MRI morphology of the levator ani muscle, endopelvic fascia, and urethra in women with stress urinary incontinence

The relationship between bladder functions, pelvic floor muscle strength, fall, and fatigue in multiple sclerosis

BACKGROUND

The aim of this study was to determine the relationship between the severity of bladder functions, fatigue, quality of life (QoL), fall, and pelvic floor muscle strength in patients with Multiple Sclerosis (PwMS).

METHODS

Patients were divided into two groups according to their Expanded Disability Status Scale (EDSS) bladder scores as Group 1 (EDSS bladder score 0-1, mildly affected group, n = 25) and Group 2 (EDSS bladder score 2-3-4, moderate and severely affected group, n = 21). Pelvic floor muscle (PFM) strength (EMG-Biofeedback device), fear of fall (Fall Efficacy Scale (FES-1)), fatigue (Fatigue Severity Scale (FSS)), QoL (Urogenital Distress Inventory-short form (UDI-6), and Incontinence Impact Questionnaire-short form (IIQ-7)) were evaluated.

RESULTS

46 female patients diagnosed with MS were included in this study. No significant differences in baseline characteristics were seen between the groups except age. EDSS bladder score were 1 (0-1) and 3 (2-4), EMG-Biofeedback score were 79,5 ± 8,11 and 41,7 ± 5,48, FSS score were 38,7 ± 2,80 and 54±2,20, FES-I score were 16,9 ± 2,15 and 40,2 ± 7,39, UDI-6 score were 4,24±0,47 and 8,42±0,64, IIQ-7 score were 3,64±0,86 and 18,2 ± 1,42 in Group 1 and Group 2. As a result of statistical analysis, significant differences were found in less fatigue and fall, higher PFM strength and better QoL with mildly affected PwMS (p<0,05).

CONCLUSION

There was a significant difference in terms of bladder function level in PFM strength, fall, fatigue and QoL between the mildly affected group and the moderate and severely affected group.

Evaluating changes in the strength of the levator ani muscle after vaginal delivery using T2-parameter mapping

OBJECTIVE

To evaluate pelvic floor muscle injury in patients with levator ani muscle (LAM) weakness after vaginal delivery using T2-parameter mapping.

MATERIALS AND METHODS

40 parturients (patient group) and 25 nonparturients (healthy control group) were enrolled in the study. The LAM weakness group had a Modified Oxford Grading System (MOGS) grade of less than 3 after vaginal delivery. All participants underwent pelvic magnetic resonance imaging (MRI) scans, including T2 and T2* mapping, on which the main branches of the LAM, the puborectalis and iliococcygeus, were evaluated. The differences in T2 and T2* values in the puborectalis and iliococcygeus between patients with LAM weakness and controls were analyzed using an independent samples t test or a Mann-Whitney U test.

RESULTS

For both the right and left iliococcygeus, the T2* values of the patient group were lower than those of the control group (P = 0.002 and 0.008, respectively), while no significant difference was observed in the T2 values between the groups (P = 0.45 and 0.69, respectively). For both the right and left puborectalis, no significant differences in the T2* (P = 0.25 and P = 0.25, respectively) or T2 values (P = 0.38 and 0.43, respectively) were observed between the patient and control groups.

CONCLUSION

T2* mapping as a quantitative measurement is an effective imaging tool to assess LAM injury in women after vaginal delivery. The iliococcygeus was more susceptible to vaginal delivery damage than the puborectalis, and pelvic floor dysfunction may be mainly driven by iliococcygeus injury.

The Anatomical Pathogenesis of Stress Urinary Incontinence in Women

Stress urinary incontinence is a common disease in middle-aged and elderly women, which seriously affects the physical and mental health of the patients. For this reason, researchers have carried out a large number of studies on stress urinary incontinence. At present, it is believed that the pathogenesis of the disease is mainly due to changes related to age, childbirth, obesity, constipation and other risk factors that induce changes in the urinary control anatomy, including the anatomical factors of the urethra itself, the anatomical factors around the urethra and the anatomical factors of the pelvic nerve. The combined actions of a variety of factors lead to the occurrence of stress urinary incontinence. This review aims to summarize the anatomical pathogenesis of stress urinary incontinence from the above three perspectives.

Hypothesis generation: Quantitative research to levator ani muscle injury based on MRI texture analysis

AIM

Patients with pelvic organ prolapse (POP) mostly have injury to the levator ani muscle (LAM). We aimed to assess LAM injury in POP patients by quantifying texture feature (TF) ratios between the LAM and the obturator internus muscle (OIM) using texture analysis.

METHODS

This study retrospectively enrolled 32 participants, including 24 patients with POP and eight people with normal pelvic floor muscles. TFs of the LAM and the OIM were extracted using LIFEx version 6.30, and an independent samples t-test was performed to determine TF ratios characterizing LAM injury. After dimension reduction and binary logic analysis, the optimal TF ratio was obtained and the LAM injury quantitative evaluation was proposed. Spearman's correlation was performed to explore the correlations between TF ratios and clinical characteristics. We compared the diagnostic performance of quantitative evaluation and visual evaluation.

RESULTS

There were significant differences in 13 TF ratios between the POP and control groups. The area under the receiver operating characteristic curve of the integrated TF ratio was 0.948. Integrated TF ratio was significantly correlated with body mass index, pregnancies, and vaginal deliveries but had no correlation with LAM volume, hiatal area or abortions. Compared with the visual evaluation, the diagnostic accuracy of the quantitative evaluation had improved by 63.2% and 14.3% in the "minor defect" and "major defect" categories, respectively.

CONCLUSION

The integrated TF ratio can be used as a new quantifiable index to characterize LAM injury. The TF evaluation provides a potential role in LAM injury noninvasive diagnostic.

Usefulness of transperineal shear wave elastography of levator ani muscle in women with stress urinary incontinence

This study aimed to quantitatively assess the quality of levator ani muscle (LAM) using shear wave elastography (SWE) and to evaluate the association between the elasticity of LAM and stress urinary incontinence (SUI). The study population included 32 women with SUI and 34 women with normal pelvic support. The thickness of LAM, bladder neck descent (BND), and urethral funneling (UF) were assessed by transperineal ultrasound. LAM elasticity was measured by SWE at rest and during the maximal Valsalva maneuver. Age, menopause, BND, and UF showed a positive correlation with SUI. There was no significant between-group difference in the elastic modulus values of LAM at rest. The thickness of LAM in women with SUI was greater than that in control group at rest and during the maximal Valsalva maneuver (P < 0.001). The elastic modulus values of E_max and E_mean were significantly increased from rest to the maximal Valsalva maneuver in all participants (56.24 vs 82.43 kPa and 47.92 vs 72.37 kPa, P < 0.001). The change of these variables from rest to the maximal Valsalva maneuver in the control group was more obvious than that in the SUI group (34.09 vs 17.87 kPa and 31.55 vs 16.82 kPa, P < 0.05). The elasticity of LAM, as quantified by SWE, may potentially be used as an index for predicting SUI.

ACR Appropriateness Criteria® Pelvic Floor Dysfunction in Females

Pelvic floor disorders including pelvic organ prolapse (POP), urinary dysfunction, defecatory dysfunction, and complications after pelvic floor surgery are relatively common in the female population. Imaging tests are obtained when the initial clinical evaluation is thought to be incomplete or inconclusive or demonstrates findings that are discordant with patients' symptoms. An integrated imaging approach is optimal to evaluate the complex anatomy and dynamic functionality of the pelvic floor. Fluoroscopic cystocolpoproctography (CCP) and MR defecography are considered the initial imaging tests of choice for evaluation of POP. Fluoroscopic voiding cystourethrography is considered the initial imaging test for patients with urinary dysfunction. Fluoroscopic CCP and MR defecography are considered the initial imaging test for patients with defecatory dysfunction, whereas ultrasound pelvis transrectal is a complementary test in patients requiring evaluation for anal sphincter defects. MRI pelvis without and with intravenous contrast, MRI pelvis with dynamic maneuvers, and MR defecography are considered the initial imaging tests in patients with suspected complications of prior pelvic floor surgical repair. Transperineal ultrasound is emerging as an important imaging tool, in particular for screening of pelvic floor dysfunction and for evaluation of midurethral slings, vaginal mesh, and complications related to prior pelvic floor surgical repair. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Inverse correlation between urethral length and continence before and after native tissue pelvic floor reconstruction

Urethral length was evaluated retrospectively in patients with prolapse undergoing anterior native-tissue repair. Effects of age, prolapse stage, defect pattern, urodynamic and clinical stress test findings, and tension-free vaginal tape (TVT) surgery indication were analyzed using Mann-Whitney and Wilcoxon tests and linear and logistic regression. Of 394 patients, 61% had stage II/III and 39% had stage IV prolapse; 90% of defects were central (10% were lateral). Median pre- and postoperative urethral lengths were 14 and 22 mm (p < 0.01). Preoperative urethral length was greater with lateral defects [p < 0.01, B 6.38, 95% confidence interval (CI) 4.67-8.08] and increased stress incontinence risk (p < 0.01, odds ratio 1.07, 95% CI 1.03-1.12). Postoperative urethral length depended on prolapse stage (p < 0.01, B 1.61, 95% CI 0.85-2.38) and defect type (p = 0.02, B - 1.42, 95% CI - 2.65 to - 0.2). Postoperatively, TVT surgery was indicated in 5.1% of patients (median 9 months), who had longer urethras than those without this indication (p = 0.043). Native-tissue prolapse repair including Kelly plication increased urethral length, reflecting re-urethralization, particularly with central defects. The functional impact of urethral length in the context of connective tissue aging should be examined further.

MR defecography in the assessment of anatomic and functional abnormalities in stress urinary incontinence before and after pelvic reconstruction

PURPOSE

Magnetic resonance defecography (MRD) was used to evaluate anatomic and functional pelvic floor disorders in women with stress urinary incontinence (SUI) before and after midurethral sling (MUS) intervention.

METHOD

We performed MRD in both SUI patients and continent controls. Static MR was used to describe the anatomic abnormalities in levator ani muscle and periurethral ligaments (PUL). Dynamic MR was used to depict the function of the urethra and pelvic floor. We compared the MRD parameters between the SUI patients and continent controls before surgery. For SUI patients, dynamic MR images evaluated the functional changes of the urethra and pelvic floor after surgery.

RESULTS

In SUI group, 75.8 % have PUL defects, 65.7 % discontinuity or complete loss of pubococcygeal muscle, as compared to the continent groups (p < 0.01). There was no significant difference between the perimenopausal volunteers and SUI patients in the puborectalis defection (p > 0.05). The dynamic MR showed the urethral hypermobility, functional urethra shortening, bladder neck funneling, urethra opening and cystocele were significantly associated with SUI patients (p < 0.01). Postoperative MR indicated that SUI patients after MUS had a lower risk of bladder funneling and urethral opening at the defection phase (p < 0.01), but no significant difference in urethral hypermobility or pelvic floor prolapse was seen (p>0.05).

CONCLUSIONS

MRD with high-resolution and defecation phases provides a detailed anatomic and functional evaluation of the pelvic floor in female SUI before and after pelvic reconstruction.

Recommended standardized terminology of the anterior female pelvis based on a structured medical literature review

BACKGROUND

The use of imprecise and inaccurate terms leads to confusion amongst anatomists and medical professionals.

OBJECTIVE

We sought to create recommended standardized terminology to describe anatomic structures of the anterior female pelvis based on a structured review of published literature and selected text books.

STUDY DESIGN

We searched MEDLINE from its inception until May 2, 2016, using 11 medical subject heading terms to identify studies reporting on anterior female pelvic anatomy; any study type published in English was accepted. Nine textbooks were also included. We screened 12,264 abstracts, identifying 200 eligible studies along with 13 textbook chapters from which we extracted all pertinent anatomic terms.

RESULTS

In all, 67 unique structures in the anterior female pelvis were identified. A total of 59 of these have been previously recognized with accepted terms in Terminologia Anatomica, the international standard on anatomical terminology. We also identified and propose the adoption of 4 anatomic regional terms (lateral vaginal wall, pelvic sidewall, pelvic bones, and anterior compartment), and 2 structural terms not included in Terminologia Anatomica (vaginal sulcus and levator hiatus). In addition, we identified 2 controversial terms (pubourethral ligament and Grafenberg spot) that require additional research and consensus from the greater medical and scientific community prior to adoption or rejection of these terms.

CONCLUSION

We propose standardized terminology that should be used when discussing anatomic structures in the anterior female pelvis to help improve communication among researchers, clinicians, and surgeons.

Association between Magnetic Resonance Imaging Findings of the Pelvic Floor and de novo Stress Urinary Incontinence after Vaginal Delivery

Objective

The study aimed to evaluate the contributions of levator ani muscle (LAM) injury, vesical neck movement, urethral length and mobility, and urethral sphincter dysfunction observed on magnetic resonance imaging (MRI) towards stress urinary incontinence (SUI) after vaginal delivery.

Materials and Methods

Fifty primiparous women after 6 months of delivery (15 with SUI and 35 without) and 35 nulliparous as continent controls underwent MRI at rest and Valsalva maneuver. A published levator ani scoring system was used to characterize morphological changes of LAM. The severity of the injury was divided into three categories as none, minor, and major. A series of common parameters including levator plate angle, iliococcygeal angle, and levator hiatus were used to describe the functional conditions of LAM. Urethral mobility was defined based on the rotation of the urethra between Valsalva and rest status. Vesical neck movement was evaluated by its distance to the pubococcygeal line. Urethral sphincter dysfunction was defined as the widening of the proximal urethra and/or funneling at the urethrovesical junction during Valsalva.

Results

Primiparous incontinent (PI) women had additional major levator ani defects (33.3% vs. 17.1%) while less minor defects (0.7% vs. 31.4%) than primiparous continent (PC) women. Vesical neck downward movement in PI women was more obvious than PC women (28.5 mm vs. 24.2 mm, p = 0.006). Urethral mobility was more active in primiparous women than in nulliparous continent controls (57.4 vs. 52.4), whereas no difference was observed on urethral mobility in the primiparous group (p = 0.25). Urethral sphincter dysfunction and funneling were present in 80% of PI women versus 22.9% in PC women (p < 0.001).

Conclusion

The MRI findings revealed that de novo SUI was associated with major LAM injury, vesical neck downward movement as well as urethral sphincter dysfunction. Vesical neck funneling on sagittal images can be treated as a valuable predictor for SUI. The intervention for the PI should focus on the elevation of vesical neck, rehabilitation of LAM as well as recovery of the urethral sphincter muscle.

The Role of Pelvic Floor Muscle Training in the Conservative and Surgical Management of Female Stress Urinary Incontinence: Does the Strength of the Pelvic Floor Muscles Matter?

The purpose of this review is to provide an in-depth overview of the role of pelvic floor muscle (PFM) training in the management of stress urinary incontinence (SUI). The definition, epidemiology, and pathogenesis of SUI are described. We review the anatomy of the PFM and the importance of PFM strength in maintaining urinary continence and establishing normal voiding function. A brief description of the surgical options currently available for SUI and the existing data regarding the role of perioperative PFM training for SUI are included. Critical research questions to better evaluate and assess PFM training during the perioperative period are proposed. Promising novel approaches in the treatment of SUI are also presented. This review is useful for physiatrists, urogynecologists, female urologists, and nurse practitioners who specialize in the management and treatment of women with SUI. LEVEL OF EVIDENCE: IV.

3D MRI Modeling of Thin and Spatially Complex Soft Tissue Structures without Shrinkage: Lamprey Myosepta as an Example

3D imaging techniques enable the nondestructive analysis and modeling of complex structures. Among these, MRI exhibits good soft tissue contrast, but is currently less commonly used for nonclinical research than X-ray CT, even though the latter requires contrast-staining that shrinks and distorts soft tissues. When the objective is the creation of a realistic and complete 3D model of soft tissue structures, MRI data are more demanding to acquire and visualize and require extensive post-processing because they comprise noncubic voxels with dimensions that represent a trade-off between tissue contrast and image resolution. Therefore, thin soft tissue structures with complex spatial configurations are not always visible in a single MRI dataset, so that standard segmentation techniques are not sufficient for their complete visualization. By using the example of the thin and spatially complex connective tissue myosepta in lampreys, we developed a workflow protocol for the selection of the appropriate parameters for the acquisition of MRI data and for the visualization and 3D modeling of soft tissue structures. This protocol includes a novel recursive segmentation technique for supplementing missing data in one dataset with data from another dataset to produce realistic and complete 3D models. Such 3D models are needed for the modeling of dynamic processes, such as the biomechanics of fish locomotion. However, our methodology is applicable to the visualization of any thin soft tissue structures with complex spatial configurations, such as fasciae, aponeuroses, and small blood vessels and nerves, for clinical research and the further exploration of tensegrity. Anat Rec, 301:1745-1763, 2018. © 2018 Wiley Periodicals, Inc.

Establishing the biomechanical properties of the pelvic soft tissues through an inverse finite element analysis using magnetic resonance imaging

The mechanical characteristics of the female pelvic floor are relevant when explaining pelvic dysfunction. The decreased elasticity of the tissue often causes inability to maintain urethral position, also leading to vaginal and rectal descend when coughing or defecating as a response to an increase in the internal abdominal pressure. These conditions can be associated with changes in the mechanical properties of the supportive structures—namely, the pelvic floor muscles—including impairment. In this work, we used an inverse finite element analysis to calculate the material constants for the passive mechanical behavior of the pelvic floor muscles. The numerical model of the pelvic floor muscles and bones was built from magnetic resonance axial images acquired at rest. Muscle deformation, simulating the Valsalva maneuver with a pressure of 4 KPa, was compared with the muscle displacement obtained through additional dynamic magnetic resonance imaging. The difference in displacement was of 0.15 mm in the antero-posterior direction and 3.69 mm in the supero-inferior direction, equating to a percentage error of 7.0% and 16.9%, respectively. We obtained the shortest difference in the displacements using an iterative process that reached the material constants for the Mooney–Rivlin constitutive model ( c10=11.8 KPa and c20=5.53  E−02 KPa). For each iteration, the orthogonal distance between each node from the group of nodes which defined the puborectal muscle in the numerical model versus dynamic magnetic resonance imaging was computed. With the methodology used in this work, it was possible to obtain in vivo biomechanical properties of the pelvic floor muscles for a specific subject using input information acquired non-invasively.

[Imaging for urinary incontinence]

BACKGROUND

Ultrasonography and functional cine magnetic resonance imaging (MRI) are noninvasive and x-ray free tools, which are currently widely used in clinical diagnostics and scientific research of male and female urinary incontinence. The increasing use and improving techniques of modern imaging tools are closely linked to rapid development of minimally invasive surgery in patients with urinary incontinence and insights gained in continence mechanisms.

METHODS

Whereas ultrasonography is a cost-efficient and readily available diagnostic tool for a routine use, the more expensive functional MRI, as a tool with more precise visualization of functional interactions and spatial representation of anatomical structures of the pelvic floor, is suitable for complex diagnostic purposes and scientific research. Both tools are already well established for evaluations of the female pelvic floor. For evaluation of the male pelvic floor, and in particular postprostatectomy incontinence, perineal ultrasonography and functional cine MRI are becoming increasingly evident.

CONCLUSION

Further development of both imaging tools will contribute to new insights into the continence mechanism and improve the techniques of radical prostatectomy and minimally invasive surgery of male and female urinary incontinence in the future.

Modeling the contraction of the pelvic floor muscles

We performed numerical simulation of voluntary contraction of the pelvic floor muscles to evaluate the resulting displacements of the organs and muscles. Structures were segmented in Magnetic Resonance (MR) images. Different material properties and constitutive models were attributed. The Finite Element Method was applied, and displacements were compared with dynamic MRI findings. Numerical simulation showed muscle magnitude displacement ranging from 0 to 7.9 mm, more evident in the posterior area. Accordingly, the anorectum moved more than the uterus and bladder. Dynamic MRI showed less 0.2 mm and 4.1 mm muscle dislocation in the anterior and cranial directions, respectively. Applications of this model include evaluating muscle impairment, subject-specific mesh implant planning, or effectiveness of rehabilitation.

ACR Appropriateness Criteria pelvic floor dysfunction

Pelvic floor dysfunction is a common and potentially complex condition. Imaging can complement physical examination by revealing clinically occult abnormalities and clarifying the nature of the pelvic floor defects present. Imaging can add value in preoperative management for patients with a complex clinical presentation, and in postoperative management of patients suspected to have recurrent pelvic floor dysfunction or a surgical complication. Imaging findings are only clinically relevant if the patient is symptomatic. Several imaging modalities have a potential role in evaluating patients; the choice of modality depends on the patient's symptoms, the clinical information desired, and the usefulness of the test. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions; they are reviewed every 3 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals, and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

Brain-derived neurotrophic factor in urinary continence and incontinence

Urinary incontinence adversely affects quality of life and results in an increased financial burden for the elderly. Accumulating evidence suggests a connection between neurotrophins, such as brain-derived neurotrophic factor (BDNF), and lower urinary tract function, particularly with regard to normal physiological function and the pathophysiological mechanisms of stress urinary incontinence (SUI) and bladder pain syndrome/interstitial cystitis (BPS/IC). The interaction between BDNF and glutamate receptors affects both bladder and external urethral sphincter function during micturition. Clinical findings indicate reduced BDNF levels in antepartum and postpartum women, potentially correlating with postpartum SUI. Experiments with animal models demonstrate that BDNF is decreased after simulated childbirth injury, thereby impeding the recovery of injured nerves and the restoration of continence. Treatment with exogenous BDNF facilitates neural recovery and the restoration of continence. Serotonin and noradrenaline reuptake inhibitors, used to treat both depression and SUI, result in enhanced BDNF levels. Understanding the neurophysiological roles of BDNF in maintaining normal urinary function and in the pathogenesis of SUI and BPS/IC could lead to future therapies based on these mechanisms.

Magnetic resonance imaging of pelvic floor disorders

Physical examination alone is often inadequate for evaluation of pelvic floor dysfunction. Magnetic resonance imaging (MRI) is a robust modality that can provide high-quality anatomic and functional evaluation of the pelvic floor. Although lack of standardized technique and radiologist inexperience may be relative deterrents in universal acceptance of pelvic floor MRI, the role of MRI is increasing as it is technically feasible on most magnets and offers some advantages over the traditional fluoroscopic defecography. This review focuses on the technical and interpretational aspects of anatomic and functional pelvic floor MRI.

MRI role in morphological and functional assessment of the levator ani muscle: use in patients affected by stress urinary incontinence (SUI) before and after pelvic floor rehabilitation

OBJECTIVE

Pelvic floor dysfunctions affect a very high proportion of female population. Magnetic resonance imaging is the only technique able to provide a multiplanar overview of pelvic organs and muscles without the use of ionizing radiation. The aim of our prospective study is to objectively evaluate the effectiveness of perineal re-education applying MR technique.

MATERIALS AND METHODS

22 patients affected by stress urinary incontinence were enrolled in our prospective study. They underwent urogynaecological, urodynamic examinations, and a questionnaire about symptoms (ICIQ-UI) to investigate the degree of their interference with daily activities. Then they underwent a morphological and dynamic MR exam.

RESULTS

The pre-perineal rehabilitation MR examinations showed an asymmetry of the levator ani muscle in 87% of patients; the remaining 13% showed a muscular bilateral volume reduction. In the group with unilateral defect, the muscle total volume had values between 15 and 21 cm3. Its overall volume was 34.2% smaller on the defective side (9.28±0.26 cm3) compared to the normal side (12.64±12.31 cm3, P<0.001). In patients with a bilateral impairment, the muscle was replaced by fibro-fatty tissue, without a significant asymmetry between the two sides. The post-perineal rehabilitation MR tests showed three different degrees of response to therapy, with a "complete response" found in 67% of patients and no response in 13%.

CONCLUSIONS

MR is an useful tool in the management of patients affected by stress urinary incontinence with indication for perineal rehabilitation. Its objective data allow to distinguish different types of response to therapy and, consequently, different outcomes in terms of additional treatments.

Magnetic resonance imaging of the pelvic floor: from clinical to biomechanical imaging

This article reviews the current role of magnetic resonance imaging in the study of the pelvic floor anatomy and pelvic floor dysfunction. The application of static and dynamic magnetic resonance imaging in the clinical context and for biomechanical simulation modeling is assessed, and the main findings are summarized. Additionally, magnetic resonance-based diffusion tensor imaging is presented as a potential tool to evaluate muscle fiber morphology. In this article, focus is set on pelvic floor muscle damage related to urinary incontinence and pelvic organ prolapse, sometimes as a consequence of vaginal delivery. Modeling applications that evaluate anatomical and physiological properties of pelvic floor are presented to further illustrate their particular characteristics. Finally, finite element method is described as a method for modeling and analyzing pelvic floor structures' biomechanical performance, based on material and behavioral properties of the tissues, and considering pressure loads that mimic real-life conditions such as active contraction or Valsalva maneuver.

Stress incontinence in the era of regenerative medicine: reviewing the importance of the pudendal nerve

PURPOSE

Regenerative medicine will likely facilitate improved stress urinary incontinence treatment via the restoration of its neurogenic, myogenic and structural etiologies. Understanding these pathophysiologies and how each can optimally benefit from cellular, molecular and minimally invasive therapies will become necessary. While stem cells in sphincteric deficiency dominate the regenerative urology literature, little has been published on pudendal nerve regeneration or other regenerative targets. We discuss regenerative therapies for pudendal nerve injury in stress urinary incontinence.

MATERIALS AND METHODS

A PubMed® search for pudendal nerve combined individually with regeneration, injury, electrophysiology, measurement and activity produced a combined but nonindependent 621 results. English language articles were reviewed by title for relevance, which identified a combined but nonindependent 68 articles. A subsequent Google Scholar™ search and a review of the references of the articles obtained aided in broadening the discussion.

RESULTS

Electrophysiological studies have associated pudendal nerve dysfunction with stress urinary incontinence clinically and assessed pudendal nerve regeneration functionally, while animal models have provided physiological insight. Stem cell treatment has improved continence clinically, and ex vivo sphincteric bulk and muscle function gains have been noted in the laboratory. Stem cells, neurotrophic factors and electrical stimulation have benefited pudendal nerve regeneration in animal models.

CONCLUSIONS

Most regenerative studies to date have focused on stem cells restoring sphincteric function and bulk but whether a sphincter denervated by pudendal nerve injury will benefit is unclear. Pudendal nerve regeneration appears possible through minimally invasive therapies that show significant clinical potential. Treating poor central control and coordination of the neuromuscular continence mechanism remains another challenge.

Clinical and functional anatomy of the urethral sphincter

Continence and micturition involve urethral closure. Especially, insufficient strength of the pelvic floor muscles including the urethral sphincter muscles causes urinary incontinence (UI). Thus, it is most important to understand the main mechanism causing UI and the relationship of UI with the urethral sphincter. Functionally and anatomically, the urethral sphincter is made up of the internal and the external sphincter. We highlight the basic and clinical anatomy of the internal and the external sphincter and their clinical meaning. Understanding these relationships may provide a novel view in identifying the main mechanism causing UI and surgical techniques for UI.

Risk factors for the development of stress urinary incontinence in women

Large-scale population-based surveys published in the past decade give new insights regarding risk factors for stress urinary incontinence (SUI) in women. Age plays a significant role in the development of all forms of urinary incontinence, but findings regarding the role of hormonal changes are inconsistent. Obesity is an increasingly prevalent health condition that was shown to have detrimental impact on SUI development, while weight reduction was proven to reduce SUI. Other modifiable risk factors, such as diabetes, also are related to SUI. Pregnancy, delivery, and pelvic floor surgery are risk factors discussed in the review. Recent genetic studies identified several genes encoding components of the extracellular matrix, which could be related to a predisposition to SUI. Identifying risk factors for SUI can facilitate prevention strategies in an aim to reduce SUI prevalence among women.

Relationship between Proximal Urethrovaginal Space Thickness and Detrusor Overactivity in Women with Stress Urinary Incontinence

Purpose

Detrusor overactivity (DO) cannot be predicted by clinical symptoms. Although it is possible that DO could be related to anatomical structures, scanty data exist about the relations between DO and anatomical structures. The aim of this study was to investigate anatomical differences in DO by measuring the thickness of the urethrovaginal space (UVS) and the urethral length (UL) in women with stress urinary incontinence (SUI).

Materials and Methods

Prospective data were collected from 72 women with SUI who underwent the midurethral sling operation. The subjects were divided into 2 groups according to the presence of DO by preoperative urodynamic study (UDS). UVS thickness was measured by trans-vaginal ultrasound. UL was measured by using a urethral catheter and a ruler. UVS thickness, UL, Q-tip, and urodynamic parameters, such as maximal urethral closure pressure (MUCP) and Valsalva leak point pressure, were compared between the two groups.

Results

Of 72 women, 23 patients had DO (31.9%). The proximal UVS was significantly thinner (p<0.001) and the MUCP was significantly lower (p=0.008) in women with DO. According to the receiver operating characteristic (ROC) curve based DO prediction, the best cutoff value for UVS thickness was 0.84 cm (area under the ROC curve 0.763).

Conclusions

In this study, the proximal UVS was significantly thinner and the MUCP was significantly lower in patients with DO. A proximal UVS thickness of less than 0.84 cm was shown to be a predictive parameter for the development of DO on preoperative UDS. A large-scale prospective study is needed to validate these results.

Neurogenic aspects of stress urinary incontinence

PURPOSE OF REVIEW

Vaginal childbirth is a significant risk factor for stress urinary incontinence (SUI). Women with SUI demonstrate dysfunction of the pelvic floor and pudendal nerve. Animal models of SUI have been developed to investigate its pathophysiology and for preclinical testing of potential treatments.

RECENT FINDINGS

Vaginal distension, a method of simulating childbirth injury in animals, produces a reliable decrease in leak point pressure (LPP), a measure of urethral resistance to leakage and quantification of SUI severity in animals. In addition to ischemia and direct tissue damage, vaginal distension causes denervation of the external urethral sphincter (EUS). Pudendal nerve crush produces a similar decrease in LPP, whereas combined PNC and vaginal distension injury delays recovery of LPP compared with either single injury alone. Neurophysiologic studies have elucidated the results of each injury and their combination on pudendal nerve and EUS function. Urethrolysis, electrocautery, and pudendal nerve transection produce more durable functional impairment via both structural damage and denervation. Pubourethral ligament injury eliminates the structural support of the urethra, but its neurologic effects are unknown.

SUMMARY

Animal models demonstrate a complex interplay between tissue damage and pudendal nerve dysfunction, and provide insight into the importance of neuroregeneration in the recovery of continence.

Postpartum stress urinary incontinence: lessons from animal models

Postpartum stress urinary incontinence (SUI) is associated with chronic SUI in later life, which is 240% more likely to occur in women who deliver vaginally than those who did not. The etiology of SUI is multifactoral and has been associated with defects in both neuromuscular and structural components of continence. Specifically, clinical studies have demonstrated that pudendal nerve damage occurs during vaginal delivery, supporting the concept that neuromuscular damage to the continence mechanism can result in postpartum SUI. Urethral hypermobility and the loss of pelvic floor support, such as that involved in pelvic organ prolapse, have also been associated with SUI. Animal models provide an opportunity to investigate these injuries, individually and in combination, enabling researchers to gain further insight into their relative contributions to the development of SUI and the effectiveness of potential therapies for it. This article discusses the use of animal models of postpartum SUI in addition to the broad insights into treatment efficacy they provide.

Urethral sphincter morphology and function with and without stress incontinence

PURPOSE

Using magnetic resonance images we analyzed the relationship between urethral sphincter anatomy, urethral function and pelvic floor function.

MATERIALS AND METHODS

A total of 103 women with stress incontinence and 108 asymptomatic continent controls underwent urethral profilometry, urethral axis measurement with a cotton swab, vaginal closure force measurement with an instrumented speculum and magnetic resonance imaging. Striated urogenital sphincter length was determined and its thickness was measured in the proximal sphincter, where its circular shape enables estimation of striated urogenital sphincter area. A length-area index was calculated as a proxy for volume.

RESULTS

The striated urogenital sphincter in women with stress incontinence was 12.5% smaller than that in asymptomatic continent women (mean +/- SD length-area index 766.4 +/- 294.3 vs 876.2 +/- 407.3 mm(3), p = 0.04). The groups did not differ significantly in striated urogenital sphincter length (13.2 +/- 3.4 vs 13.7 +/- 3.9 mm, p = 0.40), thickness (2.83 +/- 0.8 vs 3.11 +/- 1.4 mm, p = 0.09) or area (59.1 +/- 18.4 vs 62.9 +/- 24.7 mm(2), p = 0.24). Striated urogenital sphincter length and area, and the length-area index were associated during voluntary pelvic muscle contraction with more urethral axis elevation and increased vaginal closure force augmentation.

CONCLUSIONS

A smaller striated urogenital sphincter is associated with stress incontinence and poorer pelvic floor muscle function.

Bilateral avulsion of the puborectal muscle: magnetic resonance imaging-based three-dimensional reconstruction and comparison with a model of a healthy nulliparous woman

OBJECTIVES

Obstetric trauma to the puborectal muscle seems to be an important cause of pelvic floor dysfunction in women. Due to the complicated three-dimensional (3D) arrangement of the pelvic structures, two-dimensional images are not sufficient to demonstrate its relationships in a complex fashion. Thus, we aimed to create a 3D computer model to visualize the normal female pelvic floor anatomy and to compare this with the anatomy after bilateral avulsion of the puborectal muscle following delivery.

METHODS

We created two 3D computer models of the female pelvic floor, one of a healthy nulliparous woman and the other of a woman with bilateral puborectal muscle avulsion after vaginal delivery. The data for the models were obtained from magnetic resonance imaging examinations and the following structures were depicted: pelvic bones, puborectal muscle, internal obturator muscle, urethra, urinary bladder, vagina and rectum. The models were compared.

RESULTS

The models allowed us to demonstrate in three dimensions changes in the puborectal muscle after avulsion. Its relations to the bone, internal obturator muscle, perineal membrane and the deep part of the external anal sphincter were modeled and differences from the normal non-injured anatomy were demonstrated. Avulsion altered the support to the whole endopelvic fascia and destabilized both the anterior and the posterior vaginal walls.

CONCLUSIONS

The use of 3D technology including modeling allows for the acquisition of new knowledge and aids in the understanding of both normal and pathological pelvic anatomy.