The anatomy of the perineal membrane: its relationship to injury in childbirth and episiotomy

An International Continence Society (ICS)/ International Urogynecological Association (IUGA) joint report on the terminology for the assessment and management of obstetric pelvic floor disorders

AIMS

The terminology of obstetric pelvic floor disorders should be defined and reported as part of a wider clinically oriented consensus.

METHODS

This Report combines the input of members of two International Organizations, the International Continence Society (ICS) and the International Urogynecological Association (IUGA). The process was supported by external referees. Appropriate clinical categories and a sub-classification were developed to give coding to definitions. An extensive process of 12 main rounds of internal and 2 rounds of external review was involved to exhaustively examine each definition, with decision-making by consensus.

RESULTS

A terminology report for obstetric pelvic floor disorders, encompassing 357 separate definitions, has been developed. It is clinically-based with the most common diagnoses defined. Clarity and user-friendliness have been key aims to make it usable by different specialty groups and disciplines involved in the study and management of pregnancy, childbirth and female pelvic floor disorders. Clinical assessment, investigations, diagnosis, conservative and surgical treatments are major components. Illustrations have been included to supplement and clarify the text. Emerging concepts, in use in the literature and offering further research potential but requiring further validation, have been included as an Appendix. As with similar reports, interval (5-10 year) review is anticipated to maintain relevance of the document and ensure it remains as widely applicable as possible.

CONCLUSION

A consensus-based Terminology Report for obstetric pelvic floor disorders has been produced to support clinical practice and research.

Surgical anatomy of the vaginal introitus

Aim

The vaginal introitus is the entrance to the vagina, encompassing the anterior and posterior vestibules and the perineum. The surgical anatomy of the vaginal introitus, the lowest level of the vagina, has not been subject to a recent comprehensive examination and description. Vaginal introital surgery (perineorrhaphy) should be a key part of surgery for a majority of pelvic organ prolapse.

Methods

Cadaver studies were performed on the anterior and posterior vestibules and the perineum. Histological studies were performed on the excised perineal specimens of a cohort of 50 women undergoing perineorrhaphy. Included are pre‐ and postoperative studies which were performed on 50 women to determine the anatomical and histological changes achieved with a simple (anterior) perineorrhaphy.

Results

The vaginal introitus is equivalent to the Level III section of the vagina, measured posteriorly from the clitoris to the anterior perineum then down the perineum to the anal verge. The anterior and posterior vestibules, with nonkeratinizing epithelium, extend laterally to the keratinized epithelium of the labia minora (Hart's line). The anterior vestibule has six anatomical layers while the posterior vestibule has three. The perineum has an inverse trapezoid shape. Perineorrhaphy specimens were a mean 2.9 cm wide and 1.6 cm deep. They show squamous epithelium with loose underlying connective tissue. There were no important structures seen histologically, for example, ligaments or muscles. Microscopically, only 6 (12%) were completely normal with 44 (88%) showing minor changes including inflammation and scarring. Considerable anatomical benefits were achieved with such a perineorrhaphy including a 27.6% increase in the perineal length and a 30.8% reduction in the genital hiatus.

Conclusion

An understanding of the anatomy and histology of the vaginal introitus can assist with performing a simple and effective perineorrhaphy, the main surgical intervention at the vaginal introitus.

Novel 3D MRI technique to measure perineal membrane structural changes with pregnancy and childbirth: Technique development and measurement feasibility

INTRODUCTION AND HYPOTHESIS

We aimed to develop and validate a new MRI-based perineal membrane reconstruction and morphological measurement technique, and test its feasibility on nulliparous and parous women to determine the effects of pregnancy and childbirth on the perineal membrane.

METHODS

The perineal membrane was traced on high-resolution MRI using 3D Slicer® and analyses performed using Rhinoceros 6.0 SR23®. Validation was done by comparing MRI-based perineal membrane reconstruction to dissection measurements in a cadaver. Feasibility of reconstruction was assessed in the following three groups: nulliparous (NP), primiparous women who underwent cesarean delivery (CD), and primiparous women with vaginal delivery (VD). The following parameters were measured: (1) swinging door angle, (2) bony and (3) soft tissue attachment lengths, (4) separation at perineal body level, (5) surface area, and (6) hiatal area. ANOVA and post-hoc comparisons were performed, and the effect sizes (d) were reported.

RESULTS

Model reconstruction was similar to cadaver dissection findings. Morphological measurements were feasible in all women (NP, n = 10; CS, n = 6; VD, n = 19). Swinging door angle was 13^o greater in CD (p = 0.03; d = 1.15) and 16^o greater in VD (p < 0.001; d = 1.41) compared to NP. VD showed 13% larger separation at the perineal body than NP (p = 0.097, d = 0.84) and 23% larger hiatal area than CD (p = 0.14, d = 0.94).

CONCLUSION

This novel and anatomically validated MRI-based perineal membrane reconstruction technique is feasible. Preliminary findings show that pregnancy and childbirth both influence perineal membrane morphology with VD being associated with the largest swinging door angle and perineal body separation.

Architecture of structures in the urogenital triangle of young adult males; comparison with females

The fibro‐muscular architecture of the urogenital triangle remains contentious. Reasons are small size of the constituting structures and poor visibility with most imaging methods. We reinvestigated the area in serial sections of three males (21–38 years old) of the American and Chinese Visible Human Projects and two 26‐week‐old male fetuses, and compared the findings with earlier observations in females. The mass of the levator ani muscle was approximately twofold smaller and its funnel shape steeper in males than females. In the levator hiatus, a strand of the smooth longitudinal muscle layer of the rectum, the ‘rectourethral (RU) muscle’, extended anteriorly from the anorectal bend to the penile bulb. Fibrous tissue that formed in the inferior reach of the fetal RU muscle identified the location of the developing perineal body (PB) and divided the muscle into posterior ‘rectoperineal’ and anterior ‘deep perineal’ portions. In males, the PB remained small and bipartite, so that the RU muscle presented as an undivided midline structure. The well‐developed female PB, instead, intertwined with the deep perineal muscle and both structures passed the vagina bilaterally to form the perineal membrane in the posterior portion of the urogenital triangle. The urethral rhabdosphincter extended in the anterior portion of the urogenital triangle between the penile bulb inferiorly and the bladder neck superiorly, and consisted of a well‐developed circular ‘membranous’ portion with bilateral posteroinferior ‘wings’ and a thinner ‘prostatic’ portion on the prostate anterior side. In men, muscles occupy the urogenital triangle, but additional tightening of the locally fibrous adipose tissue by the superficial transverse perineal muscle appears necessary to generate functional support in women. An interactive 3D pdf file with these anatomical details (available online) should allow more accurate interpretation of ultrasound, computed tomography and magnetic resonance images.

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.

Three-dimensional transperineal sonographic characteristics of the anal sphincter complex in nulliparous women

OBJECTIVE

To explore the morphological characteristics and normal biometry of the anal sphincter complex in nulliparous Chinese women using three-dimensional (3D) transperineal ultrasound.

METHODS

3D sonographic data from 55 nulliparous Chinese women (aged 19-38 years) who had no pelvic organ prolapse and no symptoms of pelvic floor dysfunction were retrieved from an image dataset and analyzed by offline post-processing. The morphological characteristics of the external and internal anal sphincters, puborectalis muscle and perineal body were assessed in the sagittal, coronal and axial views.

RESULTS

The external anal sphincter had three sonographic components: the circular main body, a subcutaneous part and an extension portion. It was significantly thinner at 12 o'clock than at the 3, 6 and 9 o'clock positions. The internal anal sphincter was seen as dark echolucent strips of equal thickness. In the mid-sagittal view, it started from the anal verge and ended at the anorectal junction. The perineal body was an ovoid structure covering the upper margin of the external sphincter, while the puborectalis muscle was banana-shaped in the sagittal view and was located behind the anorectal junction, extending downward along the inferior margin of the posterior external sphincter extension. Sonographic characteristics of the anal sphincter complex did not vary with age, weight, height or body mass index.

CONCLUSIONS

3D transperineal ultrasound clearly demonstrates the spatial relationships of each component of the anal sphincter complex. This should allow standardized measurement of the complex for investigations of its function.

A method of dissecting the pelvic floor to allow anatomical validation of images of the soft tissues

A method of intact postmortem removal of the pelvic floor for imaging correlation studies, with minimal access disfigurement, is described. This consists of subcutaneous removal of both ischiopubic rami with division of the obturator membrane cranial to the origin of the levator ani muscles. The anatomical relationships of soft tissue surrounding the distal birth canal are thus preserved. The report discusses the need for, constraints on, and limitations of such studies in the unique problems of determining the dynamic anatomical configuration of the soft tissues of the pelvic floor. It illustrates the clinical relevance of initial studies, and reviews the background contributions of members of the group.

Obstetric anal sphincter injury ten years after: subjective and objective long term effects

OBJECTIVE

To establish the long term effects of obstetric anal sphincter rupture.

DESIGN

Prospective observational study.

SETTING

University hospital in Sweden.

POPULATION

Eighty-two women from a prospective study from 1990 to compare anorectal function after third degree tear.

METHODS

Women completed a structured questionnaire, underwent a clinical examination and anorectal manometry, endoanal ultrasound (EAUSG) with perineal body measurement.

MAIN OUTCOME MEASURES

Symptoms of anal incontinence, sexual symptoms, anal manometry scores and evidence of sphincter damage on EAUSG.

RESULTS

Five women had undergone secondary repair and three were lost to follow up. Fifty-one women (80%) completed the questionnaire. Twenty-six out of 46 (57%) of the original study group and 6/28 (20%) of the original controls were examined. Incontinence to flatus and liquid stool was more severe in the study group than in controls. Flatus incontinence was significantly more pronounced among women with subsequent vaginal deliveries. Mean maximal anal squeeze pressures were 69 mmHg in the partial rupture group and 42 mmHg in the complete rupture group (P= 0.04). Study group women with signs of internal sphincter injury reported more pronounced faecal incontinence and had lower anal resting pressures (24 mmHg) than those with intact internal sphincters (40 mmHg) (P= 0.01). Perineal body thickness of less than 10 mm was associated with incontinence for flatus and liquid stools, less lubrication during sex and lower anal squeeze pressures (58 mmHg vs 89 mmHg, P= 0.04).

CONCLUSIONS

Subjective and objective anal function after anal sphincter injury deteriorates further over time and with subsequent vaginal deliveries. Thin perineal body and internal sphincter injury seem to be important for continence and anal pressure.