A step towards stereotactic navigation during pelvic surgery: 3D nerve topography

Background

Long-term morbidity after multimodal treatment for rectal cancer is suggested to be mainly made up by nerve-injury-related dysfunctions. Stereotactic navigation for rectal surgery was shown to be feasible and will be facilitated by highlighting structures at risk of iatrogenic damage. The aim of this study was to investigate the ability to make a 3D map of the pelvic nerves with magnetic resonance imaging (MRI).

Methods

A systematic review was performed to identify a main positional reference for each pelvic nerve and plexus. The nerves were manually delineated in 20 volunteers who were scanned with a 3-T MRI. The nerve identifiability rate and the likelihood of nerve identification correctness were determined.

Results

The analysis included 61 studies on pelvic nerve anatomy. A main positional reference was defined for each nerve. On MRI, the sacral nerves, the lumbosacral plexus, and the obturator nerve could be identified bilaterally in all volunteers. The sympathetic trunk could be identified in 19 of 20 volunteers bilaterally (95%). The superior hypogastric plexus, the hypogastric nerve, and the inferior hypogastric plexus could be identified bilaterally in 14 (70%), 16 (80%), and 14 (70%) of the 20 volunteers, respectively. The pudendal nerve could be identified in 17 (85%) volunteers on the right side and in 13 (65%) volunteers on the left side. The levator ani nerve could be identified in only a few volunteers. Except for the levator ani nerve, the radiologist and the anatomist agreed that the delineated nerve depicted the correct nerve in 100% of the cases.

Conclusion

Pelvic nerves at risk of injury are usually visible on high-resolution MRI with dedicated scanning protocols. A specific knowledge of their course and its application in stereotactic navigation is suggested to improve quality of life by decreasing the likelihood of nerve injury.

Electronic supplementary material

The online version of this article (10.1007/s00464-018-6086-3) contains supplementary material, which is available to authorized users.

Herniation of the colon through the foramen of Winslow-A case report

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Herniation is rare and diagnostic delay increases mortality and morbidity.

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Patients present with nonspecific acute abdominal pain.

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Computed tomography helps early diagnosis and could thereby prevent bowel ischemia.

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Herniation can be reversed laparoscopically without bowel resection in case of early diagnosis.

Introduction

Herniation of the bowel through the foramen of Winslow is a rare condition presenting with acute abdominal pain. Diagnostic delay often results in high morbidity and mortality.

Case presentation

A patient presented with right sided acute abdominal pain. Computed tomography showed herniation of the ascending colon through the foramen of Winslow which could be reversed laparoscopically without the need for bowel resection. There were no postoperative complications and no recurrences have occurred to date.

Discussion

Bowel herniation through the foramen of Winslow is very rare, comprising only 8% of all internal herniations. Historically, the majority of cases was diagnosed intra-operatively and bowel resection was necessary because of ischemia. With the introduction of computed tomography, the diagnosis can be made earlier, possibly resulting in a lower morbidity and mortality rate.

Conclusion

Herniation through the foramen of Winslow is a rare condition. Patients will present with sudden onset abdominal pain. Early imaging helps to recognize the diagnosis and could prevent bowel ischemia.

High-resolution endovaginal MR imaging in stress urinary incontinence

The causes of stress urinary incontinence are not completely known. Recent papers have stressed the importance of more anatomical information, which may help to elucidate the mechanism of stress urinary incontinence. The purpose of this study was to evaluate the prevalence of lesions of the urethral support mechanism and lesions (defects and scars, thinning) of levator ani muscle with endovaginal MRI in a case-control study. Forty women (median age 52 years, age range 40-65 years)--20 patients with stress urinary incontinence (cases) and 20 age-matched healthy volunteers (controls)--underwent endovaginal MRI: axial, coronal, and sagittal T2-weighted turbo spin echo. The examinations were evaluated for the presence of lesions of urethral supporting structures and levator ani and scar tissue of the levator ani. The thickness of the levator ani muscle was measured. Lesions of the urethral support system and levator ani were significantly more prevalent in cases than in controls ( p<0.01). Median levator ani thickness in patients was significantly lower than in healthy controls [2.5 mm (range 0.9-4.1 mm) vs 3.9 mm (range 1.4-7 mm)] ( p<0.01). This study indicates a relationship between stress urine incontinence and the presence of lesions of the urethral support and levator ani and levator ani thinning.

Anovaginal and rectovaginal fistulas: endoluminal sonography versus endoluminal MR imaging

OBJECTIVE

The exact location of anovaginal and rectovaginal fistulas cannot be determined by physical examination and conventional techniques. The objective of our study was to compare the accuracy of endoluminal sonography and endoluminal MR imaging in revealing the location of anovaginal and rectovaginal fistulas.

MATERIALS AND METHODS

Nineteen consecutive patients (age range, 28-56 years; median age, 39 years) with clinical indications of an anovaginal or rectovaginal fistula were included in our retrospective study. Endoluminal sonography was performed using a 7.5-MHz transducer. Endoluminal MR imaging was performed at 0.5 T for 10 patients and 1.5 T for nine patients; axial T2-weighted gradient-echo, coronal and sagittal T2-weighted turbo spin-echo (0.5 T), or axial and radial T2-weighted turbo spin-echo and axial T2-weighted fat saturated turbo spin-echo (1.5 T) images were obtained. For a variety of reasons, surgery of the fistula was not attempted in six of these 19 patients. The imaging findings were compared with the findings obtained during surgery in the remaining 13 patients.

RESULTS

In 12 of the 13 patients, the fistula was found during surgery: seven of the fistulas were anovaginal, and five were rectovaginal. Findings of endoluminal sonography were true-positive in 11 patients, true-negative in one, and false-negative in one. Findings of endoluminal MR imaging were true-positive in 11 patients, false-negative in one, and false-positive in one. Positive predictive value for endoluminal sonography and endoluminal MR imaging were 100% and 92%, respectively. Imaging findings for anal sphincter defects were comparable.

CONCLUSION

Endoluminal sonography and endoluminal MR imaging have comparable positive predictive values in revealing the location of anovaginal and rectovaginal fistulas.

Normal anal sphincter anatomy and age- and sex-related variations at high-spatial-resolution endoanal MR imaging

PURPOSE

To describe the various patterns of normal sphincter anatomy as seen at endoanal magnetic resonance (MR) imaging and to assess sex- and age-related variations in the dimensions of the anal sphincter to refine the diagnosis of sphincter disorders.

MATERIALS AND METHODS

Endoanal MR imaging (1.5 T) was performed in 100 healthy volunteers (50 women, 50 men) evenly distributed between ages 20 and 85 years. The essential anatomic structures were evaluated, and various patterns in men and women were recorded. The thickness of the anal sphincter muscles and the length of the anal canal were measured, and age- and sex-related correlations were studied.

RESULTS

Sex-related differences included a significantly shorter external sphincter in women than in men both laterally (mean, 27.1 mm +/- 5.4 vs 28.6 mm +/- 4.3; P: <.05) and anteriorly (mean, 14.0 mm +/- 3.0 vs 27.0 mm +/- 53.0; P: <.051). The superficial transverse perineal muscle is located more superiorly in women than in men. The central perineal tendon in men is a central muscular insertion point; in women, it represents an area where muscle fibers imbricate. Age-related variations included a significant decrease in the thickness of the external sphincter in men (P: <.01). Significant decrease in the thickness of the longitudinal muscle and increase in the thickness of the internal sphincter were noted in both sexes (P: <.01).

CONCLUSION

High-spatial-resolution endoanal MR imaging provides excellent visualization of pelvic floor structures. Severe atrophy as it occurs in incontinent patients should be differentiated from physiologic, age-related thinning of the external sphincter and longitudinal muscle.

Relationship between sphincter morphology on endoanal MRI and histopathological aspects of the external anal sphincter

Atrophy of the external anal sphincter can be shown only on endoanal magnetic resonance imaging (MRI). Until now no study has compared the morphological endoanal MRI findings with histopathological aspects of the external anal sphincter. The aim of this study was to validate the MRI interpretation of the external anal sphincter using histology as a "gold standard." In this prospective study 25 consecutive unselected women (median age 48 years, range 27-72) with fecal incontinence due to obstetric trauma were assessed preoperatively with endoanal MRI. All patients underwent anterior sphincteroplasty within 6 months of the preoperative assessment. During sphincter repair, a biopsy specimen was taken both from the left and right lateral parts of the external anal sphincter. Interpretation of MRI was performed by one of the radiologists (J.S.), and biopsy specimens were evaluated by the pathologist (W.J.M.). Both were blinded to the interpretation of the other. MRI revealed external anal sphincter atrophy in 9 of the 25 patients (36%). Histopathological investigation confirmed these findings in all but one. In one additional patient atrophy was detected on histological investigation while the morphology of the external anal sphincter was classified as normal on MRI. In detecting sphincter atrophy endoanal MRI showed 89% sensitivity, 94% specificity, 89% positive predictive value, and 94% negative predictive value. MRI correctly identified sphincter morphology in 23 of 25 cases (92%). This study demonstrates that endoanal MRI accurately identifies normal and abnormal external anal sphincter morphology. Endoanal MRI is therefore a valuable preoperative diagnostic tool.

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

Endoanal MR imaging of the anal sphincter in fecal incontinence

Fecal incontinence is a major medical and social problem. The most frequent cause is a pathologic condition of the anal sphincter. Endoanal magnetic resonance (MR) imaging allows detailed visualization of the normal anatomy and pathologic conditions of the anal sphincter. The hyperintense internal sphincter appears as a continuation of the smooth muscle of the rectum; the hypointense external sphincter surrounds the lower part of the internal sphincter. A sphincteric defect is seen as a discontinuity of the muscle ring. Scarring appears as a hypointense deformation of the normal pattern of the muscle layer. Two external sphincteric patterns may be misdiagnosed as defects: a posterior discontinuity (often seen in young male patients) and an anterior discontinuity (often seen in female patients). Atrophy of the external sphincter is easily detected on coronal MR images by comparing the thicknesses of all anal muscles. Endoanal MR imaging is superior to endoanal ultrasonography because of the multiplanar capability and higher inherent contrast resolution of the former. Use of endoanal MR imaging may lead to better selection of candidates for surgery and therefore better surgical results. Endoanal MR imaging is the most accurate technique for detection and characterization of sphincteric lesions and planning of optimal therapy.

Fecal incontinence: endoanal US versus endoanal MR imaging

PURPOSE

To assess endoanal ultrasonography (US) and endoanal magnetic resonance (MR) imaging for mapping of anal sphincter defects that have been validated at surgery in patients with fecal incontinence.

MATERIALS AND METHODS

US, MR imaging, and surgical findings in 22 women with fecal incontinence who underwent sphincter repair were retrospectively reviewed. US and MR imaging had been performed before surgery. The findings were evaluated separately and validated with surgical results.

RESULTS

Endoanal MR imaging findings showed better agreement with surgical results than did endoanal US findings for diagnosis of lesions of the external sphincter (kappa value, 0.85 vs 0.53) and of the internal sphincter (kappa value, 0.64 vs 0.49). Endoanal US could not accurately demonstrate thinning of the external sphincter. MR imaging results correlated moderately with US results (kappa = 0.39). If endoanal MR images alone had been considered, the correct surgical decision would have been made in 21 (95%) patients; if endoanal US images alone had been considered, the correct decision would have been made in 17 (77%) patients.

CONCLUSION

MR imaging is more accurate than US for demonstration of sphincter lesions. MR imaging provides higher spatial resolution and better inherent image contrast for lesion characterization. Endoanal MR imaging allows more precise description of the extent and structure of complex lesions and is superior for help in decisions about optimal therapy.

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.