External anal sphincter defects in patients with fecal incontinence: comparison of endoanal MR imaging and endoanal US

PURPOSE: To prospectively compare in a multicenter study the agreement between endoanal magnetic resonance (MR) imaging and endoanal ultrasonography (US) in depicting external anal sphincter (EAS) defects in patients with fecal incontinence. MATERIALS AND METHODS: The study was approved by the medical ethics committee of all participating centers. A total of 237 consenting patients (214 women, 23 men; mean age, 58.6 years +/- 13 [standard deviation]) with fecal incontinence were examined from 13 different hospitals by using endoanal MR imaging and endoanal US. Patients with an anterior EAS defect depicted on endoanal MR images and/or endoanal US scans underwent anal sphincter repair. Surgical findings were used as the reference standard in the determination of anterior EAS defects. The Cohen kappa statistic and McNemar test were used to calculate agreement and differences between diagnostic techniques. RESULTS: Agreement between endoanal MR imaging and endoanal US was fair for the depiction of sphincter defects (kappa = 0.24 [95% confidence interval: 0.12, 0.36]). At surgery, EAS defects were found in 31 (86%) of 36 patients. There was no significant difference between MR imaging and US in the depiction of sphincter defects (P = .23). Sensitivity and positive predictive value were 81% and 89%, respectively, for endoanal MR imaging and 90% and 85%, respectively, for endoanal US. CONCLUSION: In the selection of patients for anal sphincter repair, both endoanal MR imaging and endoanal US are sensitive tools for preoperative assessment, and both techniques can be used to depict surgically repairable anterior EAS defects.     

Prospective assessment of accuracy of endoanal MR imaging and endosonography in patients with fecal incontinence

OBJECTIVE: Endoanal MR imaging was prospectively compared with anal endosonography to determine any superiority in the characterization of sphincter morphology in fecal incontinence. SUBJECTS AND METHODS: Fifty-two consecutive patients with fecal incontinence were examined with anal endosonography and endoanal MR imaging after a detailed bowel history, clinical examination, and complete anorectal physiologic testing. External and internal anal sphincter integrity was noted on both endosonograms and MR images by two radiologists in consensus, who read individual scans in a random order to avoid recall bias. Imaging findings were subsequently compared, and arbitration of any disagreement between endosonography and MR imaging was made in consensus by a surgeon and a gastroenterologist who also had access to the patient's history, clinical examination, and anorectal physiologic testing results. RESULTS: Complete agreement was found between anal endosonographic and MR imaging interpretations in 32 patients (62%): 10 with combined external and internal sphincter injuries, two with isolated internal sphincter injury, and 20 with intact sphincters. Of 20 patients in whom results of the scans were disparate, incorrect interpretation was found on endosonography in six patients, on MR imaging in 15. Overall, one error relating to the internal sphincter was made on endosonography versus 12 on MR imaging (p = 0.002), and five errors relating to the external sphincter were made on endosonography versus six on MR imaging (p = 1.0). CONCLUSION: This study suggests that endoanal sonography and endoanal MR imaging are equivalent in diagnosing external anal sphincter injury, but MR imaging is inferior in diagnosing internal anal sphincter injury.     

Measurement of anal sphincter muscles: endoanal US, endoanal MR imaging, or phased-array MR imaging? A study with healthy volunteers.

PURPOSE: To compare endoanal ultrasonography (US), endoanal magnetic resonance (MR) imaging, and phased-array MR imaging for anal sphincter muscle measurement. MATERIALS AND METHODS: Sixty healthy volunteers underwent 1.5-T phased-array MR, endoanal MR, and endoanal US examinations. Sphincter muscle thicknesses were measured. Measurement reliability was analyzed, and correlations among the imaging methods were calculated. Multivariate analysis was performed to assess the influence of age, weight, height, sex, parity, and obstetric trauma on sphincter dimensions. RESULTS: Both MR methods had good reliability for measurements of all sphincter components, whereas endoanal US was reliable for internal sphincter measurement only. There was little correlation between the techniques, except between the two MR techniques, with a strong correlation for total sphincter and perineal body thickness. The internal sphincter thickened significantly (P =.002) with age at endoanal US and endoanal MR imaging but not at phased-array MR imaging. There were small sex-based differences in sphincter muscle measurements at phased-array MR imaging only. CONCLUSION: Endoanal US enables reliable measurement of only internal sphincter thickness, whereas both MR imaging methods enable reliable measurement of all sphincter components. Sphincter measurement with phased-array MR imaging is as reliable as that with endoanal MR imaging.     

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.     

High-resolution magnetic resonance imaging of the anal sphincter using a dedicated endoanal receiver coil

The use of a surface coil in MR imaging improves signal-to-noise ratio of adjacent tissues of interest. We therefore devised an endoanal receiver coil for imaging the anal sphincter. The probe is solid and re-usable: it comprises a saddle geometry receiver with integral tuning, matching and decoupling. It is placed in the anal canal and immobilised externally. Both in vitro and in vivo normal anatomy is identified. The mucosa is high signal intensity, the submucosa low signal intensity, the internal sphincter uniformly high signal intensity and the external sphincter low signal intensity on T1- and T2-weighted images. In females, the transverse perineal muscle bridges the inferior part of the external sphincter anteriorly. In perianal sepsis, collections and the site of the endoanal opening are identified. In early-onset fecal incontinence following obstetric trauma/surgery, focal sphincter defects are demonstrated; in late-onset fecal incontinence external sphincter atrophy is seen. In fecally incontinent patients with scleroderma, forward deviation of the anterior sphincter musculature with descent of rectal air and feces into the anal canal is noted. The extent of sphincter invasion is assessed in low rectal tumours. In children with congenital anorectal anomalies, abnormalities of the muscle components are defined using smaller-diameter coils. Such information is invaluable in the assessment and surgical planning of patients with a variety of anorectal pathologies. Received: 17 March 1998; Revision received: 19 May 1998; Accepted: 27 May 1998     

Anal incontinence: diagnosis by endoanal US or endovaginal MRI

Preoperative evaluation was made of the diagnostic value of endoanal ultrasound (EAUS) and endovaginal magnetic resonance imaging (EVMRI) in diagnosing anal sphincter defects as the cause of anal incontinence. Nineteen female individuals with anal incontinence were examined clinically with EAUS and with EVMRI at 1.5 T using a prostatic coil. The findings were evaluated independently and compared with findings at surgery. In diagnosing external anal sphincter defects, EAUS and EVMRI showed almost similar agreement with surgical findings, 12 (63%) out of 19 vs 11 (58%), respectively. Internal anal sphincter defects were equally detected by EAUS and EVMRI as compared with surgical diagnosis. There was considerable variation between radiologists in diagnosing defects by EVMRI. EAUS and EVMRI are equal in diagnosing anal sphincter defects.Abbreviations IAS Internal anal sphincter - EAS External anal sphincter - EAUS Endoanal ultrasound - MR Magnetic resonance - PPV Positive predictive value - NPV Negative predictive value - EVMRI Endovaginal magnetic resonance imaging - EAMRI Endoanal magnetic resonance imaging     

Endoanale Magnetresonanztomographie bei fäkaler Inkontinenz

PURPOSE: Within the recent years several studies have been performed to determine the value of endoanal magnetic resonance imaging (MRI) in faecal incontinence. METHODS: MRI is performed using a 0.5-1.5 T unit. A surface coil with a maximum diameter of 19 mm is placed in the anal canal. T2* 3D gradient-echo-sequences and T2-weighted turbo-spin-echo sequences in coronal, axial und sagittal orientation are acquired. RESULTS: Compared to endoanal ultrasound (EUS), which is the gold standard for diagnosis in faecal incontinence, endoanal MRI is better in visualization of the external sphincter. The accurate delineation of the external sphincter has led to the possibility to evaluate sphincter atrophy. Preliminary results have shown, that endoanal MRI has an accuracy of 90-95% in the demonstration of lesions in the external sphincter. In detection of lesions of the internal sphincter EUS is still superior to endoanal MRI. CONCLUSION: EUS and endoanal MRI are currently the optimal imaging techniques for faecal incontinence, with the advantage of detecting external sphincter atrophy with endoanal MRI.     

Magnetic Resonance Imaging of the anal canal using high resolution sequences and phased array coil: visualization of anal sphincter complex

PURPOSE: To assess the normal anatomy of the anal sphincter complex using high-resolution MR imaging with phased -array coil. MATERIAL AND METHODS: Twenty patients, 13 males and 7 females, ranging in age between 27 and 56 years underwent MRI evaluation of the pelvic region, using a superconductive 1.5 T magnet (maximum gradient strength, 25 mT/m; minimum rise time 600 microseconds, equipped with phased-array coil. High-resolution T2-weighted Turbo Spin Echo sequences (TR, 4055 ms; TE, 132 ms; matrix 390x512; in-plane resolution, 0.67x0.57 mm) were acquired on multiple axial, sagittal and coronal planes. Images were reviewed by two experienced gastrointestinal radiologists in order to evaluate the normal anal sphincter complex. RESULTS: Optimal image quality of the anal sphincter complex was obtained in all cases. Different muscular layers were observed between the upper and lower aspects of the anal canal. In the lower part of the anal canal, internal and external sphincter muscles could be observed; in the upper part, puborectal and internal sphincter muscles were depicted. Good visualization of intersphincteric space, levator ani muscle and ischioanal space was also obtained in all cases. CONCLUSIONS: High-resolution MR images with phased-array coil provide optimal depiction of the anal canal and the anal sphincter complex.     

Transvaginal sonography of the anal sphincter: reliable, or not?

OBJECTIVE: The purpose of this study was to validate the use of transvaginal sonography for anal sphincter evaluation, compare this technique with the more commonly used transanal technique, and explain a publication that suggested that transvaginal sonography is unreliable. SUBJECTS AND METHODS: The study population consisted of 50 women, of whom 44 prospectively underwent transanal and transvaginal sonography. The six remaining patients with surgical confirmation underwent only transvaginal sonography. All images were interpreted by the examining radiologist and then reviewed by a second radiologist who was unaware of the first radiologist's interpretations. Defects in the external and internal anal sphincters, the status of the perineal body, and any perianal collections or fistulas were documented. RESULTS: Twenty-five of the 50 patients showed sphincteric defects. Twenty-two had a defect in the external anal sphincter, of whom 16 had a matching internal anal sphincter defect. Four patients had an isolated internal anal sphincter defect. Surgery in nine of these 22 patients confirmed the defects seen on sonography. The 10th patient who underwent surgery had scar tissue rather than a tear in the external anal sphincter that corresponded with the defect seen on sonography. Defects were identified in all patients presenting with fecal incontinence who had undergone either a primary repair or an anterior sphincteroplasty. Of the 25 patients with intact sphincters on both transvaginal and transanal sonography, four had other significant findings including two perianal abscesses and two T3 rectal carcinomas. In 40 of the 44 patients who were prospectively imaged using both techniques, the sonographic findings were in agreement. Review, performed by a second radiologist who was unaware of the first radiologist's interpretations, verified the findings resulting in an 88.6% interobserver agreement. In all patients, perineal body assessment and assessment of perianal inflammatory disease was more accurate with the transvaginal technique. CONCLUSION: Transvaginal sonography is a reliable method for evaluating the anal sphincter, with an accuracy equivalent to that of the transanal technique. Transvaginal sonography is preferable for evaluation of the perineal body and perianal inflammatory processes.     

Imaging of the anorectal region

Imaging of anorectal region has drastically changed during the last decade. Transrectal ultrasound and transrectal MRI can be used for staging the rectal tumours. Endoanal sonography can be applied for the classification of perianal fistulae and identification of anal sphincter defects in patients with faecal incontinence. Due to the limitations of endoanal sonography, endoanal MRI was introduced to assess the pathology related to the anal sphincter complex. Endoanal MRI seems superior to endoanal sonography. This paper describes the new developments of the imaging techniques and presents new insights in anatomy and pathology of the anorectum.     

Imaging of the posterior pelvic floor

Disorders of the posterior pelvic floor are relatively common. The role of imaging in this field is increasing, especially in constipation, prolapse and anal incontinence, and currently imaging is an integral part of the investigation of these pelvic floor disorders. Evacuation proctography provides both structural and functional information for rectal voiding and prolapse. Dynamic MRI may be a valuable alternative as the pelvic floor muscles are visualised, and it is currently under evaluation. Endoluminal imaging is important in the management of anal incontinence. Both endosonography and endoanal MRI can be used for detection of anal sphincter defects. Endoanal MRI has the advantage of simultaneously evaluating external sphincter atrophy, which is an important predictive factor for the outcome of sphincter repair. Many aspects of constipation and prolapse remain incompletely understood and treatment is partly empirical; however, imaging has a central role in management to place patients into treatment-defined groups.     

Endoluminal MR imaging of anorectal diseases.

Endoluminal magnetic resonance imaging (MRI) has become an important technique in the diagnostic work-up of patients with anorectal diseases. The high spatial resolution of endoluminal MRI gives a detailed demonstration of the anal and rectal anatomy and pathology. This technique has been demonstrated to be superior to endoluminal sonography and body coil MRI. Endoanal MRI and phased-array coil MRI seem to have comparable results in perianal fistulas, but comparative data are lacking. Phased-array coil MRI is the imaging technique of choice for imaging rectal tumors, while endoluminal MRI is the alternative technique for imaging rectal tumors and the preferred technique for imaging anal tumors. Endoluminal MRI is superior to phased-array coil MRI in fecal incontinence, as phased-array coil MRI does not give the detailed spatial resolution required for evaluation of anal sphincter lesions.     

Endoluminal MR imaging of the rectum and anus: technique, applications, and pitfalls.

Anorectal diseases (e.g., fecal incontinence, perianal and anovaginal fistulas, anorectal tumors) require imaging for proper case management. Endoluminal magnetic resonance (MR) imaging has become an important part of diagnostic work-up in such cases. Optimal endoluminal MR imaging requires careful attention to patient preparation, imaging protocols, and potential pitfalls in interpretation. Comfortable positioning and the use of an antiperistaltic drug are vital for adequate patient preparation. Selected sequences and imaging planes are used in imaging protocols tailored for specific diseases. In fecal incontinence, three-dimensional sequences allow detailed demonstration of the anal anatomy and related defects. In perianal and anovaginal fistulas, longitudinal imaging planes help determine the superior extent of the abnormality. In anorectal tumors, T1-weighted turbo spin-echo MR imaging can help detect extension into the perirectal fat and T2-weighted turbo spin-echo MR imaging is used to optimize contrast between tumor and the rectal wall. Off-axis and radial imaging planes are used in all anorectal diseases to minimize partial volume effects. Potential pitfalls include various parts of the normal anal anatomy mimicking sphincter defects, veins and hemorrhoids mimicking fistulas and abscesses, and overhanging tumor mimicking more extensive tumor. Adequate patient preparation combined with proper technique and a knowledge of potential pitfalls will allow optimal endoluminal MR imaging of the rectum and anus.     

Pelvic floor muscle lesions at endoanal MR imaging in female patients with faecal incontinence

To evaluate the frequency and spectrum of lesions of different pelvic floor muscles at endoanal MRI in women with severe faecal incontinence and to study their relation with incontinence severity and manometric findings. In 105 women MRI examinations were evaluated for internal anal sphincter (IAS), external anal sphincter (EAS), puborectal muscle (PM) and levator ani (LA) lesions. The relative contribution of lesions to differences in incontinence severity and manometric findings was studied. IAS (n = 59) and EAS (n = 61) defects were more common than PM (n = 23) and LA (n = 26) defects. PM and LA defects presented mainly with IAS and/or EAS defects (isolated n = 2 and n = 3). EAS atrophy (n = 73) was more common than IAS (n = 19), PM (n = 16) and LA (n = 9) atrophy and presented mainly isolated. PM and LA atrophy presented primarily with EAS atrophy (isolated n = 3 and n = 1). Patients with IAS and EAS lesions had a lower resting and squeeze pressure, respectively; no other associations were found. PM and LA lesions are relatively common in patients with severe faecal incontinence, but the majority of lesions are found in women who also have IAS and/or EAS lesions. Only an association between anal sphincter lesions and manometry was observed.     

Endoanal ultrasound evaluation of anorectal diseases and disorders: technique, indications, results and limitations

Imaging of the rectum, anorectal junction and surrounding tissues is both difficult and technically challenging. CT and conventional barium studies offer limited information in local staging of rectal and perirectal neoplasms, anal carcinomas and extension perianal fistulas in patients with inflamamatory bowel disease, or in evaluating patients with fecal incontinence. During past decade, sonography and MR imaging have resulted in significant improvement in the imaging of rectal and perirectal and anal and perianal disease. The aim of this article is to review possibility of the EAUS in the evaluation both normal anal anatomy and anorectal disease and disorders (anal carcinoma, sphincter defects, anal fistulas, perianal abscesses and other pathological conditions).     

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.     

Congenital anorectal atresia: MR imaging of late post-operative appearances in adult patients with anal incontinence

Objectives

To describe the MR imaging findings in adults presenting with anal incontinence following pull-through perineoplasty for anorectal atresia.

Methods

15 adults (12 male, 3 female; age 22–52 years) with anal incontinence following a prior perineal pull-through procedure as an infant for anorectal atresia were identified retrospectively. MR imaging was performed using either an endoanal coil or body coil. MR images were reviewed by three observers who noted whether pelvic floor and sphincter muscles were present and, if so, whether they were thinned or not. Data were tabulated and raw frequencies determined.

Results

Images were unavailable for one patient, leaving 14 for analysis. Anal stenosis prevented endoanal coil placement in 5. The pull-through was anatomically correct in 12 (86 %) patients but was misdirected in 2. Thinned muscle was seen in 11 (79 %) patients. External sphincter thinning was commonest (present in 10 patients), with levator plate thinning least common (present in 4 patients). Only one patient had thinning of all muscle groups.

Conclusion

MR imaging may be used to determine the extent and quality of residual pelvic floor and anal sphincter muscle in adults who have functional disability following pull-through perineoplasty for anorectal agenesis.

Key Points:

? MR imaging can delineate the extent of residual muscle following perineoplasty. ? Endoanal MR, where possible, provides optimal information regarding residual muscle. ? MR imaging is useful to guide therapy for patients who are anally incontinent as adults.     

Comparison of transanal and external perineal ultrasonography

Anal endosonography with rotating endoprobes provides state-of-the-art imaging of sphincter integrity; however, the technique is not widely available and requires expensive equipment. Since pelvic anatomy permits the use of standard external ultrasound probes, we tested the feasibility, tolerance and reproducibility of uniplanar perineal sonography, with respect to visualisation of the anal sphincter, using both convex and linear 3.5- to 7.5-MHz and 360 degree rotating 7-MHz probes. Twenty healthy nulliparus female volunteers were investigated. Two operators performed endosonography and perineal sonography in duplicate, each blinded to the findings of the other. We then used this technique to examine 20 postpartum primiparus patients. The examination was well tolerated by all subjects. The internal anal sphincter appeared in perineal sonography as a hypoechogenic ring surrounded by an echogenic ring representing the external anal sphincter. Endosonography revealed six sphincter tears, four external and internal sphincter tears, one isolated external tear and one isolated internal tear. Perineal sonography recognised in all cases external sphincter tears. In one case the internal sphincter defect was missed. Perineal sonography appears to be a feasible alternative to anal endosonography in female patients and provides good information on external sphincter defects suggesting that this procedure might be particularly useful in incontinence screening. Perineal sonography gives a good image of internal sphincter. The lack of an isolated internal defect cannot be considered as relevant to our study.     

Female anal sphincter: age-related differences in asymptomatic volunteers with high-frequency endoanal US

PURPOSE: To evaluate endoanal ultrasonographic (US) anatomy in a large group of nulliparous women by using a high-frequency 10-MHz transducer to define normal age-related differences in sphincter morphology. MATERIALS AND METHODS: One hundred fifty asymptomatic nulliparous women (mean age, 31 years; range, 19-80 years) underwent endoanal US with a high-frequency 10-MHz transducer. Anal canal structures were measured at high, middle, and low levels and were correlated with age by using the Pearson simple linear correlation coefficient. RESULTS: Internal sphincter thickness showed a highly significant positive correlation with age at both sites at which it was measured (high anal canal, r = 0.34, P <.001; middle anal canal, r = 0.33, P <.001). External sphincter thickness showed a highly significant negative correlation with age at all sites measured (high anal canal, r = -0.65, P <.001; middle anal canal, r = -0.49, P <.001; low anal canal, r = -0.21, P =.012). There was no significant correlation between age and thickness of subepithelial tissue, longitudinal muscle, or puborectalis muscle. Subjects whose internal sphincter showed mixed echogenicity were significantly older than those whose internal sphincter was uniformly hypoechoic (mean, 47.4 vs 34.6 years; P <.001). Subjects with mixed internal sphincter echogenicity also had a significantly thinner external sphincter at high (mean thickness, 3.8 vs 4.6 mm; P <.001) and middle (mean thickness, 3.7 vs 4.1 mm; P =.03) anal canal levels. CONCLUSION: At older ages there are increased internal anal sphincter thickness and decreased external anal sphincter thickness. Diagnosis of external sphincter atrophy on the basis of sphincter thinning requires that one distinguish between abnormal thinning and age-related differences.