Cases had a significantly shorter anterior external anal sphincter length. Functionally, anterior sphincter length correlated with increased severity of incontinence.

Live anatomy of the perineal body in patients with third-degree rectocele

AIM

In many pelvic floor disorders, the perineal body is damaged or destroyed. There is still a considerable variation in anatomical descriptions of the perineal body and even more debate with regard to its attachments and relationships. Cadaveric dissections do not always reflect the functional behaviour of structures in the pelvis and description of live anatomy on imaging studies is not always reliable. This study aimed to define the anatomy of the perineal body in patients with rectocele during the live dissection required for minimally invasive surgical repair.

METHOD

From January 2007 to December 2009 consecutive patients requiring surgery for third-degree rectocele and symptoms of obstructed defaecation were recruited. Participants underwent dissection of the perineal body, rectum and vagina preliminary to a tissue fixation system, an operation which inserts a tensioned tape to repair the perineal body.

RESULTS

Thirty Caucasian female patients, mean age 61 (range 47-87) years, mean parity 2.6 (range 1-5), were included. Live dissection demonstrated that the perineal body was divided into two parts, joined by a stretched central part, anchored laterally by the deep transverse perineii muscle to the descending ramus of the pubic bone. The mean longitudinal length of the perineal body was 4.5 (3.5-5.5) cm, accounting for 50% of the posterior vaginal support.

CONCLUSION

In women with low rectocele, the perineal body appears to be divided into two parts, severely displaced behind the ischial tuberosities.

Perineal body anatomy in living women: 3-dimensional analysis using thin-slice magnetic resonance imaging

OBJECTIVE

The objective of the study was to describe a framework for visualizing the perineal body's complex anatomy using thin-slice magnetic resonance (MR) imaging.

STUDY DESIGN

Two millimeter thick MR images were acquired in 11 women with normal pelvic support and no incontinence/prolapse symptoms. Anatomic structures were analyzed in axial, sagittal, and coronal slices. Three-dimensional (3-D) models were generated from these images.

RESULTS

Three distinct perineal body regions are visible on MR imaging: (1) a superficial region at the level of the vestibular bulb, (2) a midregion at the proximal end of the superficial transverse perineal muscle, and (3) a deep region at the level of the midurethra and puborectalis muscle. Structures are best visualized on axial scans, whereas craniocaudal relationships are appreciated on sagittal scans. The 3-D model further clarifies interrelationships.

CONCLUSION

Advances in MR technology allow visualization of perineal body anatomy in living women and development of 3-D models that enhance our understanding of its 3 different regions: superficial, mid, and deep.

Morphology of the mesorectum in patients with primary rectal cancer

PURPOSE

The size and contents of the pelvis differ between the genders, and this may affect mesorectal size and shape. The aim of this prospective pilot study was to examine radiologically the applied anatomy of the mesorectum.

METHODS

Fifty-eight patients (35 male, 23 female) with primary rectal cancer who had suitable high-resolution staging pelvic magnetic resonance images between November 2002 and July 2004 were studied. Ten variables of mesorectal morphology were measured on axial images at the ischial spines. The associations between morphologic variables and gender and body mass index were examined.

RESULTS

Compared with female patients, male patients had a larger area of overall mesorectal package (3,776 mm2 vs. 2,772 mm2, P = 0.001), larger area of mesorectal fat (2,562 mm2 vs. 1,842 mm2, P = 0.001), and higher ratio of anteroposterior to transverse diameter of the mesorectal package (0.82 vs. 0.56, P < 0.001). The anterior mesorectal fat buffer was significantly thinner in females than in males (2.9 mm vs. 7.8 mm, P < 0.001). Mesorectal fat area was greater in males with a body mass index >25 than with a body mass index <25.

CONCLUSIONS

Males have a larger overall mesorectal package compared with females, mainly caused by mesorectal fat. The anterior mesorectal fat is significantly thinner in females than in males. Such morphologic differences may affect resection margin status.

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.

Malignant rectal obstruction within 5 cm of the anal verge: is there a role for expandable metallic stent placement?

BACKGROUND

Placement of expandable metallic stents (EMS) has been considered contraindicated for patients with malignant rectal obstruction within 5 cm of the anal verge because of the potential problems of anal pain.

OBJECTIVE

Our purpose was to investigate the technical feasibility, clinical effectiveness, and safety of EMS placement in patients with malignant rectal obstruction within 5 cm of the anal verge.

DESIGN

Retrospective study.

SETTING

Single tertiary referral university hospital.

PATIENTS

The sites of obstruction included the rectum within 5 cm (range, 25-50 mm) of the anal verge in 16 patients (group A) and more than 5 cm (range, 53-74 mm) in 14 patients (group B).

INTERVENTIONS

Placement of 3 types of EMS.

MAIN OUTCOME MEASUREMENTS

Complications including pain were evaluated and compared between 2 groups with the Fisher exact test.

RESULTS

The overall technical success rate was 100%. Colon perforation occurred in 2 patients, who underwent emergency surgery. Ten (62.5%) of group A and 1 (7.1%) of group B complained of pain (P = .011). In 3 of the 10 patients in group A, the pain disappeared spontaneously within a week or was tolerated by the patients without use of analgesics, although the remaining 7 patients of group A and the 1 patient in group B needed analgesics until death or elective surgery.

LIMITATIONS

Retrospective study.

CONCLUSIONS

Placement of EMS in patients with malignant rectal obstruction within 5 cm of the anal verge seems feasible and relatively safe and may provide adequate palliation and preoperative decompression of obstruction symptoms. Anal pain was tolerable to the patients with or without use of analgesics.

Three-dimensional transperineal ultrasonography of the pelvic floor: improving visualization for new clinical applications and better functional assessment

OBJECTIVE

With increasing awareness of the scope of pelvic floor disorders has come development and introduction into clinical practice of new imaging techniques, with increasing importance of ultrasonography. Complex pelvic floor anatomy, the conceptual difficulty in the basics of some pelvic floor disorders, and the uneven standardization of ultrasonographic techniques were the impetuses of this review. The purpose of this study was to review the basic anatomy of the pelvic floor and the transperineal ultrasonographic evaluation technique and to provide an overview of the current clinical use of 3-dimensional transperineal ultrasonography in the evaluation of the anterior and posterior pelvic floor compartments.

METHODS

A literature review illustrated with index cases from our center was conducted.

RESULTS

Ultrasonography has been widely applied to evaluation of the anterior and posterior compartments of the pelvic floor. Three-dimensional ultrasonography has a role in improving pelvic floor assessment.

CONCLUSIONS

Three-dimensional transperineal ultrasonography has been applied to evaluation of normal and pathologic pelvic floor anatomy. Practical application, through well-designed and sufficiently powered clinical studies, will establish the association between the clinical presentations of dysfunction with ultrasonographic findings.

Rectourethralis muscle and pitfalls of anterior perineal dissection in abdominoperineal resection and intersphincteric resection for rectal cancer

When performing nerve-sparing abdominoperitoneal resection or intersphincteric resection of lower rectal cancer, difficulty is sometimes encountered during dissection, separation and treatment in the area anterior to the anorectum passing through the levator hiatus between the bilateral levator ani slings owing to missing the surgical plane or venous bleeding. The rectourethralis muscle, which is a mass of smooth muscle, occupies the levator hiatus. The present histological study using nine male cadaveric specimens demonstrated that: (i) the external anal sphincter is likely to be tightly connected to the rectourethralis muscle; (ii) the rectal muscularis propria communicates with the rectourethralis muscle; (iii) the anorectal veins take a tortuous course across the rectourethralis muscle; (iv) Denonvilliers' fascia ends at the rectourethralis muscle; and (v) the rectourethralis muscle provides posterior attachment for the rhabdosphincter. Moreover, the cavernous nerve has been reported to penetrate the rectourethralis muscle. Therefore, careful treatment of the muscle seems to be necessary to avoid male sexual dysfunction. Owing to muscle fiber communications between the rectal muscularis propria and the rectourethralis muscle, and the fact that Denonvilliers' fascia terminates in the rectourethralis muscle, the surgical plane would tend to deeply penetrate the muscle mass. However, mass ligation of the anterior tissues for control of venous bleeding should be avoided. When the tumor is non-anterior, an abdominal surgical plane behind Denonvilliers' fascia is recommended to avoid excess invasion into the rectourethralis muscle.

MRI in evaluating atrophy of the external anal sphincter in patients with fecal incontinence

OBJECTIVE

External anal sphincter atrophy seen at endoanal MRI may predict poor outcome of surgical anal sphincter repair for an external anal sphincter defect. The purposes of this study were to compare external phased-array MRI to endoanal MRI for depicting external anal sphincter atrophy in patients with fecal incontinence and to evaluate observer reproducibility in detecting external anal sphincter atrophy with these techniques.

SUBJECTS AND METHODS

Thirty patients with fecal incontinence (23 women, seven men; mean age, 58.7 years; age range, 37-78 years) underwent both endoanal and external phased-array MRI. Images were evaluated for external anal sphincter atrophy by three radiologists. Measures of differences and agreement between both MRI techniques and of interobserver and intraobserver agreement of both techniques were calculated.

RESULTS

The MRI techniques did not significantly differ in their ability to depict external anal sphincter atrophy (p = 0.63) with good agreement (kappa = 0.72). Interobserver agreement was moderate (kappa = 0.53-0.56) for endoanal MRI and moderate to good (kappa = 0.55-0.8) for external phased-array MRI. Intraobserver agreement was moderate to very good (kappa = 0.57-0.86) for endoanal MRI and fair to very good (kappa = 0.31-0.86) for external phased-array MRI.

CONCLUSION

External phased-array MRI is comparable to endoanal MRI in depicting external anal sphincter atrophy and, thereby, in selecting patients for anal sphincter repair. Because results among interpreters varied considerably depending on the experience level, both techniques can be recommended in the diagnostic workup of fecal incontinence only if sufficient experience is available.

The current role of imaging techniques in faecal incontinence

Faecal incontinence is a common multifactorial disorder. Major causes of faecal incontinence are related to vaginal delivery and prior anorectal surgery. In addition to medical history and physical examination, several anorectal functional tests and imaging techniques can be used to assess the underlying pathophysiology and to guide treatment planning in faecal incontinent patients. Anorectal functional tests provide functional information, but the potential strength comes from combining test results. Imaging techniques, including defecography, endoanal sonography, and magnetic resonance (MR) imaging, provide structural information about the anorectal region with a direct clinical impact. The major role of imaging techniques in faecal incontinence is visualising the structural and functional integrity of the anal sphincter complex. Both two-dimensional endoanal sonography and endoanal MR imaging are accurate tools to depict anal sphincter defects. The major advantage of endoanal MR imaging is the accurate demonstration of external anal sphincter atrophy. Recent studies have suggested that external phased array MR imaging and three-dimensional endoanal sonography are also valuable tools in the diagnostic work up of faecal incontinence. Decisions about the preferred technique will mainly be determined by availability and local expertise. This article demonstrates the current role of tests, predominantly imaging tests, in the diagnostic work up of faecal incontinence.

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

OBJECTIVE

To use magnetic resonance images of living women and 3-dimensional modeling software to identify the component parts and characteristic features of the external anal sphincter (EAS) that have visible separation or varying origins and insertions.

METHODS

Detailed structural analysis of anal sphincter anatomy was performed on 3 pelvic magnetic resonance imaging (MRI) data sets selected for image clarity from ongoing studies involving nulliparous women. The relationships of anal sphincter structures seen in axial, sagittal, and coronal planes were examined using the 3-D Slicer 2.1b1 software program. The following were requirements for sphincter elements to be considered separate: 1) a clear and consistently visible separation or 2) a different origin or insertion. The characteristic features identified in this way were then evaluated in images from an additional 50 nulliparas for the frequency of feature visibility.

RESULTS

There were 3 components of the EAS that met criteria as being "separate" structures. The main body (EAS-M) is separated from the subcutaneous external anal sphincter (SQ-EAS) by a clear division that could be observed in all (100%) of the MRI scans reviewed. The wing-shaped end (EAS-W) has fibers that do not cross the midline ventrally, but have lateral origins near the ischiopubic ramus. This EAS-W component was visible in 76% of the nulliparas reviewed.

CONCLUSION

Three distinct external anal sphincter components can be identified by MRI in the majority of nulliparous women.

Anal sphincter defects in patients with fecal incontinence: endoanal versus external phased-array MR imaging

PURPOSE

To prospectively compare external phased-array magnetic resonance (MR) imaging with endoanal MR imaging in depicting external and internal anal sphincter defects in patients with fecal incontinence and to prospectively evaluate observer reproducibility in the detection of external and internal anal sphincter defects with both MR imaging techniques.

MATERIALS AND METHODS

The medical ethics committees of both participating hospitals approved the study, and informed consent was obtained. Thirty patients (23 women, seven men; mean age, 58.7 years; range, 37-78 years) with fecal incontinence underwent MR imaging with both endoanal and external phased-array coils. MR images were evaluated by three radiologists with different levels of experience for external and internal anal sphincter defects. Measures of inter- and intraobserver agreement of both MR imaging techniques and of differences between both imaging techniques were calculated.

RESULTS

Both MR imaging techniques did not significantly differ in the depiction of external (P > .99) and internal (P > .99) anal sphincter defects. The techniques corresponded in 25 (83%) of 30 patients for the depiction of external anal sphincter defects and in 28 (93%) of 30 patients for the depiction of internal anal sphincter defects. Interobserver agreement was moderate to good for endoanal MR imaging and poor to fair for external phased-array MR imaging. Intraobserver agreement ranged from fair to very good for both imaging techniques.

CONCLUSION

External phased-array MR imaging is comparable to endoanal MR imaging in the depiction of clinically relevant anal sphincter defects. Because of the weak interobserver agreement, both MR imaging techniques can be recommended in the diagnostic work-up of fecal incontinence only if sufficient experience is available.

Sexually dimorphic micturition in rats: relationship of perineal muscle activity to voiding pattern

In the present study we examined the possibility that striated muscle activity may underlie sexually dimorphic micturition in rats. Micturition dynamics, the gross anatomy of the external urethral sphincter, and the participation of the striated perineal muscles in micturition were compared in urethane-anesthetized adult male and female rats. Bladder contraction characteristics, particularly the magnitude of bladder high-frequency pressure waves during voiding, differed between sexes. Dissections indicated that the sphincter was more extensive and thicker in males than in females. Electromyography showed that in both sexes the sphincter discharged in bursts that correlated with the rising phase of high-frequency bladder pressure oscillations. Regional differences in discharge pattern were seen in the sphincters of males, with the proximal part of the sphincter showing components activated during bladder filling. Bulbospongiosus, ischiocavernosus, and cremaster muscles also were activated during bladder contraction in males. In both sexes transection of the motor branch of the lumbosacral plexus eliminated the bladder high-frequency oscillations and reduced voided volume. Neurectomy did not affect bladder pressure but reduced voiding efficiency by 45% in males. In females the bladder pressure was dramatically decreased, but voiding efficiency only decreased by 24%. Our findings suggest that, in rats, striated perineal muscles contribute to the sexually dimorphic micturition. Activity of the dimorphic perineal muscles may regulate genital and urinary urethra expulsive functions, helping to expel seminal plug and fluids through the long urethra in the male.

Magnetic resonance imaging anatomy of the anal canal

The anatomy of the anal canal is complex but well demonstrated by MRI. Understanding the anatomy is a prerequisite for determining the true site and the extent of pathology, especially for surgical workup. In this article, the MRI anatomy of the anal canal has been displayed using highlighted MRI images and line diagrams.

Faecal incontinence in adults

Faecal incontinence can affect individuals of all ages and in many cases greatly impairs quality of life, but incontinent patients should not accept their debility as either inevitable or untreatable. Education of the general public and of health-care providers alike is important, because most cases are readily treatable. Many cases of mild incontinence respond to simple medical therapy, whereas patients with more advanced incontinence are best cared for after complete physiological assessment. Recent advances in therapy have led to promising results, even for patients with refractory incontinence. Health-care providers must make every effort to communicate fully with incontinent patients and to help restore their self-esteem, eliminate their self-imposed isolation, and allow them to resume an active and productive lifestyle.

Differentiation of Anal Sphincters With High-Resolution Magnetic Resonance Imaging Using Contrast-Enhanced Fast Low-Angle Shot 3-Dimensional Sequences

OBJECTIVE

The imaging of the anal apparatus is becoming more and more important in the management of patients who suffer from anorectal disease. The exact differentiation of the sphincter muscles is a major requirement for the detection of disorders of the anal canal. The purpose of this study was to evaluate a new magnetic resonance (MR) imaging protocol using contrast-enhanced, high-resolution, fast low-angle shot, 3-dimensional (3D) sequences and image subtraction regarding the visualization and differentiation of the internal and external sphincter muscles.

METHODS

High-resolution pelvic MR imaging (1.5 T) was performed in 85 patients (42 male, 43 female; age range: 12-81 years) with a phased-array body coil. For an anatomic overview of the pelvic region, a short tau inversion recovery sequence in the coronal plane was carried out, followed by a 3D, high-resolution, fat-saturated, T1-weighted, gradient echo sequence before and after intravenous administration of a contrast agent (gadobenic acid, 0.15 mmol/kg). To optimize the visualization of the sphincter muscles, subtraction of the unenhanced from the contrast-enhanced sequences was routinely performed. The signal intensities of the internal and external sphincter muscles were measured in the axial plane on the subtracted images.

RESULTS

The distribution of the mean signal intensities of the internal and external sphincter muscles as well as the difference between both revealed a normal deviation. The confidence interval on a 95% significance level ranged between 1.6941 and 1.9393, with a mean of 1.81. In the whole study group, the signal intensity of the internal sphincter muscle was significantly higher than that of the external sphincter, thus facilitating the identification and differentiation of the 2 components of the anal sphincter complex.

CONCLUSION

The presented MR imaging protocol is robust, provides a high image quality, and is well accepted by patients because of its noninvasiveness.

Detection and characterization of perianal inflammatory disease: accuracy of transperineal combined gray scale and color Doppler sonography

OBJECTIVE

To evaluate the accuracy of transperineal gray scale and color Doppler sonography for the detection and characterization of perianal inflammatory disease with surgical correlation.

METHODS

Eighty-seven patients with suspected perianal inflammatory disorders underwent transperineal gray scale and color Doppler sonography with a linear 4- to 7-MHz transducer that was used to scan the entire perianal region for the detection of suspected inflammatory disorders. Each detected inflammatory disorder was evaluated to determine its morphologic characteristics and extent. Color Doppler sonography was applied to assess the presence of increased vascularity in the perianal region. In comparison with surgical findings, the diagnostic performance of transperineal sonography was assessed by means of receiver operating characteristic analysis for lesion detection and the Spearman rho test for lesion characterization. Logistic regression analysis was used to assess whether increased perineal vascularity was a predictive factor of perianal inflammatory disease.

RESULTS

Seventy-seven perianal inflammatory disorders were confirmed in 62 patients. Gray scale sonography achieved a significantly good performance in the detection (area under the curve = 0.86; P < .001) and characterization (r = 0.65; P < .001) of perianal inflammatory disease. For the detection of perianal fistulas and abscesses, sensitivity was 100% for both, and specificity was 100% and 94%, respectively. With the use of color Doppler sonography, the diagnostic confidence increased slightly (area under the curve = 0.89) but significantly (P = .002). Logistic regression analysis identified hypervascularity at the periphery of a perianal lesion as a significant independent predictor of an inflammatory disease.

CONCLUSIONS

Combined gray scale and color Doppler sonography enables a high detectability rate and comprehensive characterization of perianal abscesses and fistulas.

Potential clinical implications of direction of a trans-sphincteric anal fistula track

Background

The longitudinal direction of a trans-sphincteric anal fistula track through the anal sphincter complex may have implications regarding fistulotomy.

Methods

The angle of the track of trans-sphincteric fistulas relative to the longitudinal axis of the anal canal was measured before operation by means of magnetic resonance imaging (MRI) in 46 patients. This was compared with the findings at operation.

Results

The track passed cranially as well as laterally at an acute angle (less than 90°) in 23 patients while it passed either transversely or caudally at an obtuse angle (90° or more) in the remaining 23. The internal opening was significantly higher in relation to the dentate line (above in eight patients, at the dentate line in 14 and below in one patient) when the track was acute than when it was obtuse (above in one, at the dentate line in 17 and below in five patients) (P = 0·004). The fistula track crossed the sphincter at a median angle of 35°, 95° and 132° from internal openings sited above, at and below dentate line level respectively (P = 0·002).

Conclusion

Fistula tracks passed cranially and laterally through the sphincter complex in half of these patients, and were most acutely angled on MRI when internal openings were situated above the dentate line. Preoperative MRI might alert surgeons to the potential hazard of fistulotomy being more extensive than anticipated from simple palpation of the level of the internal opening.