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Transverse sections of the anal canal and natal skin cleft (85 years old male). (A) A level of the inferior end of the coccyx (CO) contains the most superior part of the anococcygeal ligament (ACL). (B) A level 40 mm inferior side of the CO. A fibrous tissue extends between the natal cleft (skin) and the external anal sphincter (EAS). (C) A higher magnification view of a square in panel A. Arrows show smooth muscles in the ligament. (D) A higher magnification view of a square in panel B. Arrows show striated muscles in the subcutaneous fibrous tissue. LA, levator ani muscle; GM, gluteus maximus muscle.
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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.
We examined the horizontal sections of 15 fetuses as well as adult histolog...
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Context 1
... and extended along the supero-inferior axis be- tween the bilateral gluteus maximus muscles (Figs. 2B, C and 3B). A gap between the gluteus muscles ranged from 18-40 mm at the level of the inferior end of the coccyx. The EAS did not connect with the fibrous tissue mass, but in- stead with the anococcygeal ligament (Fig. 2C). In 3 of 10 specimens (Fig. 3D), the dorsal fibrous tissue mass con- tained striated muscles continuous with the dorsosuperior reflection of the well-developed EAS as seen in Fig. ...Citations
... 3). Между мышцей, поднимающей задний проход, и тазовыми внутренностями (urethra, vagina, rectum) формируется промежуток, заполненный аморфной тканью, названной ligamentum hiatale [21][22][23][24][25][26]. ...
Pelvic floor and perineum muscles play an important role in the formation of an apparatus supporting pelvic organs. The functional insufficiency of myofascial structures frequently leads to the development of urinary and fecal incontinence, erectile dysfunction, prolapse of internal organs, and perineal hernias formation. Back in the 20th century, morphologists focused on the skeletal muscles in pelvic floor and perineum, highlighting their leading role in supporting organs and creating intraabdominal pressure. However, in the past two decades, particular attention has been paid to the smooth muscle structures and their relationship with the musculoskeletal system in the pelvic outlet area. The new concept of the striated–smooth muscle complex provides the basis for revising various aspects of pelvic organ prolapse and urinary and fecal incontinence pathophysiology. We believe that this may lead to improved early diagnosis and prevention of diseases of the pelvic floor and perineum.
... It has a collagenous structure in the same plane as the LA. "Coccygeal muscular raphe" described by Courtney (1948Courtney ( , 1949, "levator raphe" described by Oh and Kark (1972), "levator plate" described by Strohbehn (1998), and "dorsal layer of the anococcygeal ligament" described by Kinugasa et al. (2011Kinugasa et al. ( , 2012 represent the same structure (Courtney 1948(Courtney , 1949Kinugasa et al. 2011Kinugasa et al. , 2012Oh and Kark 1972;Strohbehn 1998). The terminology for the structures located between the anal canal and coccyx is Fig. 1 Skeletal muscles of the pelvic outlet in women. ...
... It has a collagenous structure in the same plane as the LA. "Coccygeal muscular raphe" described by Courtney (1948Courtney ( , 1949, "levator raphe" described by Oh and Kark (1972), "levator plate" described by Strohbehn (1998), and "dorsal layer of the anococcygeal ligament" described by Kinugasa et al. (2011Kinugasa et al. ( , 2012 represent the same structure (Courtney 1948(Courtney , 1949Kinugasa et al. 2011Kinugasa et al. , 2012Oh and Kark 1972;Strohbehn 1998). The terminology for the structures located between the anal canal and coccyx is Fig. 1 Skeletal muscles of the pelvic outlet in women. ...
... The LA was found to be in broad planar contact with the obturator internus and has several muscle layers attached to the obturator fascia . Based on these anatomical findings, we assume a functional relationship in which the dynamic movement of the obturator internus cooperates with the LA through the obturator fascia, providing the foundation Courtney (1948Courtney ( , 1949 Iliorectococcygeus muscle Coccygeal muscular raphe The decussating fibers of the deep portion of the external anal sphincter as they insert into the skin Oh and Kark (1972) Levator raphe Anococcygeal raphe Shafik (1975Shafik ( , 1979Shafik ( , 1999 Hiatal ligament Anococcygeal raphe The posterior part of Intermediate loop Ayoub (1979a) Anococcygeal ligament Strohbehn (1998) Levator plate Kinugasa et al. (2011Kinugasa et al. ( , 2012 Ventral layer of the anococcygeal ligament Dorsal layer of the anococcygeal ligament Muro et al. (2014) Hiatal ligament Raphe of iliococcygeus muscle and pubococcygeus muscle ...
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.
... Over the last two decades, our group has examined large numbers of histological sections of anal canals in elderly subjects. These have included anterior walls in men [12,34] and women [25,31]; the lateral wall [2,9,16] and the posterior wall [13,15,17,18]. In them, we found no J-shapes EAS in the anterior and posterior anal walls, but aforementioned studies focused on sphincter-related nerves and fascial structures. ...
... For the previous studies [4,18,19], we prepared frontal sections of the anal canal from 12 human fetuses near term (crown-rump length or CRL, 228-315 mm; 28-38 gestational weeks). In the present study, we used these sections to ensure the presence of the J-shaped appearance of the EAS. ...
... We ensured our previous studies showing a well-developed longitudinal smooth muscle alongside the anal canal in fetuses [18,19]. Without a tight attachment to smooth muscles, the prenatal EAS appeared to extend freely and, when limited by the anal skin, it turned medially to provide a J-shaped curve. ...
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.
... The part posterior to the rectum, the posterior part, also contained SM cells and forms the posterior part of the endo-levator area. It corresponds to the anococcygeal ligament that goes from the coccyx to the anus between the slings of the LAM (Shafik, 1975;Kinugasa et al., 2011Kinugasa et al., , 2012Muro et al., 2014). Muro et al. already reported SM cells behind the rectum (Muro et al., 2014). ...
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.
... [Color figure can be viewed at wileyonlinelibrary.com] fundiformis of the CPM than in adults. In contrast, even in mid-term fetuses, there is a well-developed smooth muscle interface for the sphincter between rectum and striated muscle (Kinugasa et al., 2012(Kinugasa et al., , 2013. Consequently, the CPM does not seem to develop and grow to form the upper esophageal sphincter. ...
Histological examination of specimens from 22 donated elderly cadavers and 15 human fetuses revealed that the cricopharyngeus muscle (CPM) provided (1) posterior circular muscle fibers adjacent to the external aspect of the uppermost esophageal circular muscle and (2) a thin anterior sling connecting to that same muscle. Another thick lateral bundle of longitudinal muscle originated independently from a fascia covering the posterior cricoarytenoideus muscle, extended laterally and posteriorly, and occupied a space after the CPM had disappeared at the anterolateral angle of the esophagus below the cricoid. The thick fascia contained abundant elastic fibers along the internal surface of the pharyngeal constrictors (posteromedial elastic lamina), but was interrupted or discontinued near the cricoid origin of the CPM. As no submucosal smooth muscles or elastic fibers were connected to it, the CPM did not accompany a specific elastic structure at the interface between the pharyngeal and esophageal muscles. In fetuses, the medial half of the CPM was inserted into the cricoid while the lateral half continued to the sternothyroideus muscle or ended at a fascia covering the cricothyroideus. These anterolateral ends provided a mechanical load for longitudinal growth of the pharyngeal constrictors. Consequently, the CPM was unlikely to develop and grow to form the upper esophageal sphincter, and the muscle bundle crossing the lateral aspect of the pharyngo‐esophageal junction appeared to have a secondary passive role as a sphincter. This situation contrasts with that of another sphincter in the human body formed from striated muscle. Clin. Anat., 33:782–794, 2020. © 2019 Wiley Periodicals, Inc.
... This area directly connects the rectum and the LAM.Shafik called it the hiatal ligament(Shafik, 1999), and Arakawa the smooth muscle-mediated interface(Arakawa et al., 2010).The contingent posterior to the rectum, the posterior contingent, also contained smooth muscle cells and forms the posterior part of the endo-levator area. It corresponds to the anococcygeal ligament that goes from the coccyx to the anus between the slings of the LAM(Shafik, 1975;Kinugasa et al., 2011Kinugasa et al., , 2012. ...
Résumé : Introduction : Parmi les structures anatomiques impliqués dans la statique pelvienne, la continence urinaire et anale, le muscle élévateur de l’anus (MEA), le sphincter urétral (SU) et son innervation ont un rôle déterminant. Au cours de la grossesse, de l’accouchement par voie vaginale, de la chirurgie radicale pelvienne, des lésions des muscles du plancher pelvien ou de son innervation peuvent survenir. Ces lésions sont à l’origine de dysfonctions du plancher pelvien telle que le prolapsus uro-génital ou l’incontinence urinaire. Une meilleure connaissance de l’anatomie musculaire et nerveuse pelvi-périnéale est nécessaire pour diminuer la survenue et traiter ces troubles fonctionnels. Classiquement les muscles du plancher pelvien sont décrits comme entièrement striés sous contrôle somatique (nerf du MEA et/ou nerf pudendal (NP)). La dissection Anatomique Assisté par Ordinateur (DAAO) en utilisant des marqueurs nerveux et musculaires spécifiques peut aujourd’hui compléter les données établies par la dissection conventionnelle classique de sujets anatomiques.Objectif : L’objectif était de décrire l’innervation (origine, topographie, trajet, rapports, fonction) et la structure musculaire du MEA, de décrire l’innervation (origine, topographie, trajet, rapports, fonction) du sphincter urétral pour mettre en perspective les implications potentielles dans les dysfonctions du plancher pelvien.Méthodes : Nous avons étudié 9 fœtus humains (6 féminins et 3 masculins). Des coupes histologiques sériées de 5 µm d’épaisseur ont été effectuées dans les régions pelviennes de 7 fœtus âgés de 18 à 40 semaines de gestation. Pour chaque niveau de coupe, des lames ont été colorées puis traitées en immunohistochimie pour détecter : l’ensemble des fibres nerveuses (anticorps anti-protéine S100), les fibres autonomes cholinergiques (anti-VAChT), les fibres autonomes adrénergiques (anti-TH), les fibres autonomes nitrergiques (anti-nNOS), les fibres somatiques (anti-PMP 22), les fibres sensorielles (anti-CGRP), les fibres musculaires lisses (anti-SMA) et les fibres musculaires striées (anti-MYOG). Les coupes ont ensuite été numérisées par un scanner de haute résolution optique et les images ont été reconstruites en 3D avec le logiciel Winsurf®. Un fœtus additionnel a été entièrement destiné à réaliser de la microscopie électronique afin de confirmer nos résultats au niveau architectural musculaire.Résultats : Nous avons observé une innervation à la fois autonome (plexus hypogastrique inférieur (PHI)) et somatique (nerf du MEA et NP) du MEA. Nous avons individualisé des zones de cellules musculaires lisses au sein du plancher pelvien notamment de la partie médiane sous contrôle autonome (PHI) que nous nommons « compartiment médian musculaire lisse ».Nous avons systématisé le plancher pelvien musculaire en une zone médiale lisse sous contrôle nerveux autonome réalisant une interface entre les viscères pelviens, et une zone musculaire striée latérale sous contrôle nerveux somatique.Enfin, nous avons mis en évidence une double innervation à la fois somatique et autonome du sphincter urétral.Conclusion : La DAAO a permis de mettre en évidence une innervation pelvi-périnéale complexe avec l’intrication du système nerveux somatique et autonome. La fonction du contingent musculaire lisse pelvien reste à préciser.
... Using late-stage human fetuses near full term, we have previously investigated the fascial configuration in the limbs (Cho et al., 2018a,b), neck (Katori et al., 2012;, and retroperitoneal region (Kinugasa et al., 2008;Matsubara et al., 2009). At the stage, collagen and elastic fibers are well differentiated and can be easily discriminated using routine staining techniques (Kinoshita et al., 2013;Kinugasa et al., 2012). At the late fetal stage, a muscle-covering fascia is established even in the thigh, exhibiting a specific multilayered configuration (Cho et al., 2018b). ...
There seems to be no complete demonstration of the suboccipital fascial configuration. In 30 human fetuses near term, we found two types of candidate myodural bridge: (1) a thick connective tissue band running between the rectus capitis posterior major and minor muscles (rectus capitis posterior major [Rma], rectus capitis posterior minori [Rmi]; Type 1 bridge; 27 fetuses); and (2) a thin fascia extending from the upper margin of the Rmi (Type 2 bridge; 20 fetuses). Neither of these bridge candidates contained elastic fibers. The Type 1 bridge originated from: (1) fatty tissue located beneath the semispinalis capitis (four fetuses); (2) a fascia covering the multifidus (nine); (3) a fascia bordering between the Rma and Rmi or lining the Rma (13); (4) a fascia covering the inferior aspect of the Rmi (three); and (5) a common fascia covering the Rma and obliquus capitis inferior muscle (nine). Multiple origins usually coexisted in the 27 fetuses. In the minor Type 2 bridge, composite fibers were aligned in the same direction as striated muscle fibers. Thus, force transmission via the thin fascia seemed to be effective along a straight line. However, in the major Type 1 bridges, striated muscle fibers almost always did not insert into or originate from the covering fascia. Moreover, at and near the dural attachment, most composite fibers of Type 1 bridges were interrupted by subdural veins and dispersed around the veins. In newborns, force transmission via myodural bridges was likely to be limited or ineffective. The postnatal growth might determine a likely connection between the bridge and headache. Clin. Anat. 32:914–928, 2019. © 2019 Wiley Periodicals, Inc.
... In the patient group, there was a positive correlation between the H angle (formed by posterosuperior reflection of the EAS) and EAS thickness at all levels of the anal canal. Several anatomical studies can be found regarding dorsosuperior reflection of the well developed EAS in the literature [29,30]. According to our observations on midsagittal MR images, this reflection was not distinct in every subject. ...
Subjects and methods:
Forty-seven consecutive patients with chronic anal fissure and randomly selected 40 patients who had no claims for perianal disease during their life time were included in the study. T2-weighted sagittal, high-resolution (HR) T2-weighted, and contrast-enhanced fat-suppressed T1-weighted oblique axial and oblique coronal images were retrospectively analyzed by two observers in consensus. Thickness of sphincteric muscles, anal canal length, anorectal angle, thickness of anococcygeal ligament, depth of Minor triangle, width between subcutaneous sphincters, vascularity of posterior commissure, visibility of posterosuperior projection of external sphincter, and angle between the distal anal canal and posterosuperior projection of external sphincter (H angle) in patients and in controls were compared and analyzed using t test, Mann-Whitney U test, and Spearman correlation.
Results:
The patients with chronic anal fissure had longer anal canal (51.50 mm ± 0.91 vs. 44.11 mm ± 0.71; p = 0.000), thicker internal anal sphincter muscle at mid-anal level (4.18 ± 0.15 vs. 3.39 ± 0.07; p = 0.007), and wider space between subcutaneous external sphincters (11.39 ± 0.50 vs. 6.89 ± 0.22; p = 0.000). In patients, there was a positive correlation between H angle and external sphincter thickness at proximal (r = 0.347; p = 0.021), middle (r = 0427; p = 0.000), and distal (r = 0.518; p = 0.000)) levels of the anal canal. CONCLUSıON: 3.0 Tesla MR imaging provides detailed information about the morphometric changes in the anal sphincter muscles in patients with chronic anal fissure.
... The bilayered appearance of the pubovisceral muscle is reminiscent of the multilayered architecture of the LAM in some dissections [6,18,19]. A further difference between our sectional and dissectional studies is that the area, in which we and others [1] identified the smooth rectococcygeal muscle, is described as the midline raphe of the LAM [24] or the anterior layer of the anococcygeal ligament [25,26]. ...
Background:
Pelvic-floor anatomy is usually studied by artifact-prone dissection or imaging, which requires prior anatomical knowledge. We used the serial-section approach to settle contentious issues and an interactive 3D-pdf to make the results widely accessible.
Method:
3D reconstructions of undeformed thin serial anatomical sections of 4 females and 2 males (21-35y) of the Chinese Visible Human database.
Findings:
Based on tendinous septa and muscle-fiber orientation as segmentation guides, the anal-sphincter complex (ASC) comprised the subcutaneous external anal sphincter (EAS) and the U-shaped puborectal muscle, a part of the levator ani muscle (LAM). The anococcygeal ligament fixed the EAS to the coccygeal bone. The puborectal-muscle loops, which define the levator hiatus, passed around the anorectal junction and inserted anteriorly on the perineal body and pubic bone. The LAM had a common anterior attachment to the pubic bone, but separated posteriorly into puborectal and "pubovisceral" muscles. This pubovisceral muscle was bilayered: its internal layer attached to the conjoint longitudinal muscle of the rectum and the rectococcygeal fascia, while its outer, patchy layer reinforced the inner layer. ASC contraction makes the ano-rectal bend more acute and lifts the pelvic floor. Extensions of the rectal longitudinal smooth muscle to the coccygeal bone (rectococcygeal muscle), perineal body (rectoperineal muscle), and endopelvic fascia (conjoint longitudinal and pubovisceral muscles) formed a "diaphragm" at the inferior boundary of the mesorectum that suspended the anorectal junction. Its contraction should straighten the anorectal bend.
Conclusion:
The serial-section approach settled contentious topographic issues of the pelvic floor. We propose that the ASC is involved in continence and the rectal diaphragm in defecation.
... Shafik [24] provided a concept "the hiatal ligament" to the entire connective tissue occupying the urogenital hiatus, but this term is recently used for the perianal tissue (reviewed by Kinugasa et al. [25]). We do not deny a possibility that large urogenital hiatus shown in the present study is a result of degeneration of the LA with age [26]. ...
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.
