Spatial distribution of smooth muscle tissue in the male pelvic floor with special reference to the lateral extent of the rectourethralis muscle: Application to prostatectomy and proctectomy

[Surgical anatomy of the anorectum]

The anorectum corresponds to the last segment of the gastrointestinal tract and is responsible for mediating fecal continence and controlled defecation. An understanding of the complex topographic anatomy is an indispensable prerequisite for the surgical treatment of benign and malignant diseases in the anorectal region. The detailed description of perirectal fascia, anorectal blood supply and lymph vessel drainage, pelvic autonomic nerves and components of the anal canal and anal sphincter complex has significantly contributed to improvement of the oncological and functional surgical outcome. In this article the state of knowledge relating to the anorectal anatomy is outlined providing a practical basis for rectal and proctological surgical procedures.

Three-dimensional heterogeneity of smooth muscle fiber density anterior to the rectum in males: quantitative analysis with implications for transanal total mesorectal excision

PURPOSE

Transanal total mesorectal excision for rectal cancer in men poses a risk of urethral injury. The morphology of smooth muscle tissues around the rectum is reportedly characterized by differences in fiber density; however, quantitative analysis of these tissues for surgical applications is lacking. This study aimed to quantitatively analyze the histological properties of fiber density and the spatial extent of the smooth muscle anterior to the male rectum.

METHOD

This descriptive cadaveric study involving six adult cadavers was conducted at the Tokyo Medical and Dental University. Serial histological sections were prepared from tissues in the region anterior to the rectum, and immunostaining and 3D reconstruction were performed to evaluate the spatial distribution of the smooth muscle. Smooth muscle fiber densities were measured in different regions of the smooth muscle anterior to the rectum and statistically analyzed.

RESULTS

The three-dimensional heat map revealed a gradual change in fiber density within the smooth muscle anterior to the rectum, with lower density in the superior part and higher density in the inferior part. In mid-sagittal immunostained sections, the smooth muscle anterior to the rectum exhibited a significant difference in fiber density, averaging 23.22% ± 5.50% in the superior area and significantly higher at 46.99% ± 12.92% in the inferior area.

CONCLUSION

Heterogeneity in fiber density between the superior and inferior smooth muscle anterior to the rectum suggests that these differences could serve as landmarks, providing crucial positional information to avoid urethral injury during transanal total mesorectal excision.

Three-dimensional Analysis of the Distribution of Smooth and Skeletal Muscle Tissue Around the Female Urethra

INTRODUCTION AND HYPOTHESIS

The urethra is surrounded by layers of smooth muscle, including inner longitudinal and outer circler muscles, as well as the skeletal muscle of the external urethral sphincter. However, the extent of these muscles and their relationship with the levator ani (LA) remain unclear. This study aimed to clarify the composition of muscle layers around the female urethra and their three-dimensional arrangements.

METHODS

Pelvises from five female cadavers were collected for histological analysis. The surrounding urethral tissue was serially sectioned and stained with Elastica van Gieson stain to identify the connective and muscular tissues. Immunohistological staining with an anti-smooth muscle antibody was performed to confirm the distribution of the smooth and skeletal muscles. Thereafter, muscle layers were three-dimensionally reconstructed on the basis of serial histological sections.

RESULTS

The female urethra was surrounded by four muscle layers arranged from inner to outer layers in the following order: longitudinal smooth muscle, circular smooth muscle, the external urethral sphincter (EUS), and an outermost smooth muscle layer. These muscles surrounded the urethra and partially extended anteriorly. Moreover, smooth muscle fibers extending from the vagina were found between the LA and EUS.

CONCLUSIONS

This study clarified the distribution of muscle tissue surrounding the female urethra, showing that the EUS is connected to the LA through the outermost smooth muscle layer. Thus, urination control likely involves both the urethral muscle layers and the pelvic floor muscles.

Tailoring rectal cancer surgery: Surgical approaches and anatomical insights during deep pelvic dissection for optimal outcomes in low-lying rectal cancer

This review article explores advanced surgical approaches and anatomical insights for tailoring rectal cancer surgery, particularly focusing on low-lying rectal cancer. With the evolution of imaging technologies, precise preoperative planning has become possible, enhancing the visualization of anatomy surrounding the rectum and enabling more accurate assessments of circumferential resection margin (CRM) involvement. The article emphasizes the dynamic nature of rectal cancer treatment, advocating for individualized surgical planning based on comprehensive preoperative imaging and intraoperative assessment. This approach aims to optimize patient care by integrating recent advancements and anatomical insights into clinical practice for the management of low-lying rectal cancer. Particularly, the article discusses the importance of customizing the excision of Denonvilliers' fascia (DVF) based on tumor characteristics for optimal oncologic and functional outcomes, especially for anteriorly located tumors. It highlights the need for precise dissection techniques to ensure a negative CRM while preserving critical anatomical structures. Additionally, the review addresses the surgical management of tumors at the anorectal ring and introduces the Gate Approach for deep anterolateral pelvic dissection. Special attention is given to tumors impacting the membranous and prostate urethra, emphasizing tailored surgical approaches to balance complete tumor resection with the preservation of urogenital functions.

Anatomy of muscle connections in the male urethra and anorectal canal

OBJECTIVES

To elucidate the male urethral muscular structure and its relationship with the anorectal canal muscles, as establishing an anatomical foundation for urethral function will contribute to the prevention, diagnosis, and treatment of urinary incontinence.

METHODS

Eight male cadavers were used. Using a multifaceted approach, we performed macroscopic anatomical examination, histological analysis of wide-range serial sectioning and immunostaining, and three-dimensional (3D) reconstruction from histological sections. In the macroscopic anatomical examination, pelvic halves were meticulously dissected in layers from the medial aspect. In the histological analysis, the tissue, including the urethra and anorectal canal, was serially sectioned in the horizontal plane. The muscular structures were reconstructed and visualised in 3D.

RESULTS

The membranous portion of the urethra had three muscle layers: the longitudinal and circular muscles (smooth muscle) and the external urethral sphincter (skeletal muscle). The circular muscle was connected posteriorly to the longitudinal rectal muscle. The external urethral sphincter had a horseshoe shape, with its posterior ends continuing to the external anal sphincter, forming a 3D ring-like sphincter.

CONCLUSION

This study revealed skeletal and smooth muscle connections between the male urethra and anorectal canal, enabling urethral compression and closure. These anatomical muscle connections suggest a functional linkage between them.

Twisted orientation of the muscle bundles in the levator ani functional parts in women: Implications for pelvic floor support mechanism

This study presents a comprehensive investigation of the anatomical features of the levator ani muscle. The levator ani is a critical component of the pelvic floor; however, its intricate anatomy and functionality are poorly understood. Understanding the precise anatomy of the levator ani is crucial for the accurate diagnosis and effective treatment of pelvic floor disorders. Previous studies have been limited by the lack of comprehensive three-dimensional analyses; to overcome this limitation, we analysed the levator ani muscle using a novel 3D digitised muscle-mapping approach based on layer-by-layer dissection. From this examination, we determined that the levator ani consists of overlapping muscle bundles with varying orientations, particularly in the anteroinferior portion. Our findings revealed distinct muscle bundles directly attached to the rectum (LA-re) and twisted muscle slings surrounding the anterior (LA-a) and posterior (LA-p) aspects of the rectum, which are considered functional parts of the levator ani. These results suggest that these specific muscle bundles of the levator ani are primarily responsible for functional performance. The levator ani plays a crucial role in rectal elevation, lifting the centre of the perineum and narrowing the levator hiatus. The comprehensive anatomical information provided by our study will enhance diagnosis accuracy and facilitate the development of targeted treatment strategies for pelvic floor disorders in clinical practice.

International standardization and optimization group for intersphincteric resection (ISOG-ISR): modified Delphi consensus on anatomy, definition, indication, surgical technique, specimen description and functional outcome

AIM

Intersphincteric resection (ISR) is an oncologically complex operation for very low-lying rectal cancers. Yet, definition, anatomical description, operative indications and operative approaches to ISR are not standardized. The aim of this study was to standardize the definition of ISR by reaching international consensus from the experts in the field. This standardization will allow meaningful comparison in the literature in the future.

METHOD

A modified Delphi approach with three rounds of questionnaire was adopted. A total of 29 international experts from 11 countries were recruited for this study. Six domains with a total of 37 statements were examined, including anatomical definition; definition of intersphincteric dissection, intersphincteric resection (ISR) and ultra-low anterior resection (uLAR); indication for ISR; surgical technique of ISR; specimen description of ISR; and functional outcome assessment protocol.

RESULTS

Three rounds of questionnaire were performed (response rate 100%, 89.6%, 89.6%). Agreement (≥80%) reached standardization on 36 statements.

CONCLUSION

This study provides an international expert consensus-based definition and standardization of ISR. This is the first study standardizing terminology and definition of deep pelvis/anal canal anatomy from a surgical point of view. Intersphincteric dissection, ISR and uLAR were specifically defined for precise surgical description. Indication for ISR was determined by the rectal tumour's maximal radial infiltration (T stage) below the levator ani. A new surgical definition of T3isp was reached by consensus to define T3 low rectal tumours infiltrating the intersphincteric plane. A practical flowchart for surgical indication for uLAR/ISR/abdominoperineal resection was developed. A standardized ISR surgical technique and functional outcome assessment protocol was defined.

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.

Novel combination method of wide-range serial sectioning and 3D reconstruction visualizing both macro-level dynamics and micro-level interactions in an attempt to analyze the female pelvic floor

The present report presents details of the method for combining wide-range serial sectioning and 3D reconstruction using an adult cadaver. For several decades, anatomists have utilized a variety of non-destructive three-dimensional (3D) visualization methods to complement gross anatomical analysis methods. These include vascular casting for the visualization of vascular morphology and micro-CT for the visualization of bone morphology. However, these conventional methods are restricted by the properties and sizes of the target structures. Here, we introduce a method to conduct 3D reconstruction based on wide-range serial histological sections from adult cadavers, which overcomes previous restrictions. An attempt at 3D visualization of the female pelvic floor muscles provides a detailed description of the procedure. Supplemental video and 3D PDF files allow multifaceted observation of 3D images. Wide-range serial sectioning visualizes morphology beyond the scope of conventional methods, while 3D reconstruction enables non-destructive 3D visualization of any structure that can be observed on a histological section, including skeletal muscle, smooth muscle, ligaments, cartilage, connective tissue, blood vessels, nerves, lymph nodes, and glands. The novel combination of both methods is instrumental in meso-anatomy, a discipline intermediate between macro-anatomy and micro-anatomy.

Posterior tibial nerve stimulation as a neuromodulation therapy in treatment of neurogenic overactive bladder in multiple sclerosis: A prospective randomized controlled study

BACKGROUND

one of the major annoying disorders occurring in people with multiple sclerosis is lower urinary tract disorders (LUT). Urgency is considered the main one seriously influencing the quality of life. Neurogenic detrusor over activity (DOAB) is characterized by a hyperreflexic, overactive detrusor that responds quickly to low-intensity sensory input from general visceral afferent fibers. Overactivity has been claimed to induce random, uncontrolled contractions of the detrusor muscle, leading to intravesicular pressure rise, producing urgency, frequency, and consequently incontinence AIM: To demonstrate the therapeutic efficacy for posterior tibial nerve stimulation (PTNS) in neurogenic over active bladder (NOAB) in people with multiple sclerosis METHODS: The current trial is a prospective, randomized controlled study. Forty remitting relapsing males with MS with moderate NOAB symptoms were randomly assigned into two equal groups; control group (C) treated by selected therapeutic exercises program for strengthening pelvic floor muscles and an intervention group (ES) receiving an additional posterior tibial nerve electrical stimulation. Each session ranged from 45- 50 minutes, three days weekly for a month. Outcome measures were recorded before starting the treatment and after termination of the study intervention and included over active bladder symptoms score (OVBS) score, urodynamic parameters (uroflow, filling and voiding cystometry), and post voiding residual volume by abdominal ultrasound RESULTS: There was a significant improvement of all voiding parameters compared to baseline and the group C except frequency of urgency incontinence. A significant decrease was detected in post-treatment mean episodes number of nighttime frequency, urgency, urgency incontinence (1.65 ± 0.93, 1.2 ± 0.52 and 1.5 ± 0.76) respectively of the ES group compared to that of group C (3.05 ± 1.09, 2.25 ± 0.71 and 2.25 ± 1.06) (P < 0.01). There was a significant decrease in median post-treatment OVBS score 3 (3-3) compared to group C median score 5 (6-4). A statistically significant improvement was observed of all urodynamic parameters (bladder capacity and compliance, Detrusor overactivity (DO), maximum flow rate and post voidal residual volume in the ES group compared to the group C CONCLUSION: PTNS is a promising and potentially beneficial treatment option for NOAB symptoms in males with MS and superior to pelvic floor muscle training alone.

Transperineal abdominoperineal resection in the prone jackknife position in male patients with low rectal cancer

INTRODUCTION

In male patients with low rectal cancer undergoing abdominoperineal resection (APR), successful dissection of the anterior anorectum is key to reducing the risk of circumferential resection margin involvement, intraoperative bowel perforation, and local recurrence, but it is challenging. To overcome difficulties dissecting the anterior anorectum, we present a safe and feasible procedure using a transperineal endoscopic approach during APR (TpAPR).

MATERIALS AND SURGICAL TECHNIQUE

The male patient is placed in the prone jackknife position. TpAPR precedes the procedure from an abdominal approach. We use some pelvic tissues as clear anatomical landmarks to dissect the anterior anorectum. The key steps of this procedure are shown in the video.

DISCUSSION

The identification of a clear anatomical dissection plane of the anterior anorectum is difficult because of the complex surgical anatomy of the region. Clear anatomical landmarks for dissection of the anterior anorectum are necessary for safe implementation of this procedure. Therefore, TpAPR in the prone jackknife position can be performed to obtain better visualization of each anatomical landmark at a glance.

Robotic Intersphincteric Resection for Low Rectal Cancer: Technical Controversies and a Systematic Review on the Perioperative, Oncological, and Functional Outcomes

Intersphincteric resection (ISR) is the ultimate anus-sparing technique for low rectal cancer and is considered an oncologically safe alternative to abdominoperineal resection. The application of the robotic approach to ISR (RISR) has been described by few specialized surgical teams with several differences regarding approach and technique. This review aims to discuss the technical aspects of RISR by evaluating point by point each surgical controversy. Moreover, a systematic review was performed to report the perioperative, oncological, and functional outcomes of RISR. Postoperative morbidities after RISR are acceptable. RISR allows adequate surgical margins and adequate oncological outcomes. RISR may result in severe bowel and genitourinary dysfunction affecting the quality of life in a portion of patients.

Anus-Preserving Surgery in Advanced Low-Lying Rectal Cancer: A Perspective on Oncological Safety of Intersphincteric Resection

The surgical management of low-lying rectal cancer, within 5 cm from the anal verge (AV), is challenging due to the possibility, or not, to preserve the anus with its sphincter muscles maintaining oncological safety. The standardization of total mesorectal excision, the adoption of neoadjuvant chemoradiotherapy, the implementation of rectal magnetic resonance imaging, and the evolution of mechanical staplers have increased the rate of anus-preserving surgeries. Moreover, extensive anatomy and physiology studies have increased the understanding of the complexity of the deep pelvis. Intersphincteric resection (ISR) was introduced nearly three decades ago as the ultimate anus-preserving surgery. The definition and indication of ISR have changed over time. The adoption of the robotic platform provides excellent perioperative results with no differences in oncological outcomes. Pushing the boundaries of anus-preserving surgeries has risen doubts on oncological safety in order to preserve function. This review critically discusses the oncological safety of ISR by evaluating the anatomical characteristics of the deep pelvis, the clinical indications, the role of distal and circumferential resection margins, the role of the neoadjuvant chemoradiotherapy, the outcomes between surgical approaches (open, laparoscopic, and robotic), the comparison with abdominoperineal resection, the risk factors for oncological outcomes and local recurrence, the patterns of local recurrences after ISR, considerations on functional outcomes after ISR, and learning curve and surgical education on ISR.

Anatomy of Cowper's gland in humans suggesting a secretion and emission mechanism facilitated by cooperation of striated and smooth muscles

This study presents the detailed anatomy of the Cowper’s gland in humans. Elucidating the mechanism of secretion and emission of the Cowper’s gland requires analysis of the muscles around the Cowper’s gland. We hypothesized that the Cowper’s gland involves not only smooth muscle but also the striated muscles of the pelvic floor. Here, we provide comprehensive and three-dimensional anatomy of the Cowper’s gland and its surrounding structures, which overcomes the current local and planar understanding. In this study, seven male corpses of body donors were used to conduct macroscopic anatomy, histology, and three-dimensional reconstruction. The Cowper’s gland was surrounded laterally and posterosuperiorly by striated and smooth muscles, respectively. The striated muscle bundle was connected from the superficial transverse perineal muscle, levator ani, and external anal sphincter to the external urethral sphincter (rhabdosphincter). The smooth muscle was part of the deep transverse perineal muscle and entered between the bilateral Cowper’s glands and lobules. Our findings indicate that the secretion and emission of the Cowper’s gland in humans are carried out through the cooperation of striated and smooth muscles.

Usefulness of Endoscopic Tattooing Before Neoadjuvant Therapy in Patients with Clinical Complete Response in Locally Advanced Rectal Cancer for Providing a Safe Distal Surgical Margin

Background: Endoscopic tattooing of colorectal tumors enables tumor localization and determination of appropriate surgical margins. It becomes very difficult to detect the distal surgical margins (DSMs) of rectal tumors in patients who obtain clinical complete response (cCR) after neoadjuvant therapy. In this study, our aim is to examine the benefits of endoscopic tattooing of the tumor before neoadjuvant therapy in patients with locally advanced rectal cancer in accurate localization of the previous tumor and in providing appropriate DSMs in cases with cCR. Patients and Methods: The patients who were diagnosed with locally advanced rectal cancer, received neoadjuvant therapy and subsequently achieved cCR, and underwent surgery between January 2015 and October 2020 were included in the study. The patients were divided into two groups according to whether they were endoscopically tattooed before neoadjuvant chemoradiotherapy. Results: A total of 49 cases were included in the study. Significantly better DSMs were observed especially in female gender in the tattooed group. DSMs were found to be closer to the resection margins in the nontattooed group. It was found that endoscopic tattooing had a significant effect on the DSM in the regression analysis (P = .06, R² = 0.47). It was determined that laparoscopy or open surgery alone did not differ in terms of DSMs but open surgery together with tattooing was found to be strongly effective in providing larger DSMs. Conclusion: In locally advanced rectal cancer, endoscopic tattooing of the distal margin of the tumor before neoadjuvant therapy is a reliable and effective method for obtaining a safe DSM and not leaving the residual tumor at the lower end of anastomosis, especially in cases of cCR.

The series of smooth muscle structures in the pelvic floors of men: Dynamic coordination of smooth and skeletal muscles

Introduction

Recent studies have revealed the extended nature of smooth muscle structures in the pelvic floor, revising the conventional understanding of the “perineal body.” Our aim was to clarify the three‐dimensional configuration and detailed histological properties of the smooth muscle structures in the region anterior to the rectum and anal canal in men.

Materials and methods

Four male cadavers were subjected to macroscopic and immunohistological examinations. The pelvis was dissected from the perineal side, as in the viewing angle during transperineal surgeries. Serial transverse sections of the region anterior to the rectum and anal canal were stained with Masson's trichrome and immunohistological stains to identify connective tissue, smooth muscle, and skeletal muscle.

Results

There was a series of smooth muscle structures continuous with the longitudinal muscle of the rectum in the central region of the pelvic floor, and three representative elements were identified: the anterior bundle of the longitudinal muscle located between the external anal sphincter and bulbospongiosus; bilateral plate‐like structures with transversely‐oriented and dense smooth muscle fibers; and the rectourethral muscle located between the rectum and urethra. In addition, hypertrophic tissue with smooth muscle fibers extended from the longitudinal muscle in the anterolateral portion of the rectum and contacted the levator ani.

Conclusions

The series of smooth muscle structures had fiber orientations and densities that differed among locations. The widespread arrangement of the smooth muscle in the pelvic floor suggests a mechanism of dynamic coordination between the smooth and skeletal muscles.

Essential anatomy for total mesorectal excision and lateral lymph node dissection, in both trans-abdominal and trans-anal perspective

BACKGROUND AND PURPOSE

Total Mesorectal Excisions (TME) is the standard treatment of rectal cancer. It can be performed under laparoscopic, robotic or transanal approach. Inadvertent injury to surrounding structure like autonomic nerves is avoidable, no matter which approach is adopted. Lateral lymph node dissection (LLND) is a less commonly performed pelvic operation involving dissection in an unfamiliar area to most general surgeons. This article aims to clarify all the essential anatomy related to these procedures.

METHODS

We performed thorough literature search and revision on the pelvic anatomy. Our cases of TME and LLND, under either laparoscopic or transanal approach, were reviewed. We integrated the knowledge from literatures and our own experience. The result was presented in details, together with original figures and intra-operative photos.

MAIN FINDINGS

Anatomy of pelvic fascia, autonomic nerve system, anal canal and sphincter complex are core knowledge in performing TME and LLND.

CONCLUSIONS

Thorough understanding of the pelvic anatomy enables colorectal surgeons to master these procedures, avoid complication and perform extended resection. On the other hand, surgeons can appreciate the complex pelvic anatomy easier by seeing the pelvis in opposite angles (transabdominal and transaanal view).

Avoiding urethral and rectal injury during transperineal abdominoperineal resection in male patients with anorectal cancer

BACKGROUND

In abdominoperineal resection (APR) in male patients with rectal cancer, high margin involvement and urethral injury have been reported to result from difficulty in dissecting the anterior anorectum. Recently, the efficacy of an endoscopic down-to-up rectal dissection was reported. Here, we present a safe and simple technique for anterior dissection using a simultaneous laparoscopic and transperineal endoscopic approach.

METHODS

We perform transperineal APR (TpAPR) using both the laparoscopic and transperineal approach (a 2-team approach). Anterior dissection commences just behind the superficial transverse perineal muscle. Next, the striated muscle complex surrounding the rectum (levator ani and puborectalis muscle) is divided. At this point, it is difficult to identify the dissection plane between the membranous urethra and anterior rectum; thus, dissection along the lateral aspect of neurovascular bundle from the lateral to anterior side with the assistance of the laparoscopic team is helpful in identifying the posterior surface of the prostate. Once the prostate is identified, it is relatively easy to divide the rectourethralis muscles. The key steps of our procedure are shown in the video.

RESULTS

Between April 2016 and July 2019, we performed 14 TpAPR procedures in male patients with rectal cancer without distant metastasis. Extended surgery was performed in 8 patients, including pelvic sidewall dissection and combined resection of adjacent organs. Median operative time was 453 min and median blood loss was 46 g. There was 1 (7.1%) circumferential-positive case, but no cases of urethral injury or rectal perforation.

CONCLUSIONS

The 2-team TpAPR procedure is beneficial for appropriate dissection of the anterior side during APR surgery.

Transanal total mesorectal excision in the prone jackknife position without being conscious of the size of prostatic enlargement for lower rectal cancer

In 1982, it was demonstrated that a total mesorectal excision alone could achieve low rectal cancer recurrence rates in the pelvis and high disease-free survival rates. Nowadays, the total mesorectal excision is the gold-standard surgery for rectal cancer. Currently, the transanal total mesorectal excision has attracted attention as a promising alternative to the anterior approach. The transanal approach is superior to the anterior approach, because it facilitates total mesorectal excisions of the lower rectum, improves visualization, and shortens the surgical time. Some factors are particularly favorable for the transanal approach, including lesions in the lower third of the rectum, a narrow pelvis, a large tumor, male sex, and a prostatic enlargement. The transanal total mesorectal excision is commonly performed in the Lloyd-Davies position. However, in the Lloyd-Davies position, the sacral bone prevents the mobilized rectum from moving away from the pelvic base. From the perspective of pelvic morphology, we reasoned that, in the prone jackknife position, the mobilized rectum could spontaneously move toward the head, due to gravity, and this would broaden the pelvic surgical field. Consequently, this position could facilitate the transanal total mesorectal excision. Here, we described a transanal total mesorectal excision performed in the prone jackknife position for treating lower rectal cancer with a prostatic enlargement.

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.

An anatomical study of the anterior wall of the hypopharyngeal and the cervical esophageal junction

OBJECTIVE

The upper esophageal sphincter plays a significant role by forming a physical barrier at the junction of the hypopharynx and the cervical esophagus. As few studies have focused on the ventral aspect of this junction, the contribution of the anterior wall of the cervical esophagus to upper esophageal sphincter function remains unknown. The purpose of this study was to examine the muscle fibers' arrangement at the junction, especially of those forming its anterior wall.

METHODS

Thirteen specimens from 13 Japanese cadavers were analyzed. Six specimens were dissected macroscopically, while the remaining seven were examined histologically.

RESULTS

The outer longitudinal layer of the proximal esophagus was well-developed anterolaterally. The uppermost fibers of the inner circular layer of the esophagus ascended longitudinally. The anterolateral part of the outer longitudinal layer and the uppermost region of the inner circular layer were continuous with the median tendinous band, in turn reaching superior to the cricoid cartilage. Histological analysis showed that the tendinous band was also continuous with the superior part of the perichondrium of the cricoid cartilage and with the aponeurosis of the transverse and oblique arytenoids.

CONCLUSION

The well-developed anterolateral region of the outer longitudinal layer and the uppermost fibers of the inner circular layer were continuous with the median tendinous band, which reached superior to the cricoid cartilage. The contraction of the proximal esophagus may result in protrusion of the anteromedian esophageal wall into the lumen, thereby supporting the closure of the upper esophageal sphincter.

Three muscle slings of the pelvic floor in women: an anatomic study

The region anterior to the anal canal in women is composed of intertwined smooth and skeletal muscles. The present study aimed to clarify skeletal muscle morphology in the anterior region of the anal canal. The pelvic floor muscles of 28 pelvic halves from 16 female cadavers (mean age 79.75 years) were dissected from the inferior aspect to examine the perineal muscles, followed by midline transection and dissection from the inner surface to examine the pelvic outlet muscles. The bulbospongiosus muscle was found to be attached to the lateral surface of the external anal sphincter. The superficial transverse perineal muscle crossed superiorly to the bulbospongiosus and coursed medially toward its contralateral muscle bundle deep to the anterior portion of the external anal sphincter. The superficial transverse perineal muscle formed the middle sling. From the medial aspect, the anterior part of the levator ani was divided into anterior and posterior bundles to form the anterior and posterior slings, respectively. This study proposes that three muscular slings could be important in supporting the pelvic floor in women. In addition, this study shows that the anterior skeletal muscular wall of the anal canal is composed of the anterior muscle bundle of the levator ani, superficial transverse perineal, and proper external anal sphincter muscles.

Various significant connections of the male pelvic floor muscles with special reference to the anal and urethral sphincter muscles

The male pelvic floor is a complex structure formed by several muscles. The levator ani muscle and the perineal muscles are important components of the pelvic floor. The perineal muscles comprise the external anal sphincter, bulbospongiosus, superficial transverse perineal muscles, and ischiocavernosus. Although the connections of the muscles of the pelvic floor have been reported recently, the anatomical details of each muscle remain unclear. In this study, we examined the male pelvic floor to clarify the connection between the muscles related to function. Fifteen male pelvises were used for microscopic dissection, and three male pelvises were used for histological examination. On the lateral aspect, the perineal muscles were connected to each other. Bundles of the levator ani muscle extended to connect to the perineal muscles. In addition, the extended muscle bundle from the levator ani muscle and the perineal muscles surround the external urethral sphincter. On the medial aspect, the levator ani muscle and the external anal sphincter form the anterior and posterior muscular slings of the anal canal. The connection between the perineal muscles and levator ani muscle indicates a possible close relationship between the functions of the urethra and anus.

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.

Interactive three-dimensional teaching models of the female and male pelvic floor

Controversies regarding structure and function of the pelvic floor persist because of its poor accessibility and complex anatomical architecture. Most data are based on dissection. This "surgical" approach requires profound prior knowledge, because applying the scalpel precludes a "second look." The "sectional" approach does not entail these limitations, but requires segmentation of structures and three-dimensional reconstruction. This approach has produced several "Visible Human Projects." We dealt with limited spatial resolution and difficult-to-segment structures by proceeding from clear-cut to more fuzzy boundaries and comparing segmentation between investigators. We observed that the bicipital levator ani muscle consisted of pubovisceral and puborectal portions; that the pubovisceral muscle formed, together with rectococcygeal and rectoperineal muscles, a rectal diaphragm; that the external anal sphincter consisted of its subcutaneous portion and the puborectal muscle only; that the striated urethral sphincter had three parts, of which the middle (urethral compressor) was best developed in females and the circular lower ("membranous") best in males; that the rectourethral muscle, an anterior extension of the rectal longitudinal smooth muscle, developed a fibrous node in its center (perineal body); that the perineal body was much better developed in females than males, so that the rectourethral subdivision into posterior rectoperineal and anterior deep perineal muscles was more obvious in females; that the superficial transverse perineal muscle attached to the fibrous septa of the ischioanal fat; and that the uterosacral ligaments and mesorectal fascia colocalized. To facilitate comprehension of the modified topography we provide interactive 3D-PDFs that are freely available for teaching purposes. Clin. Anat. 33:275-285, 2020. © 2019 Wiley Periodicals, Inc.

Coexistence of Dense and Sparse Areas in the Longitudinal Smooth Muscle of the Anal Canal: Anatomical and Histological Analyses Inspired by Magnetic Resonance Images

Magnetic resonance images of the anal canal show small, circular, low‐intensity areas arranged in a row and a high‐intensity area surrounding them internally and externally in the longitudinal muscle layer that cannot be explained by current anatomical findings. The purpose of this study was to elucidate the detailed structure of the longitudinal smooth muscle of the anal canal and to interpret the magnetic resonance image of the longitudinal muscle. Specimens for macroscopic anatomy and histology were obtained from six and seven cadavers, respectively. The histological nature of the longitudinal muscle was examined by staining serial transverse and coronal sections of the lateral wall of the anal canal with Masson's trichrome stain and using immunohistochemistry for smooth and skeletal muscle fibers. Dense and sparse areas of smooth muscle fibers coexisted in the longitudinal muscle layer. The dense areas formed columnar muscle bundles approximately 1.0–1.5 mm in diameter, and they continued from the longitudinal muscle bundles of the rectum. The columnar muscle bundles of the longitudinal anal muscle were internally and externally surrounded by sparsely arranged smooth muscle fibers that ran longitudinally. The coexistence of dense and sparse areas of smooth muscle fibers suggests that the structure of the smooth muscle is optimized for its function. This histological nature is probably reflected in the magnetic resonance image of the longitudinal muscle as the coexistence of low‐ and high‐intensity areas. Clin. Anat. 33:619–626, 2020. © 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.

Anatomy of the smooth muscle structure in the female anorectal anterior wall: convergence and anterior extension of the internal anal sphincter and longitudinal muscle

AIM

The anatomy of the region between the vagina and anal canal plays an essential role when performing a proctectomy for low-lying tumours. However, the anatomical characteristics of this area remain unclear. The purpose of the present study was to clarify the configuration, and both lateral and inferior extensions, of the muscle bundles in the anorectal anterior wall in females.

METHODS

Using cadaveric specimens, macroscopic anatomical and histological evaluations were conducted at the anatomy department of our institute. Macroscopic anatomical specimens were obtained from six female cadavers. Histological specimens were obtained from eight female cadavers.

RESULTS

The smooth muscle fibres of the internal anal sphincter and longitudinal muscle extended anteriorly in the anorectal anterior wall of females and the muscle bundles showed a convergent structure. The anterior extending smooth muscle fibres merged into the vaginal smooth muscle layer, distributed subcutaneously in the vaginal vestibule and perineum and spread to cover the anterior surface of the external anal sphincter and the levator ani muscle. Relatively sparse space was observed in the region anterolateral to the rectum on histological analysis.

CONCLUSION

Smooth muscle fibres of the rectum and vagina are intermingled in the median plane, and there is relatively sparse space in the region anterolateral to the rectum. Therefore, when detaching the anorectal canal from the vagina during proctectomy, an approach from both the lateral sides should be used.

Transanal TME: new standard or fad?

Transanal total mesorectal excision (taTME) has been developed to overcome the difficulty of laparoscopic dissection and transection in the deep pelvis. TaTME has several clinical benefits over laparoscopic surgery, such as better exposure of the distal rectum and direct determination of distal resection margin. Although evidence demonstrating the true benefits of taTME over laparoscopic TME (LapTME) is still insufficient, accumulating data have revealed that, as compared with LapTME, taTME is associated with shorter operative time and a lower conversion rate without jeopardizing other short-term outcomes. However, taTME is a technically demanding procedure with specific complications such as urethral injury, and so sufficient experience of LapTME and step-by-step acquisition of the skills needed for this procedure are requisite. The role of transanal endoscopic surgery is expected to change, along with the recent progress in the treatment of rectal cancer, such as robotic surgery and the watch-and-wait strategy. Optimization of treatment will be needed in the future in terms not only of oncological but also of functional outcomes.