Endoanal coil in MR imaging of anal fistulas

The treatment of anal fistula: second ACPGBI Position Statement - 2018

It is over 10 years since the first ACPGBI Position Statement on the management of anal fistula was published in 2007. This second edition is the result of scrutiny of the literature published during this time; it updates the original Position Statement and reviews the published evidence surrounding treatments for anal fistula that have been developed since the original publication.

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.

A global consensus on the classification, diagnosis and multidisciplinary treatment of perianal fistulising Crohn's disease

OBJECTIVE

To develop a consensus on the classification, diagnosis and multidisciplinary treatment of perianal fistulising Crohn's disease (pCD), based on best available evidence.

METHODS

Based on a systematic literature review, statements were formed, discussed and approved in multiple rounds by the 20 working group participants. Consensus was defined as at least 80% agreement among voters. Evidence was assessed using the modified GRADE (Grading of Recommendations Assessment, Development, and Evaluation) criteria.

RESULTS

Highest diagnostic accuracy can only be established if a combination of modalities is used. Drainage of sepsis is always first line therapy before initiating immunosuppressive treatment. Mucosal healing is the goal in the presence of proctitis. Whereas antibiotics and thiopurines have a role as adjunctive treatments in pCD, anti-tumour necrosis factor (anti-TNF) is the current gold standard. The efficacy of infliximab is best documented although adalimumab and certolizumab pegol are moderately effective. Oral tacrolimus could be used in patients failing anti-TNF therapy. Definite surgical repair is only of consideration in the absence of luminal inflammation.

CONCLUSIONS

Based on a multidisciplinary approach, items relevant for fistula management were identified and algorithms on diagnosis and treatment of pCD were developed.

Improving the outcome of fistulising Crohn's disease

Fistulas are a frequent manifestation of Crohn's disease (CD) and can result in considerable morbidity. Approximately 35% of all patients with CD will experience one fistula episode during their disease course of which 54% is perianal. The major symptoms of patients with perianal fistulas are constant anal pain, the formation of painful swellings around the anus and continuous discharge of pus and/or blood from the external fistula opening. The exact aetiology of perianal fistulas in CD patients remains unclear, but it is thought that a penetrating ulcer in the rectal mucosa caused by active CD forms an abnormal passage between the epithelial lining of the rectum and the perianal skin. Genetic, microbiological and immunological factors seem to play important roles in this process. Although the incidence of perianal fistulas in patients with CD is quite high, an effective treatment is not yet discovered. In this review all available medical and surgical therapies are discussed and new treatment options and research targets will be highlighted.

MRI in evaluation of perianal fistula

This essay illustrates the usefulness of MRI in evaluating perianal fistulas, a common disease, notorious for recurrence if not assessed and treated adequately. MRI exquisitely depicts the perianal anatomy and shows the fistulous tracks and their associated ramifications and abscesses. It thus provides an excellent preoperative understanding of the disease, enabling selection of the most appropriate surgical treatment and therefore minimising all chances of recurrence.

Idiopathic fistula-in-ano

Fistula-in-ano is the most common form of perineal sepsis. Typically, a fistula includes an internal opening, a track, and an external opening. The external opening might acutely appear following infection and/or an abscess, or more insiduously in a chronic manner. Management includes control of infection, assessment of the fistulous track in relation to the anal sphincter muscle, and finally, definitive treatment of the fistula. Fistulotomy was the most commonly used mode of management, but concerns about post-fistulotomy incontinence prompted the use of sphincter preserving techniques such as advancement flaps, fibrin glue, collagen fistula plug, ligation of the intersphincteric fistula track, and stem cells. Many descriptive and comparative studies have evaluated these different techniques with variable outcomes. The lack of consistent results, level I evidence, or long-term follow-up, as well as the heterogeneity of fistula pathology has prevented a definitive treatment algorithm. This article will review the most commonly available modalities and techniques for managing idiopathic fistula-in-ano.

Current techniques in imaging of fistula in ano: three-dimensional endoanal ultrasound and magnetic resonance imaging

Perianal fistula is an abnormal communication between the anal canal and perianal skin. The majority of perianal fistulous disease results from either cryptoglandular inflammation or Crohn's disease. These groups differ in pathophysiology, prognosis, and strategies for imaging and treatment. Endoanal ultrasound and magnetic resonance imaging represent current imaging strategies for evaluating perianal fistulas and may be used alone or in combination. The use of three-dimensional technique and peroxide fistulography optimize the ultrasound evaluation of perianal fistula. The use of multiple imaging planes and sequences including fat suppression and contrast enhancement optimize the magnetic resonance imaging protocol. Examples of the imaging appearance of perianal fistulas and a proposed flowchart for imaging modality selection are provided.

Simple clinical examination predicts complexity of perianal fistula

OBJECTIVE

To investigate the diagnostic value of the distance between external opening of perianal fistula and anal verge and to evaluate its relation to the type of fistula. Preoperative identification of complex fistulae is important for proper planning of treatment.

PATIENTS AND METHODS

One hundred and fifteen consecutive patients operated for perianal fistula were studied prospectively. The distance between the external opening and the anal verge was measured. Location of the external opening, demographic and medical history data were correlated with characteristics of the fistulae. Data analysis was performed using the SPSS statistical package. The association between categorical variables was examined using the chi(2)-test or Fisher's exact test for small sample. Comparison of continuous variables between two groups was analysed by t-test.

RESULTS

The mean distance between external opening and anal verge in simple fistulae was 2.8 cm (range 1.5-4.3, SD 0.689) and in complex fistulae it was 4.4 cm (range 3.5-6.0, SD 0.526). This difference was statistically significant -P < 0.0001. Age and previous operations (particularly attempted definitive operations) were also significantly related to the complexity of the fistula. Data concerning location and direction of the fistulous tracts confirm the validity of Goodsall's rule.

CONCLUSION

Simple preoperative clinical examination may reliably predict the complexity of a perianal fistula. Identification of these patients permits to select the cases that should have specific sophisticated preoperative work-up. The first definitive operation is most important to assure a successful outcome, thus such preoperative triage may also permit selective referral to a specialized colorectal team.

Imaging of fistula in ano

Fistula in ano is a common condition that often recurs despite seemingly adequate surgery, usually because of infection that was missed at surgery. It is now increasingly recognized that preoperative imaging can help identify infection that would have otherwise gone unidentified. In particular, magnetic resonance (MR) imaging findings have been shown to influence surgery and markedly diminish the chance of recurrence; thus, preoperative imaging will become increasingly routine in the future. In this article, the authors describe the pathogenesis, classification, and imaging of fistula in ano, with an emphasis on MR imaging. Most important, the authors describe how the radiologist is well placed to answer the surgical riddles that must be solved for treatment to be effective.

Diagnostic accuracy of body coil MRI in describing the characteristics of perianal fistulas

OBJECTIVE

The purpose of this study was to determine the accuracy of synergic body coil MRI using SPIR technique without contrast, in the determination of fistula characteristics in patients with clinically positive signs.

METHOD AND SUBJECTS

This was a case-series prospective study including 29 consecutive patients with clinically suspected fistulas-in-ano. The standard synergic body coil was used and all patients had T2-weighted SPIR sequences. One radiologist, without prior knowledge of the clinical examination, analysed images and noted the presence of the fistula, its classification and the presence and number of any collections or extensions. The surgeon noted the MRI findings and looked for lesions suggested on MRI. The results of the MRI and surgical assessments were then compared. Results of surgical exploration while the surgeon was aware of MRI results were considered as the gold standard of surgical anatomy.

RESULTS

Twenty-three (79.31%) of 29 fistula tracks were seen on MRI which correctly determined the type of all fistulas. In the six cases where the fistula was not seen on MRI, five were low trans-sphincteric and one was rectovaginal. MRI identified 8 of 10 collections.

CONCLUSION

The synergic body coil MRI with SPIR sequencing without endoanal coils had a high accuracy in the diagnosis of high fistulas collections, complex fistulas and extensions.

Endosonographic imaging of anorectal diseases

OBJECTIVE

The normal sonographic anatomy of the anorectum, sonographic findings of anorectal diseases, and indications and limitations of endosonography compared with magnetic resonance imaging are reviewed. Methods. Endosonographic imaging was performed with a Siemens (Erlangen, Germany) FI 400 ultrasound scanner with an end-fire 7.5-MHz biplane endorectal probe and a B-K Medical (Sandhoften, Denmark) scanner with an 1850 axial-type side-fire 5.0- to 10.0-MHz rotating endoscopic probe.

RESULTS

Rectal carcinoma appears on endorectal sonography as a low-echogenicity lesion that abruptly interrupts the normal sequence of layers. The internal anal sphincter is seen very clearly on endoanal sonography, and it is easy to appreciate atrophy and small tears of this sphincter. Endoanal sonography cannot accurately show thinning of the external anal sphincter. Peroxide-enhanced endoanal sonography is especially useful for patients with recurrent perianal fistulas in whom scarring should be distinguished from recurrent fistulas and detection of the internal opening. However, sonography does not provide an adequate deep and global display of all adjacent pelvic and perineal spaces.

CONCLUSIONS

Endosonography can accurately stage primary rectal tumors and assess the internal anal sphincter. Peroxide-enhanced 3-dimensional imaging can increase the utility of endoanal sonography in detection and characterization of perianal fistulas and planning of optimal therapy. However, magnetic resonance imaging can be used a complementary modality to endosonography, especially for evaluation of external anal sphincter atrophy and deep pelvic inflammation.

Endoanal magnetic resonance imaging of fistula-in-ano: a comparison of STIR with gadolinium-enhanced techniques

PURPOSE

To compare a STIR sequence with gadolinium-enhanced techniques on endoanal magnetic resonance (MR) imaging of fistulas-in-ano by correlating the findings with those at surgery.

MATERIAL AND METHODS

Twenty-two consecutive patients with clinical suspicion of perianal sepsis were studied using an endoanal coil followed immediately by a phased array coil. T1-weighted precontrast and postcontrast and STIR images in transverse and coronal planes were produced with each coil and analysed by noting the presence and site of a collection, primary track, the position of any internal opening, and subcutaneous or supralevator extension. An "expert" and also a "trainee" radiologist assessed the images. Operative findings were similarly recorded. The Fisher exact test was used to compare imaging with surgery. Interobserver variation was calculated using a kappa statistic.

RESULTS

Of 22 patients with suspected fistulas, 8 were simple, 4 were complex, and 3 were superficial sinuses. Five had no anal pathology, 1 had anal excoriation, and 1 had a polyp. At surgery, 6 intersphincteric, 1 transsphincteric, 8 extrasphincteric, no supralevator collections, and 9 internal openings were noted. The overall sensitivity and specificity for detecting these were 75% and 64%, respectively, for STIR imaging, and 58.3% and 62.8% for gadolinium-enhanced imaging. There was good agreement between the "trainee" and the "expert" in the interpretation of images (kappa=0.7).

CONCLUSION

A STIR sequence is more sensitive overall than gadolinium-enhanced techniques on endoanal magnetic resonance imaging of fistulas-in-ano because of increased sensitivity in detecting the internal opening. A combination of endoanal and phased array techniques using STIR imaging sequences is valuable preoperative assessment in both simple and complex cases.

Magnetic resonance imaging of the gastrointestinal tract

Comprehensive bowel examination results from the combined use of T2-weighted single-shot and breath hold T1-weighted gradient echo, minus/plus fat suppression, and gadolinium-enhanced 3D gradient echo (3D VIBE, T1 FAME, 3D THRIVE). Gadolinium-enhanced imaging should be performed dynamically, but the venous 60- to 90-second delayed phase images with fat suppression are generally the most valuable. Removal of fat signal for detection of enhancing normal and abnormal structures is critical. Newly available True-FISP (FIESTA, BFFE) sequences obtained in the 2D form can be very helpful in delineation of bowel wall pathology and overall bowel anatomy, particularly when combined with a water-based intraluminal distending agent. Advantages include rapid acquisition, high signal-to-noise, and motion insensitivity. Generalized protocol for comprehensive evaluation of the entire abdomen and pelvis can be used for the following bowel indications: type and severity of inflammatory bowel disease (IBD); identifying enteric abscesses and fistulae; preoperative staging of malignant neoplasms, including rectal carcinoma; differentiating postoperative and radiation therapy changes from recurrent carcinoma; follow-up evaluation of metastases response to localized ablative or systemic chemotherapy. For improved visualization of bowel wall in dedicated examinations, bowel distension should be achieved using either orally or rectally delivered contrast agents to produce either bright or dark lumen. We have found 2D True-FISP without fat suppression superior to 3D True-FISP and to single-shot echo-train sequences to provide a T2-weighted image of bowel morphology. Strengths include: performed without fat suppression results in the very dark bowel wall being sandwiched between intermediate high signal fat adjacent to bowel serosa, and very high lumen signal from water-distending agent; 2D True-FISP provides motion insensitivity that is lost if 3D is used; True-FISP produces better edge sharpness than single-shot echo-train, higher contrast, and resists flow void artifacts commonly seen with single-shot echo-train imaging combined with a water distending agent. Drawbacks of this technique include: artifacts related to extreme sensitivity to field inhomogeneity, including air-soft tissue interfaces at the patient skin surface, and from retained bowel gas; retained bowel gas is dark against dark bowel wall, impairing bowel wall assessment; and True-FISP does not provide sensitivity for edema, which is superior on single-shot echo-train imaging. Small/large bowel indications for MRI include: inflammatory bowel disease, infectious disease including abscess evaluation or for appendicitis, inflammatory conditions including ischemia, and partial obstruction, malnutrition, and neoplasm search.

Anovaginal Fistulas: Evaluation with Endoanal MR Imaging

PURPOSE

To evaluate endoanal magnetic resonance (MR) imaging in the assessment of anovaginal fistulas and associated findings.

MATERIALS AND METHODS

In a retrospective descriptive study, two radiologists systematically reviewed MR findings in 20 patients with a clinically proved anovaginal fistula and looked for the main fistula tract, the internal opening in the anal canal and/or vagina, secondary fistula tracts, abscesses within the rectovaginal septum, and sphincter damage. Interobserver variability was calculated, and clinical records were searched for possible underlying causes that could explain the complexity of anovaginal fistulas. The kappa value was calculated. Patients with or without a complex anovaginal fistula were compared in regard to the presence of any underlying disease or condition. Statistical significance was calculated with the Fisher exact test.

RESULTS

In all 20 patients, anovaginal fistulas were identified on T2-weighted MR images as predominantly high-signal-intensity linear abnormalities extending between the anal canal and the vagina. In all patients, the fistulas were typically located in the sagittal plane, and the mean distance from the anal verge to the fistula was 25.0 mm (range, 13-32 mm). The internal opening in the anal canal was detected in all patients. The internal opening in the vagina was detected in 19 (95%) patients. In seven (35%) patients, an anovaginal fistula with an additional abnormality was found and included an abscess within the rectovaginal septum (n = 1), a perianal fistula (n = 3), and a perianal fistula in combination with an abscess (n = 3). Defects of the external anal sphincter were present in three (15%) patients. There was complete agreement between observers for all items on endoanal MR images, except for the presence of secondary fistula extensions (agreement, 90%; kappa, 0.74). History of obstetric trauma, pelvic floor surgery, or Crohn disease was present in 10 (50%) patients. Of these patients, six (60%) had a complex anovaginal fistula and four (40%) had a simple anovaginal fistula. In the remaining 10 patients without relevant medical history, one (10%) had a complex anovaginal fistula. This difference tended toward statistical significance (P =.057).

CONCLUSION

Endoanal MR imaging allows evaluation of anovaginal fistulas and additional abnormalities, such as abscesses within the rectovaginal septum, secondary perianal fistula tracts, and sphincter damage.

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.

MR imaging of fistula-in-ano

Accurate preoperative assessment of fistula-in-ano is mandatory if the fistula is not to recur. In recent years, MRI has become pre-eminent for fistula assessment and recent studies have shown that not only is MRI more accurate than surgical assessment, but that surgery based on MRI can reduce further disease recurrence by approximately 75%. The main role of MRI is to alert the surgeon to fistula tracks and extensions that would otherwise have gone undetected and, thus, untreated at the time of surgical assessment under general anaesthetic.

Magnetic resonance imaging for primary fistula in ano

BACKGROUND

This was a prospective study designed to determine the therapeutic impact of magnetic resonance imaging (MRI) in primary fistula in ano, and to assess its effect on outcome.

METHODS

Thirty patients with suspected primary fistula in ano underwent preoperative MRI, and the findings were revealed during surgery following examination under anaesthesia (EUA). Any effect on operative approach was noted. Outcome was assessed at a median of 12 months.

RESULTS

Two patients had sinuses, one had no sepsis and 27 had fistulas: five superficial, seven intersphincteric, 14 trans-sphincteric and one suprasphincteric. MRI and EUA agreed in 15 patients and MRI findings altered the surgical approach in a further three (10 per cent); two of the latter patients were believed to have a sinus at EUA, which MRI correctly identified as a fistula, allowing definitive treatment. The therapeutic impact of MRI was therefore 10 per cent. Persisting disagreement between MRI and EUA in 12 patients mostly related to minor discrepancies in classification. Only one patient required further unplanned surgery, which was for skin-bridging rather than any new sepsis.

CONCLUSION

In experienced hands, MRI has a therapeutic impact of 10 per cent for primary fistula in ano, precipitating surgery that is likely to reduce recurrence in a small, but important, proportion of patients.

Imaging anal fistula

The management of fistula-in-ano has been based on digital examination and operative findings. MR imaging has shown significant limitations to this approach, particularly in the management of recurrent fistula. The most cost-effective approach may be using a combination of endosonography and MR imaging. Preoperative confirmation of fistula complexity facilitates surgery planning of sphincter saving techniques and prevents sepsis being missed, which has been shown to reduce recurrence. Imaging has a significant role to play in this condition to improve patient outcome.

The role of anal ultrasound in the management of anal fistulas

OBJECTIVE: To assess the accuracy of anal ultrasound (AUS) for anal fistulas, and the impact of routine pre-operative AUS on their surgical management. METHODS: Pre-operative AUS was performed in 38 consecutive patients with an anal fistula using a 10-MHz Brüel & Kjaer probe. All patients underwent subsequent examination under anaesthetic (EUA) with documentation of the anatomy of the fistula before the surgeon was shown the AUS results. Agreement between AUS and EUA findings and any modification to the surgical treatment was recorded. RESULTS: There was 84% agreement between AUS and EUA findings regarding presence and site of fistulas. One fistula not seen at AUS was found at EUA, and 5 fistulas seen on AUS were not demonstrated at EUA. AUS influenced the surgery undertaken in 9/24 (38%) patients; demonstrating occult sphincter defects (2 patients), reclassifying fistulas from low to higher fistulas (3 patients), deciding a surgical treatment open to doubt (2 patients) and helping identify an obscure fistula not initially found at EUA (2 patients). CONCLUSIONS: Accuracy of AUS in the assessment of anal fistulas is confirmed. Operative management is influenced in 38% of cases, usually towards more conservative treatment. We recommend the use of pre-operative AUS in the assessment of anal fistulas.

Imaging of anorectal disease

BACKGROUND

Over the past two decades developments in imaging have changed the assessment of patients with anorectal disease.

METHODS

The literature on imaging techniques for anorectal diseases was reviewed over the period 1980-1999.

RESULTS

For the staging of primary rectal tumours, phased array magnetic resonance imaging (MRI) may be regarded as the most appropriate single technique. The combination of endosonography or endoluminal MRI with ultrasonography or spiral computed tomography yields similar results. All techniques have limitations both for local staging and in the assessment of distant metastases. MRI or positron emission tomography is preferable for tumour recurrence. For perianal fistula, high-resolution MRI (phased array or endoluminal) is the technique of choice. For constipation, defaecography is the preferred technique, nowadays with emphasis on functional information. The role of magnetic resonance defaecography is currently being evaluated. For faecal incontinence, endosonography and endoluminal MRI give similar results in detecting sphincter defects; endoluminal MRI has the advantage of detecting external sphincter atrophy.

CONCLUSION

High-resolution MRI, endosonography and defaecography are currently the optimal imaging techniques for anorectal disease.

External anal sphincter atrophy on endoanal magnetic resonance imaging adversely affects continence after sphincteroplasty

BACKGROUND

There is still considerable debate about the value of preoperative anorectal physiological parameters in predicting the clinical outcome after sphincteroplasty. Recently it has been reported that atrophy of the external anal sphincter can be clearly shown with endoanal magnetic resonance imaging (MRI). The aims of this study were to investigate the prevalence of external anal sphincter atrophy in women with anterior sphincter defects due to obstetric injury and to determine the impact of external anal sphincter atrophy on the outcome of sphincteroplasty.

METHODS

In this prospective study, 20 consecutive women (median age 50 (range 28-75) years) with faecal incontinence due to obstetric trauma were assessed before operation with endoanal ultrasonography and endoanal MRI. The external anal sphincter was examined and evaluated for the presence of atrophy. The clinical outcome of sphincteroplasty was interpreted without knowledge of the magnetic resonance and ultrasonographic images.

RESULTS

In all patients anterior sphincter defects could be demonstrated with ultrasonography and MRI. External anal sphincter atrophy could only be demonstrated on MRI. Eight of 20 patients had external anal sphincter atrophy. Continence was restored in 13 patients. Outcome was significantly better in those without external anal sphincter atrophy (11 of 12 patients versus two of eight; P = 0.004).

CONCLUSION

External anal sphincter atrophy can only be visualized on endoanal MRI and affects continence after sphincteroplasty. Endoanal MRI is valuable in the preoperative assessment of patients with faecal incontinence. Presented to the American Society of Colon and Rectal Surgeons in Philadelphia, Pennsylvania, USA, June 1997

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.

Endoluminal MR imaging of diseases of the anus and rectum

Endoluminal MRI of the rectum and anus was introduced in the first half of this decade to overcome the limitations of endoluminal sonography and body coil MRI. Endoluminal MRI is the imaging method of choice for fecal incontinence and anal tumors, whereas it is a competitive imaging method to phased array coil MRI in patients with perianal fistulas or rectal tumor. The purpose of this article is to describe the technique and major indications of endoluminal MR imaging of the anus and rectum.

Esophageal carcinoma. Ex vivo endoluminal magnetic resonance imaging

RATIONALE AND OBJECTIVES

The authors evaluate ex vivo the role of endoluminal magnetic resonance imaging (MRI) in the tumor and regional lymph node staging of esophageal carcinoma.

MATERIALS AND METHODS

Nine esophagus specimens with carcinoma (seven adenocarcinoma, two squamous cell carcinoma) were studied directly after resection. Tumor (T) and regional lymph nodes (N) were classified, and the results were compared to histopathology.

RESULTS

T classification with endoluminal MRI was correct in eight of the nine tumors. One Tis tumor was staged as T1 tumor because of submucosal edema. MRI detected 35 of 91 lymph nodes. Of these 35 nodes, 14 were true-positives, 5 were false-positives, 1 was a false-negative, and 15 were true-negatives. The majority of the 56 missed lymph nodes were outside the field of view, including two specimens with a tight stricture. These lymph nodes included seven nodes with metastatic involvement. TN classification was correct in six specimens (67%).

CONCLUSION

This ex vivo pilot study demonstrates that T classification of esophageal carcinoma using endoluminal MRI is feasible. The results of lymph node classification are less favorable, predominantly because of the limited field of view.

Imaging studies of the pelvic floor

A variety of imaging modalities complement the history and physical examination in the investigation of pelvic floor dysfunction in women. Current fluoroscopic techniques, including defocography, can reveal underlying pelvic floor defects by reproducing normal daily activities that cause symptoms. Magnetic resonance imaging provides fine musculoskeletal detail of this region in anatomic plane not well seen via computerized tomography. Ultrasound is used primarily in assessment of the anal sphincter muscles. Cystourethroscopy provides direct visualization of the lower urinary tract. This article describes the clinical applications and technique of each modality.

MRI of pouch-related fistulas in ulcerative colitis after restorative proctocolectomy

PURPOSE

Our purpose was to determine the value of MRI in diagnosing pouch-related fistulas in patients with ulcerative colitis and to compare pulse sequences with and without contrast enhancement in their performance of visualization.

METHOD

Forty-four patients with pelvic symptoms after restorative proctocolectomy underwent MRI. All 26 patients with pouch-related fistulas were treated surgically; 18 patients with pouchitis were treated conservatively. MRI was performed at 1.0 T with T1-weighted FLASH sequences before and after administration of Gd-DTPA, T2-weighted and proton density-weighted turbo SE sequences, and a T2-weighted fat saturation sequence. Images were analyzed for the presence of fistula; pulse sequences were additionally compared for best visualization on a four point scale of diagnostic confidence.

RESULTS

MRI detected 23 of 26 cases of fistulas; there were no false-positive diagnoses. Surgery revealed fistulas in three cases in which no pathology was found on MRI. Two patients had a short sinus tract at the pouch-anal anastomosis, and a third patient had a pouch-vaginal fistula. The Gd-enhanced FLASH sequence obtained the highest score, and second best was the T2-weighted fat saturation technique.

CONCLUSION

MRI is a valuable technique for diagnosing pouch-related fistulas, However, there are limitations in detection of short sinus tracts and pouch-vaginal fistulas. Highest diagnostic confidence is obtained with a Gd-enhanced FLASH sequence, which might be helpful after pelvic surgery or if the fact saturation technique is equivocal.

MRI of fistula-in-ano: a comparison of endoanal coil with external phased array coil techniques

PURPOSE

The objective of our study was to compare MRI of fistulas-in-ano using an endoanal coil with that using a pelvic phased array coil and to assess the value of a combined approach by correlating the findings with those at surgery.

METHOD

Twenty consecutive patients with clinical suspicion of perianal sepsis were studied using an endoanal coil immediately followed by a phased array coil. T1 weighted and STIR images in transverse and coronal planes were made with each coil and analysed by noting the presence and site of a collection and primary track, the position of any internal opening, and subcutaneous or supralevator extension. Operative findings were similarly recorded.

RESULTS

Of 20 patients with suspected fistulas, 8 had simple fistulas, 8 had complex fistulas, and 4 had no current evidence of infection. The concordance between MR and surgery for identifying the presence and site of the collection, the primary track, and the internal opening in both simple and complex cases was superior using the endoanal coil as compared with the phased array. Both coils together reflected the findings of the endoanal coil used alone. However, for supralevator/subcutaneous extension, concordance was superior using the phased array compared with the endoanal coil, and a combined approach reflected the values of the phased array coil used alone.

CONCLUSION

Endoanal MRI is highly sensitive in the delineation of fistulas-in-ano. In combination with phased array techniques, it provides valuable preoperative assessment in both simple and complex cases.

Magnetic resonance imaging of fistula-in-ano: STIR or SPIR?

Patients with clinically suspected anorectal sepsis were studied using MRI in order to determine if T2 weighted sequences with fat suppression conveyed any additional benefit over conventional short tau inversion recovery (STIR) sequences. 23 consecutive patients (16 male) undergoing MRI for suspected perianal sepsis were studied prospectively using a 1.0 T whole body system and body coil. Axial and coronal T1 weighted turbo spin echo sequences were obtained, followed by STIR and T2 weighted spectral fat saturation inversion recovery (SPIR) sequences. Images were assessed for the presence of sepsis or fistula, and information provided by the sequences compared. Active disease was diagnosed in 17 patients, 14 of whom had fistula-in-ano; one intersphincteric, 10 transsphincteric and three extrasphincteric. Internal openings were identified in all of these 14 patients; anal in 10, rectal in two, and both in two. Diagnosis and fistula classification was possible in all of these 14 subjects on the basis of STIR sequences alone. The anal sphincters and pelvic floor musculature were better resolved by STIR than SPIR, leading to easier and more confident determination of fistula anatomy in eight of the 14 (57%). In no case did STIR sequences fail to resolve inflammation seen subsequently on SPIR, despite reduced track intensity. T1 weighted sequences were generally non-contributory. Both STIR and SPIR sequences are adequate to classify fistula-in-ano, but classification was easier with STIR due to superior resolution of pelvic floor structures.

Rectal perflubron: new application in MRI of perirectal fistulae

PURPOSE

Our goal was to determine the efficacy of MRI with rectal administration of perflubron in the evaluation of perirectal and pelvic fistulae, with an emphasis on development of an improved method for fistula visualization.

METHOD

Fourteen pelvic and/or perirectal fistulae were evaluated in nine patients with MRI after the rectal administration of 200 ml of perflubron. Images were reviewed by two independent readers and evaluated for the presence or absence of fistulae. Qualitative assessment was also performed, rating the examinations for the ability to visualize the fistulae. Comparison was made with the clinical examination and/or operative findings, as well as available preperflubron imaging studies (CT = 10; fluoroscopy = 1; preperflubron MRI = 4).

RESULTS

MRI with rectal perflubron demonstrated all 14 fistulae (100%), while preperflubron imaging demonstrated only 7 of 14 (50%) fistulae (p < or = 0.008, Wilcoxon signed rank test). In addition, MRI with perflubron resulted in significantly improved qualitative visualization of fistulae (overall very good rating versus poor rating for preperflubron imaging, p < or = 0.006, Wilcoxon signed rank test).

CONCLUSION

MRI with rectal perflubron is a superior modality for imaging of fistulae, compared with conventional methods, since it allows a noninvasive means of demonstrating the presence of a fistula as well as offers improved qualitative assessment of fistulous disease.

Magnetic resonance imaging of the female pelvic floor and urethra: body coil versus endovaginal coil

The anatomy of the female pelvic floor and urethra is complex. With the introduction of MRI, the discussion about the normal anatomy of this area has not diminished. The use of a body coil may be contributary to this. In the present study images obtained with an endovaginal coil are compared with those of a quadrature body coil series to study the possible advantage of endovaginal imaging. Axial and radial T2-w TSE images at a 1.0-T machine were obtained in seven healthy volunteers. The pelvic floor structures as well as the levator ani muscle and the urogenital diaphragm are excellently demonstrated with the endovaginal coil. Also, the urethrovaginal sphincter could be recognized in six volunteers, but only in three with the body coil. In six volunteers a new ligamentous structure, the urethropelvic sling, connecting the urethra to the levator ani muscle and contributing to the supporting mechanism of the urethra is shown with the endovaginal coil. The zonal anatomy of the urethra is excellently shown with the endovaginal coil. The urethral length could only be accurately measured with this coil and ranged from 3.1 to 3.6 cm. Compared with the body coil, endovaginal MRI is excellent in demonstrating the anatomy of the pelvic floor and urethra.