Morphologies of the interfaces between the levator ani muscle and pelvic viscera, with special reference to muscle insertion into the anorectum in elderly Japanese

Clinical efficacy and pathological outcomes of transanal endoscopic intersphincteric resection for low rectal cancer

BACKGROUND

Transanal endoscopic intersphincteric resection (ISR) surgery currently lacks sufficient clinical research and reporting.

AIM

To investigate the clinical effectiveness of transanal endoscopic ISR, in order to promote the clinical application and development of this technique.

METHODS

This study utilized a retrospective case series design. Clinical and pathological data of patients with lower rectal cancer who underwent transanal endoscopic ISR at the First Affiliated Hospital of Xiamen University between May 2018 and May 2023 were included. All patients underwent transanal endoscopic ISR as the surgical approach. We conducted this study to determine the perioperative recovery status, postoperative complications, and pathological specimen characteristics of this group of patients.

RESULTS

This study included 45 eligible patients, with no perioperative mortalities. The overall incidence of early complications was 22.22%, with a rate of 4.44% for Clavien-Dindo grade ≥ III events. Two patients (4.4%) developed anastomotic leakage after surgery, including one case of grade A and one case of grade B. Postoperative pathological examination confirmed negative circumferential resection margins and distal resection margins in all patients. The mean distance between the tumor lower margin and distal resection margin was found to be 2.30 ± 0.62 cm. The transanal endoscopic ISR procedure consistently yielded high quality pathological specimens.

CONCLUSION

Transanal endoscopic ISR is safe, feasible, and provides a clear anatomical view. It is associated with a low incidence of postoperative complications and favorable pathological outcomes, making it worth further research and application.

Pelvic floor and perineal muscles: a dynamic coordination between skeletal and smooth muscles on pelvic floor stabilization

The purpose of this review is to present our researches on the pelvic outlet muscles, including the pelvic floor and perineal muscles, which are responsible for urinary function, defecation, sexual function, and core stability, and to discuss the insights into the mechanism of pelvic floor stabilization based on the findings. Our studies are conducted using a combination of macroscopic examination, immunohistological analysis, 3D reconstruction, and imaging. Unlike most previous reports, this article describes not only on skeletal muscle but also on smooth muscle structures in the pelvic floor and perineum to encourage new understanding. The skeletal muscles of the pelvic outlet are continuous, which means that they share muscle bundles. They form three muscle slings that pass anterior and posterior to the anal canal, thus serving as the foundation of pelvic floor support. The smooth muscle of the pelvic outlet, in addition to forming the walls of the viscera, also extends in three dimensions. This continuous smooth muscle occupies the central region of the pelvic floor and perineum, thus revising the conventional understanding of the perineal body. At the interface between the levator ani and pelvic viscera, smooth muscle forms characteristic structures that transfer the lifting power of the levator ani to the pelvic viscera. The findings suggest new concepts of pelvic floor stabilization mechanisms, such as dynamic coordination between skeletal and smooth muscles. These two types of muscles possibly coordinate the direction and force of muscle contraction with each other.

A missing distal complex of the external and internal anal sphincters: a macroscopic and histologic study using Japanese and German elderly cadavers

The lower margin of the internal anal sphincter (IAS) is considered to lie on a J-shaped, subcutaneous part (SCP) of the external anal sphincter (EAS). The lower IAS is united with the J-shaped SCP to form a smooth-striated muscle complex. In the first part of this study, we ensured the presence of the J-shaped EAS in the lateral wall of the anal canal from 12 near-term fetuses. Second, in the lateral anal wall, the examination of the longitudinal section from 20 male and 24 female Japanese cadavers (72-95 years-old) demonstrated that the J-shaped EAS was lost in 15 (34%) due to the very small SCP. Third, we demonstrated that the J-shaped EAS was restricted in the latera anal wall using longitudinal histological sections of the anal canal from 11 male Japanese cadavers (75-89 years-old). Therefore, a site-dependent difference in the IAS-EAS configuration was evident. Finally, we compared a frequency of the lost J-shape between human populations using 10 mm-thick frontal slices from 36 Japanese and 28 German cadavers. The two groups of cadavers were compatible in age (a 0.2-years' difference in males). The macroscopic observations revealed that the J-shaped EAS was absent from 13 (36%) Japanese and six (20%) German specimens, suggesting that the SCP degeneration occurred more frequent in elderly Japanese than elderly German individuals (p < 0.05). The distal IAS-EAS complex seemed to push residual feces out of the anal canal at a transient phase from evacuation to closure. The absence might be the first sigh of anal dysfunction.

Spatial distribution of smooth muscle tissue in the female pelvic floor and surrounding the urethra and vagina

Data regarding urethral supporting structures are insufficient for understanding the mechanism of stress urinary incontinence. Whether smooth muscle fibers contribute to urethral support and pelvic floor support structures is unclear. This study aimed to clarify the histological structures and spatial distributions of smooth muscle tissues surrounding the urethra and vagina. Using cadaveric specimens, macroscopic anatomical and histological evaluations were conducted. Six female cadavers were used for macroscopic observations. Ten female cadavers were used for histological observations. Three pelvises were cut in a plane vertical to the urethra, and the other pelvises were cut in a plane parallel to the urethra and vagina to observe tissues surrounding the urethra and vagina. The major tissue component around the proper muscle layer of the urethra was smooth muscle tissue, which mediated among the urethra, pubis, and levator ani. Smooth muscle tissues laterally extended the smooth muscle fibers, both superiorly and inferiorly toward the levator ani, with a few fibers inserted in the levator ani. Smooth muscle was found between the urethral walls and pubic bones. Smooth muscle may contribute to the mechanism of pelvic floor support.

Smooth muscle of the male pelvic floor: An anatomic study

Knowledge of the anatomy of the male pelvic floor is important to avoid damaging the pelvic floor muscles during surgery. We set out to explore the structure and innervation of the smooth muscle (SM) of the whole pelvic floor using male fetuses. We removed en-bloc the entire pelvis of three male fetuses. The specimens were serially sectioned before being stained with Masson's trichrome and hematoxylin and eosin, and immunostained for SMs, and somatic, adrenergic, sensory and nitrergic nerve fibers. Slides were digitized for three-dimensional reconstruction. We individualized a middle compartment that contains SM cells. This compartment is in close relation with the levator ani muscle (LAM), rectum, and urethra. We describe a posterior part of the middle compartment posterior to the rectal wall and an anterior part anterior to the rectal wall. The anterior part is split into (1) a centro-levator area of SM cells localized between the right and left LAM, (2) an endo-levator area that upholsters the internal aspect of the LAM, and (3) an infra-levator area below the LAM. All these areas are innervated by autonomic nerves coming from the inferior hypogastric plexus. The core and the infra-levator area receive the cavernous nerve and nerves supplying the urethra. We thus demonstrate that these muscular structures are smooth and under autonomic influence. These findings are relevant for the pelvic surgeon, and especially the urologist, during radical prostatectomy, abdominoperineal resection and intersphincteric resection. Clin. Anat., 2019. © 2019 Wiley Periodicals, Inc.

Precise Three-Dimensional Morphology of the Male Anterior Anorectum Reconstructed From Large Serial Histologic Sections: A Cadaveric Study

BACKGROUND

Deep anatomic knowledge of the male anterior anorectum is important to avoid urethral injury and rectal perforation in intersphincteric resection or abdominoperineal resection for very low rectal cancer. However, its structure is difficult to understand, because the anorectum, muscles, and urogenital organs are complicatedly and 3-dimensionally arranged.

OBJECTIVE

The purpose of this study was to revisit the anatomic information of the male anterior anorectum for intersphincteric resection and abdominoperineal resection with a focus on the spatial muscular morphology.

DESIGN

This was a descriptive cadaveric study.

SETTINGS

The study was conducted at Ehime and Kyoto universities.

PATIENTS

Tissue specimens from 9 male cadavers were included.

MAIN OUTCOME MEASURES

Specimens around the anterior anorectum were serially sectioned in the horizontal, sagittal, or frontal plane; large semiserial histologic sections were created at 250-μm intervals. The series were stained with Elastica van Gieson, and some sections from the series were studied by immunohistochemistry to detect smooth and striated muscles. Two series were digitalized and reconstructed 3-dimensionally.

RESULTS

Two regions without a clear anatomic border were elucidated: 1) the anterior region of the external anal sphincter, where the external anal sphincter, bulbospongiosus muscle, and superficial transverse perineal muscle were intertwined; and 2) the rectourethralis muscle, where the smooth muscle of the longitudinal muscle continuously extended to the posteroinferior area of the urethra, which became closest to the anorectum at the prostatic apex level. A tight connection between the striated and smooth muscles was identified at the anterior part of the upper external anal sphincter and anterolateral part of the puborectalis muscle level.

LIMITATIONS

This study involved a small sample size of elderly cadavers.

CONCLUSIONS

This study clarified the precise spatial relationship between smooth and striated muscles. The detailed anatomic findings will contribute more accurate step-by-step anterior dissection in intersphincteric resection and abdominoperineal resection, especially with the transanal approach, which can magnify the muscle fiber direction and contraction of striated muscle by electrostimulation. MORFOLOGÍA TRIDIMENSIONAL PRECISA DEL ANORRECTO ANTERIOR MASCULINO RECONSTRUIDO A TRAVÉS DE SECCIONES MAYORES HISTOLÓGICAS EN SERIE: UN ESTUDIO CADAVÉRICO: El conocimiento anatómico amplio del anorrecto anterior masculino es importante para evitar lesiones de uretra y perforación de recto en la resección interesfinterica o la resección abdominoperineal para cáncer de recto bajo. Sin embargo, su estructura es difícil de entender porque el anorrecto, los músculos y los órganos urogenitales están aliñados en forma complexa tridimensional.

OBJETIVO

Revisar de nuevo el conocimiento anatómico del anorrecto anterior masculino relevante a la resección interesfinterica y la resección abdominoperineal con un enfoque en la morfología muscular espacial. DISEÑO:: Estudio descriptivo cadavérico.

ENTORNO

Ehime y la Universidad de Kyoto.

SUJETOS

Tejido especímenes de nueve cadáveres masculinos. PUNTOS FINALES DE VALORACIÓN:: Las muestras alrededor del anorrecto anterior se seccionaron en serie en planos horizontal, sagital y coronal. Se crearon mayores secciones histológicas en serie a intervalos de 250 μm. Los especímenes fueron teñidos con Elástica van Gieson, y algunas secciones de la serie se estudiaron mediante inmunohistoquímica para detectar músculos lisos y estriados. Dos series fueron digitalizadas y reconstruidas tridimensionalmente.

RESULTADOS

Se demostraron dos regiones sin un borde anatómico definido: (i) la región anterior del esfínter anal externo, donde se entrelazaron el esfínter anal externo, el músculo bulbospongoso y el músculo perineal transverso superficial; y (ii) músculo rectouretral, donde el músculo liso del músculo longitudinal se extiende continuamente a la zona posteroinferior de la uretra, que se acerca más al anorrecto a nivel del ápice prostático. La conexión estrecha entre los músculos estriados y lisos se identificó en la parte anterior del esfínter anal externo superior y la parte anterolateral del nivel del músculo puborrectal. LIMITACIÓN:: Este estudio incluyó una muestra pequeña de cadáveres ancianos. CONCLUSIÓN:: Este estudio aclaró la relación espacial precisa entre los músculos lisos y estriados. Los hallazgos anatómicos detallados ayudarán para una disección anterior paso a paso más precisa en la resección interesfintérica y la resección abdominoperineal, especialmente con el abordaje transanal, que puede magnificar la dirección de las fibras musculares y la contracción del músculo estriado utilizando electroestimulación.

Topographic Anatomy of the Anal Sphincter Complex and Levator Ani Muscle as It Relates to Intersphincteric Resection for Very Low Rectal Disease

BACKGROUND

Intersphincteric resection has become a widely used treatment for patients with rectal cancer. However, the detailed anatomy of the anal canal related to this procedure has remained unclear.

OBJECTIVE

The purpose of this study was to clarify the detailed anatomy of the anal canal.

DESIGN

This is a descriptive study.

SETTINGS

Histologic evaluations of paraffin-embedded tissue specimens were conducted at a tertiary referral hospital.

PATIENTS

Tissue specimens were obtained from cadavers of 5 adults and from 13 patients who underwent abdominoperineal resection for rectal cancer.

MAIN OUTCOME MEASURES

Sagittal sections from 9 circumferential portions of the cadaveric anal canal (histologic staining) and 3 circumferential portions from patients were studied (immunohistochemistry for smooth and skeletal muscle fibers).

RESULTS

Longitudinal fibers between the internal and external anal sphincters consisted primarily of smooth muscle fibers that continued from the longitudinal muscle of the rectum. The levator ani muscle attached directly to the lateral surface of the longitudinal smooth muscle of the rectum. The length of the attachment was longer in the anterolateral portion and shorter in the posterior portion of the anal canal. In the lateral and posterior portions, the levator ani muscle partially overlapped the external anal sphincter; however, there was less overlap in the anterolateral portion. In the posterior portion, thick smooth muscle was present on the surface of the levator ani muscle and it continued to the longitudinal muscle of the rectum.

LIMITATIONS

We observed only limited portions in some surgical specimens because of obstruction by tumors.

CONCLUSIONS

The levator ani muscle attaches directly to the longitudinal muscle of the rectum. The spatial relationship between the smooth and skeletal muscles differed in different portions of the anal canal. For intersphincteric resection, dissection must be performed between the longitudinal muscle of the rectum and the levator ani muscle/external anal sphincter, and the appropriate surgical lines must be selected based on the specific structural characteristics of each portion.

Fetal growth of the anal sinus and sphincters, especially in relation to anal anomalies

PURPOSE AND METHODS

The anal sinuses, small furrows above the pectinate line, sometimes form perianal abscesses in adults. We examined the pattern of fetal growth of the anal sinus and sphincters using 22 mid-term (8-18 weeks) and 6 late-stage (30-38 weeks) fetuses.

RESULTS

In mid-term fetuses, the external and internal sphincters gradually increased in thickness, depending on specimen size (from 0.2 to 1.5 mm), whereas the anteroposterior diameter of the anal canal at the epithelial junction was relatively stable (0.5-1.0 mm) irrespective of specimen size. Anal canal diameter increased less than twofold between mid-term and late-stage fetuses, from 0.5-1.0 to almost 2 mm, whereas sphincter thickness increased over tenfold, from 0.2-1.5 to almost 3.5 mm. The anal sinus often showed balloon-like enlargement when the sphincter muscle bundles were tightly packed in mid-term, but not in late-stage fetuses.

CONCLUSIONS

Large concentric mechanical stress from the sphincters in late-stage fetuses apparently prevented the anal sinus from expanding in a balloon-like manner. Conversely, to avoid anal stenosis, the growing sinuses maintained a luminal space of the anal canal in response to stress from rapidly growing sphincters. The inferiorly extending sinus usually provided temporal double canals separated by a thick column. In the presence of double lumens, anal canal duplication is likely to develop without any abnormalities of the anal epithelium and sphincters.

The anococcygeal ligaments: Cadaveric study with application to our understanding of incontinence in the elderly

The term "anococcygeal ligament (ACL)" has been used to refer to two distinct structures: a superficial fibrous band originating from the myosepta of the external anal sphincter (EAS) and running upwards to the coccyx (the superficial ACL); and a deep fibrous band originating from the periosteum of the coccyx, merging with the thick presacral fascia and attaching to the superior end of the EAS (the deep ACL). In the present work, elastic fiber histology and muscle immunohistochemistry of sagittal sections obtained from 15 donated elderly male cadavers showed that superficial ACL, corresponding to a superficial fascia or skin ligament, was composed of very tortuous elastic fibers, with a fine elastic fiber mesh at their coccygeal attachment; whereas the deep ACL was composed of almost straight collagen and elastic fibers, intermingled with the coccygeal periosteum. Due to the weak insertion into the coccyx and the wavy course, the superficial ACL is unlikely to provide, even in association with contraction of the longitudinal anal muscle, a stable mechanical support to maintain the configuration of the EAS. Being similar to the suspensory ligament of breast, tissue repair of the skin ligament would not have a mechanical role. In contrast, the deep ACL, in association with the thick presacral fascia, likely plays a role in maintaining a suitable positioning of the anorectum to the coccyx. However, their relative lack of smooth muscles compared with rich elastic fibers indicates that both ACLs may become permanently overextended under conditions of long-term mechanical stress.

Lack of striated muscle fibers in the longitudinal anal muscle of elderly Japanese: a histological study using cadaveric specimens

PURPOSE AND METHODS

The aim of this study is to investigate variations in the longitudinal anal muscle (LAM), especially in the meeting pattern between the levator ani and rectum at the origin of the LAM. We examined the histology of the anal canal and the lower rectum of 50 cadavers (25 males, 25 females) of elderly Japanese individuals with the aid of immunohistochemistry.

RESULTS

We observed two patterns in the meeting site between the levator ani and the rectum. In type 1, observed in 26 specimens, the smooth muscle-rich fascia lining the internal or medial aspect of the levator ani (i.e., the fascia pelvis parietalis or endopelvic fascia) was connected to the external muscle layer. In type 2, observed in 24 specimens, multiple intramuscular septa of the levator ani were attached to a smooth muscle mass, with the latter joining the external smooth muscle layer of the rectum. However, 21 specimens (6 type 1 and 15 type 2) carried few smooth muscles at the meeting site. We did not find any striated muscle in the LAM, although this might have been the result of age-associated degeneration. Thus, active traction of the pelvic viscera by the LAM seemed unlikely in elderly Japanese.

CONCLUSIONS

Rather than playing an active role, as suggested by the integral pelvic floor theory, the LAM seemed to be an elastic skeleton that maintains the shape of the anal canal.

The urethral rhabdosphincter, levator ani muscle, and perineal membrane: a review

Detailed knowledge of the anatomy of the rhabdosphincter and adjacent tissues is mandatory during urologic surgery to ensure reliable oncologic and functional outcomes. To characterize the levator ani (LA) function for the urethral sphincter, we described connective tissue morphology between the LA and urethral rhabdosphincter. The interface tissue between the LA and rhabdosphincter area in males contained abundant irregularly arrayed elastic fibers and smooth muscles. The male rhabdosphincter was positioned alongside the LA to divide the elevation force and not in-series along the axis of LA contraction. The male perineal membrane was thin but solid and extends along the inferior margin or bottom of the rhabdosphincter area. In contrast, the female rhabdosphincter, including the compressor urethrae and urethrovaginal sphincter muscles, was embedded in the elastic fiber mesh that is continuous with the thick, multilaminar perineal membrane. The inferomedial edge of the female LA was attached to the upper surface of the perineal membrane and not directly attached to the rhabdosphincter. We presented new diagrams showing the gender differences in topographical anatomy of the LA and rhabdosphincter.

Nerves and fasciae in and around the paracolpium or paravaginal tissue: an immunohistochemical study using elderly donated cadavers

The paracolpium or paravaginal tissue is surrounded by the vaginal wall, the pubocervical fascia and the rectovaginal septum (Denonvilliers' fascia). To clarify the configuration of nerves and fasciae in and around the paracolpium, we examined histological sections of 10 elderly cadavers. The paracolpium contained the distal part of the pelvic autonomic nerve plexus and its branches: the cavernous nerve, the nerves to the urethra and the nerves to the internal anal sphincter (NIAS). The NIAS ran postero-inferiorly along the superior fascia of the levator ani muscle to reach the longitudinal muscle layer of the rectum. In two nulliparous and one multiparous women, the pubocervical fascia and the rectovaginal septum were distinct and connected with the superior fascia of the levator at the tendinous arch of the pelvic fasciae. In these three cadavers, the pelvic plexus and its distal branches were distributed almost evenly in the paracolpium and sandwiched by the pubocervical and Denonvilliers' fasciae. By contrast, in five multiparous women, these nerves were divided into the anterosuperior group (bladder detrusor nerves) and the postero-inferior group (NIAS, cavernous and urethral nerves) by the well-developed venous plexus in combination with the fragmented or unclear fasciae. Although the small number of specimens was a major limitation of this study, we hypothesized that, in combination with destruction of the basic fascial architecture due to vaginal delivery and aging, the pelvic plexus is likely to change from a sheet-like configuration to several bundles.

Female longitudinal anal muscles or conjoint longitudinal coats extend into the subcutaneous tissue along the vaginal vestibule: a histological study using human fetuses

PURPOSE

It is still unclear whether the longitudinal anal muscles or conjoint longitudinal coats (CLCs) are attached to the vagina, although such an attachment, if present, would appear to make an important contribution to the integrated supportive system of the female pelvic floor.

MATERIALS AND METHODS

Using immunohistochemistry for smooth muscle actin, we examined semiserial frontal sections of 1) eleven female late-stage fetuses at 28-37 weeks of gestation, 2) two female middle-stage fetus (2 specimens at 13 weeks), and, 3) six male fetuses at 12 and 37 weeks as a comparison of the morphology.

RESULTS

In late-stage female fetuses, the CLCs consistently (11/11) extended into the subcutaneous tissue along the vaginal vestibule on the anterior side of the external anal sphincter. Lateral to the CLCs, the external anal sphincter also extended anteriorly toward the vaginal side walls. The anterior part of the CLCs originated from the perimysium of the levator ani muscle without any contribution of the rectal longitudinal muscle layer. However, in 2 female middle-stage fetuses, smooth muscles along the vestibulum extended superiorly toward the levetor ani sling. In male fetuses, the CLCs were separated from another subcutaneous smooth muscle along the scrotal raphe (posterior parts of the dartos layer) by fatty tissue.

CONCLUSION

In terms of topographical anatomy, the female anterior CLCs are likely to correspond to the lateral extension of the perineal body (a bulky subcutaneous smooth muscle mass present in adult women), supporting the vaginal vestibule by transmission of force from the levator ani.

Nerves in the intersphincteric space of the human anal canal with special reference to their continuation to the enteric nerve plexus of the rectum

In the intersphincteric space of the anal canal, nerves are thought to "change" from autonomic to somatic at the level of the squamous-columnar epithelial junction of the anal canal. To compare the nerve configuration in the intersphincteric space with the configuration in adjacent areas of the human rectum, we immunohistochemically assessed tissue samples from 12 donated cadavers, using antibodies to S100, neuronal nitric oxide synthase (nNOS), and tyrosine hydroxylase (TH). Antibody to S100 revealed a clear difference in intramuscular nerve distribution patterns between the circular and longitudinal muscle layers of the most inferior part of the rectum, with the former having a plexus-like configuration, while the latter contained short, longitudinally running nerves. Most of the intramural ganglion cells in the anal canal were restricted to above the epithelial junction, but some were located just below that level. Near or at the level of the epithelial junction, the nerves along the rectal adventitia and Auerbach's nerve plexus joined to form intersphincteric nerves, with all these nerves containing both nNOS-positive parasympathetic and TH-positive sympathetic nerve fibers. Thus, it was histologically difficult to distinguish somatic intersphincteric nerves from the autonomic Auerbach's plexus. In the intersphincteric space, the autonomic nerve elements with intrapelvic courses seemed to "borrow" a nerve pathway in the peripheral branches of the pudendal nerve. Injury to the intersphincteric nerve during surgery may result in loss of innervation in the major part of the internal anal sphincter.

Anococcygeal raphe revisited: a histological study using mid-term human fetuses and elderly cadavers

PURPOSE

We recently demonstrated the morphology of the anococcygeal ligament. As the anococcygeal ligament and raphe are often confused, the concept of the anococcygeal raphe needs to be re-examined from the perspective of fetal development, as well as in terms of adult morphology.

MATERIALS AND METHODS

We examined the horizontal sections of 15 fetuses as well as adult histology. From cadavers, we obtained an almost cubic tissue mass containing the dorsal wall of the anorectum, the coccyx and the covering skin. Most sections were stained with hematoxylin and eosin or Masson-trichrome solution.

RESULTS

The adult ligament contained both smooth and striated muscle fibers. A similar band-like structure was seen in fetuses, containing: 1) smooth muscle fibers originating from the longitudinal muscle coat of the anal canal and 2) striated muscle fibers from the external anal sphincter (EAS). However, in fetuses, the levator ani muscle did not attach to either the band or the coccyx. Along and around the anococcygeal ligament, we did not find any aponeurotic tissue with transversely oriented fibers connecting bilateral levator ani slings. Instead, in adults, a fibrous tissue mass was located at a gap between bilateral levator ani slings; this site corresponded to the dorsal side of the ligament and the EAS in the immediately deep side of the natal skin cleft.

CONCLUSION

We hypothesize that a classically described raphe corresponds to the specific subcutaneous tissue on the superficial or dorsal side of the anococcygeal ligament.

Reappraisal of intergender differences in the urethral striated sphincter explains why a completely circular arrangement is difficult in females: a histological study using human fetuses

To investigate why the development of a completely circular striated sphincter is so rare, we examined histological sections of 11 female and 11 male mid-term human fetuses. In male fetuses, the striated muscle initially extended in the frontal, rather than in the horizontal plane. However, a knee-like portion was absent in the female fetal urethra because, on the inferior side of the vaginal end, a wide groove for the future vestibule opened inferiorly. Accordingly, it was difficult for the developing striated muscle to surround the groove, even though there was not a great difference in width or thickness between the female vestibule and the male urethra. The development of a completely circular striated sphincter seems to be impossible in females because of interruption of the frontal plane by the groove-like vestibule. However, we cannot rule out the possibility that before descent of the vagina, the urethral striated muscle extends posteriorly.

Intergender differences in histological architecture of the fascia pelvis parietalis: a cadaveric study

The fascia pelvis parietalis (FPP) or endopelvic fascia is a well-known structure, but few studies described the detailed histological architecture, including the composite fiber directions. We hypothesized a gender-specific fiber architecture corresponding to the functional demand. For the first step to examine this hypothesis, we investigated specimens from 27 adult cadavers (10 males and 17 females) and 11 midterm fetuses (five males and six females) using immunohistochemistry and aldehyde-fuchsin staining. The adult female FPP was a solid, thick monolayered structure that was reinforced by abundant elastic fibers running across the striated muscle fibers, but it contained little or no smooth muscles (SM). In contrast, the male FPP was multilayered with abundant SM. In midterm fetuses, SM originated from the inferior part of the bladder and extended inferiorly along the gender-specific courses. Thus, we found a clear intergender difference in FPP architecture. However, the functional significance remained unknown because the basic architecture was common between nulliparous and multiparous women. Rather than for meeting the likely mechanical demands of pregnancy and vaginal delivery, the intergender difference of the FPP seemed to result from differences in the amount and migration course of bladder-derived SM as well as in hormonal background.

Development of the external anal sphincter with special reference to intergender difference: observations of mid-term fetuses (15-30 weeks of gestation)

To investigate intergender differences in muscle cleavage and joining during development of the external anal sphincter (EAS), we examined semiserial sections of 16 fetuses between 15 and 30 weeks of gestation (6 males and 10 females). The subcutaneous part of the EAS (EASsc) developed along the male perineal raphe and extended posteriorly. Thus, the male EAS was characterized by anterior protrusion of the subcutaneous muscle, in contrast to the almost circular female EAS. In both genders, the bulbospongiosus anlage (or the levator ani anlage) issued muscle fibers to form the superficial (or deep) part of the EAS. The EASsc communicated with the superficial part in males, whereas the female bulbospongiosus tended to communicate with the levator ani rather than the EAS. In both genders, the longitudinal muscle bundle(s) of the anorectum contributed to perineal body formation. However, the male perineal body also had a thick fascia between the rhabdosphincter and the levator. The bulbospongiosus seems to play a critical role in forming the EAS. A strict intergender difference in subcutaneous muscle development is evident along the perineal raphe, as the raphe is not evident in females. These results help to explain variations in the EAS, including anal malformations.

Surgical anatomy of intrapelvic fasciae and vesico-uterine ligament in nerve-sparing radical hysterectomy with fresh cadaver dissections

Radical hysterectomy has been performed for invasive cervical cancer, and autonomic nerve-sparing procedures have been developed to preserve bladder function. To perform and improve the nerve-sparing radical hysterectomy, it is important to understand anatomy of the intra pelvic fasciae, specially vesico-uterine ligament (VUL), because most of injuries to the nerves occurred during incision of the VUL in radical hysterectomy procedures. The objectives of the present study were to provide histological understanding of major structures found in nerve-sparing radical hysterectomy. Serial macroscopic slices (15-20 mm thick) from five female pelves were trimmed and prepared for paraffin-embedded histology. We noted an anatomical entity as "the visceroparietal fascial bridge", which corresponds with the macroscopically identified arcus tendineus fasciae pelvis. A histologically identifiable neurovascular pedicle to the bladder neck corresponded with the deep portion of VUL. These findings could help better preservation of autonomic nerves during radical hysterectomy and improve patient's quality of life after the operation. Translation of surgical anatomy into anatomic terminology enables us to have fruitful discussions with persuasive power by excluding any bias from individual surgeons.

A histotopographic study of the perineal body in elderly women: the surgical applicability of novel histological findings

Female perineal structures located around the perineal body were histologically examined using semiserial sections obtained from 15 elderly female cadavers. The smooth muscle content of the perineal body was greater in multiparous women. The connective tissue of the perineal body extended inferolaterally and provided a fibromuscular mass that was 10-30 mm long mediolaterally and 3-15 mm long superoinferiorly. The lateral extension (LEX) of the perineal body occupies a space that is surrounded by the vestibular bulb, internal anal sphincter, and levator ani slings. The LEX did not directly connect to the ischiopubic bony rami but did connect indirectly via the vestibular bulb and ischiocavernosus. Thus, the LEX appears to play a critical role for maintaining the topographical relationship between the vagina and the rectum. The surgical approximation of bilateral LEX instead of levator ani may be of key importance when doing a perineorrhaphy. As pudendal nerve branches run along the inferior margin of the LEX, a mediolateral episiotomy may not be the best option.

Rectourethralis muscle and pitfalls of anterior perineal dissection in abdominoperineal resection and intersphincteric resection for rectal cancer

When performing nerve-sparing abdominoperitoneal resection or intersphincteric resection of lower rectal cancer, difficulty is sometimes encountered during dissection, separation and treatment in the area anterior to the anorectum passing through the levator hiatus between the bilateral levator ani slings owing to missing the surgical plane or venous bleeding. The rectourethralis muscle, which is a mass of smooth muscle, occupies the levator hiatus. The present histological study using nine male cadaveric specimens demonstrated that: (i) the external anal sphincter is likely to be tightly connected to the rectourethralis muscle; (ii) the rectal muscularis propria communicates with the rectourethralis muscle; (iii) the anorectal veins take a tortuous course across the rectourethralis muscle; (iv) Denonvilliers' fascia ends at the rectourethralis muscle; and (v) the rectourethralis muscle provides posterior attachment for the rhabdosphincter. Moreover, the cavernous nerve has been reported to penetrate the rectourethralis muscle. Therefore, careful treatment of the muscle seems to be necessary to avoid male sexual dysfunction. Owing to muscle fiber communications between the rectal muscularis propria and the rectourethralis muscle, and the fact that Denonvilliers' fascia terminates in the rectourethralis muscle, the surgical plane would tend to deeply penetrate the muscle mass. However, mass ligation of the anterior tissues for control of venous bleeding should be avoided. When the tumor is non-anterior, an abdominal surgical plane behind Denonvilliers' fascia is recommended to avoid excess invasion into the rectourethralis muscle.

Histological features of the rectovaginal septum in elderly women and a proposal for posterior vaginal defect repair

To get support from morphological findings to develop a novel surgical procedure for posterior vaginal defect repair, we histologically examined the rectum-vagina interface tissues obtained from 20 elderly female cadavers. The rectovaginal septum (RVS) was defined here as an elastic fiber-rich plate (EFRP) along the posterior vaginal wall. It lined the posterior surface of the vein-rich zone of the vaginal wall and extended between the bilateral paracolpiums. The septum was more evident in the lower half of the interface than in the upper half. The RVS was often thin and interrupted. Since the RVS was not so clearly demonstrated in the upper vagina histologically, augmentation using some implant is considered to be necessary for the enterocele and high rectocele. Since the thickness and tightness of the RVS vary with the case in the lower vagina, surgical procedures for low rectocele repair should be individualized, including implant-augmentation.

A clinicoanatomical study of the novel nerve fibers linked to stress urinary incontinence: the first morphological description of a nerve descending properly along the anterior vaginal wall

When performing anterior colporrhaphy for cystocele, most pelvic surgeons have not considered the neuroanatomy that contributes to urethral function. The aim of the study was to anatomically identify nerve fibers located in the anterior vagina associated with the pathogenesis of incontinence and pelvic organ prolapse. Anterior vaginal specimens were obtained from 17 female cadavers and 33 cases of clinical cystocele by anterior vaginal resection. The specimens were step-sectioned and stained with hematoxylin-eosin, S100 antibody, and tyrosine hydroxylase antibody. As a result, descending nerves 50-200 microm in thickness were identified between the urethra and vagina. They were located more than 10 mm medially from a cluster of nerves found almost along the lateral edge of the vagina and stained with S100 and tyrosine hydroxylase antibody, originated from the cranial part of the pelvic plexus, and appeared to terminate at the urethral smooth muscles. The authors classified the density of S100 positive nerve fibers in the anterior vaginal wall obtained from clinically operated cases of cystocele into three grades (Grade 1, nothing or a few thin nerves less than 20 microm in diameter; Grade 2, thick nerves more than 50 microm in diameter and thin nerves; Grade 3, more than 3 thick nerves in one field at an objective magnification of 40x). Mean urethral mobility (Q-tip) values (28.1 degrees +/-+/- 19.6 degrees ) observed in the Grade 3 cases was significantly lower than those (50.0 degrees +/-+/- 27.4 degrees and 59.4 degrees +/-+/- 19.9 degrees ) in Grade 2 and Grade 1, respectively. In addition, the presence of preoperative or postoperative stress urinary incontinence in the cases of Grade 1 was significantly higher than those of the cases with S100 positive stained nerves. In conclusion, the novel nerve fibers immunohistochemically identified in the anterior vaginal wall are different from those of the common nervous system or the pelvic floor and are associated with the pathogenesis of urethral hypermobility.