Superficial Transverse Perineal Muscle Research Articles

Skeletal Muscle Complex Between the Vagina and Anal Canal: Implications for Perineal Laceration.

The anatomy of the skeletal muscles located between the vagina and anus is important during complex obstetric laceration reconstructions. We aimed to clarify the composition of skeletal muscles located between the vagina and anal canal and their three-dimensional configuration relevant to perineum repair. This observational study involved ten female cadavers. An anatomical dissection was performed to observe the muscles around the vagina and anal canal. Immunohistological analysis of the midsagittal section was performed to clarify the composition of the muscles, and dissection was performed to correspond to the cross-section. Wide-range serial sectioning and three-dimensional reconstruction were used to support these findings histologically and visualize the three-dimensional arrangement. The region between the vagina and anal canal included the anterior part of the external anal sphincter, superficial transverse perineal muscle approaching from the lateral side, and levator ani, located cranially. They converge three-dimensionally in the median from each direction, forming a muscle complex between the vagina and anal canal. The medial region between the vagina and anal canal in those giving birth includes a skeletal muscle complex formed by the confluence of the external anal sphincter, anterior bundle of the levator ani, and superficial transverse perineal muscle. In cases of severe perineal lacerations, these muscles could be injured. The anatomical knowledge that a part of the levator ani forms a muscle sling anterior to the anal canal is particularly important for obstetricians and gynecologists repairing obstetric lacerations and treating pelvic floor disorders.

Anatomical and histological investigation of the area anterior to the anorectum passing through the levator hiatus

Objective: To document the anatomical structure of the area anterior to the anorectum passing through the levator hiatus between the levator ani slings bilaterally. Methods: Three male hemipelvises were examined at the Laboratory of Clinical Applied Anatomy, Fujian Medical University. (1) The anatomical assessment was performed in three ways; namely, by abdominal followed by perineal dissection, by examining serial cross-sections, and by examining median sagittal sections. (2) The series was stained with hematoxylin and eosin to enable identification of nerves, vessels, and smooth and striated muscles. Results: (1) It was found that the rectourethralis muscle is closest to the deep transverse perineal muscle where the longitudinal muscle of the rectum extends into the posteroinferior area of the membranous urethra. The communicating branches of the neurovascular bundle (NVB) were identified at the posterior edge of the rectourethralis muscle on both sides. The rectum was found to be fixed to the membranous urethra through the rectourethral muscle, contributing to the anorectal angle of the anterior rectal wall. (2) Serial cross-sections from the anal to the oral side were examined. At the level of the external anal sphincter, the longitudinal muscle of the rectum was found to extend caudally and divide into two muscle bundles on the oral side of the external anal sphincter. One of these muscle bundles angled dorsally and caudally, forming the conjoined longitudinal muscle, which was found to insert into the intersphincteric space (between the internal and external anal sphincters). The other muscle bundle angled ventrally and caudally, filling the gap between the external anal sphincter and the bulbocavernosus muscle, forming the perineal body. At the level of the superficial transverse perineal muscle, this small muscle bundle headed laterally and intertwined with the longitudinal muscle in the region of the perineal body. At the level of the rectourethralis and deep transverse perineal muscle, the external urethral sphincter was found to occupy an almost completely circular space along the membranous part of the urethra. The dorsal part of the external urethral sphincter was found to be thin at the point of attachment of the rectourethralis muscle, the ventral part of the longitudinal muscle of the rectum. We identified a venous plexus from the NVB located close to the oral and ventral side of the deep transverse perineal muscle. Many vascular branches from the NVB were found to be penetrating the longitudinal muscle and the ventral part of rectourethralis muscle at the level of the apex of the prostate. The rectourethral muscle was wrapped ventrally around the membranous urethra and apex of the prostate. The boundary between the longitudinal muscle and prostate gradually became more distinct, being located at the anterior end of the transabdominal dissection plane. (3) Histological examination showed that the dorsal part of the external urethral sphincter (striated muscle) is thin adjacent to the striated muscle fibers from the deep transverse perineal muscle and the NVB dorsally and close by. The rectourethral muscle was found to fill the space created by the internal anal sphincter, deep transverse perineal muscle, and both levator ani muscles. Many tortuous vessels and tiny nerve fibers from the NVB were identified penetrating the muscle fibers of the deep transverse perineal and rectourethral muscles. The structure of the superficial transverse perineal muscle was typical of striated muscle. These findings were reconstructed three-dimensionally. Conclusions: In intersphincteric resection or abdominoperineal resection for very low rectal cancer, the anterior dissection plane behind Denonvilliers' fascia disappears at the level of the apex of the prostate. The prostate and both NVBs should be used as landmarks during transanal dissection of the non-surgical plane. The rectourethralis muscle should be divided near the rectum side unless tumor involvement is suspected. The superficial and deep transverse perineal muscles, as well as their supplied vessels and nerve fibers from the NVB. In addition, the cutting direction should be adjusted according to the anorectal angle to minimize urethral injury.

Anatomy of Cowper\u2019s 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.

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

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. 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. 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 453min and median blood loss was 46g. There was 1 (7.1%) circumferential-positive case, but no cases of urethral injury or rectal perforation. The 2-team TpAPR procedure is beneficial for appropriate dissection of the anterior side during APR surgery.

Postpartum perineal pain and dyspareunia related to each superficial perineal muscle injury: a cohort study.

To assess the association between superficial perineal muscle trauma and perineal pain and dyspareunia. Prospective cohort study of 405 women with a spontaneous vaginal birth comparing an intact perineum and first-degree perineal trauma group (n =205) with a second-degree perineal trauma and episiotomy group (n =200). Perineal pain was measured at 2days, 10days, 7weeks, 3months and 6months postpartum. Dyspareunia was assessed at 7weeks, 3months and 6months postpartum. All second-degree perineal traumas and episiotomies involved damage to the bulbospongiosus muscle (BSM), but not always to the superficial transverse perineal muscle (STPM). In case of second-degree trauma or episiotomy, the odds of pain at 10days and dyspareunia at 6 months postpartum were four- and five-fold greater, respectively, than if the perineum had remained intact or suffered a first-degree perineal trauma [OR 4.4 (95% CI: 2.8-6.9) and OR 5.5 (95% CI: 2.8-10.9), respectively]. When comparing injuries where > 50% BSM ± STPM against those with < 50% BSM torn, pain was significantly higher at 10days postpartum [OR 1.9 (95% CI: 1.1-3.6], with no difference at 7weeks, while dyspareunia was significantly higher at 6 months postpartum [OR 3.3 (95% CI: 1.4-7.8)]. There was no difference in perineal pain or dyspareunia when comparing first-degree with < 50% BSM traumas. When perineal muscle trauma encompasses > 50% BSM ± STPM, perineal pain and dyspareunia persisted until 10days and 6months postpartum, respectively.

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.

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.

A surgical technique for secondary repair of obstetric anal sphincter injuries; sphinctero-vagino-perineoplasty.

Objective:This study was conducted to present the preliminary results of seven patients treated with sphinctero-vagino-perineoplasty for secondary repair of obstetric anal sphincter injuries.Materials and Methods:This retrospective study was conducted on the records of seven patients who underwent secondary repair of obstetric anal sphincter injuries at the colorectal surgery unit of a tertiary care center between February 2015 and December 2017.Results:All patients with solid stool incontinence were fully recovered at postoperative month 3. The Wexner incontinence score was significantly improved (decreased from 14.12 [range: 8-20] to 2.28 [range: 1-4]). The complication rate was 85.7% (wound infection, abscess, hematoma, detachment).Conclusion:Combined repair of anal sphinchters, perineal body, superficial transverse perineal muscles, and bulbospongious muscles, which contribute to anal continence, may improve surgical outcomes in patients with obstetric anal sphincter injuries.

A functional and clinical reinterpretation of human perineal neuromuscular anatomy: Application to sexual function and continence.

Modern anatomical and surgical references illustrate perineal muscles all innervated by branches of the pudendal nerve but still organized into anatomically distinct urogenital and anal triangles with muscles inserting onto a central perineal body. However, these conflict with the anatomy commonly encountered during dissection. We used dissections of 43 human cadavers to characterize the anatomical organization of the human perineum and compare our findings to standard references. We found bulbospongiosus and the superficial portion of the external anal sphincter (EAS) were continuous anatomically with a common innervation in 92.3% of specimens. The superficial transverse perineal muscle inserted anterior and lateral to the midline, interdigitating with bulbospongiosus. The three EAS subdivisions were anatomically discontinuous. Additionally, in 89.2% of our sample the inferior rectal nerve emerged as a branch of S3 and S4 distinct from the pudendal nerve and innervated only the subcutaneous EAS. Branches of the perineal nerve innervated bulbospongiosus and the superficial EAS and nerve to levator ani innervated the deep EAS. In conclusion, we empirically demonstrate important and clinically relevant differences with perineal anatomy commonly described in standard texts. First, independent innervation to the three portions of EAS suggests the potential for functional independence. Second, neuromuscular continuity between bulbospongiosus and superficial EAS suggests the possibility of shared or overlapping function of the urogenital and anal triangles. Clin. Anat. 29:1053-1058, 2016. © 2016 Wiley Periodicals, Inc.

New Insights into the Anatomy of the Bulbospongiosus Muscle and Its Role in the Composition of the External Anal Sphincter in Humans

Traditional descriptions of the bulbospongiosus muscle in males and females describe a striated muscle overlying the most proximal portion of the corpus spongiosus, the bulb of the penis in males, and the bulbs of the vestibule in females. Likewise, in both sexes the bulbospongiosus muscle and the superficial transverse perineal muscles are described as inserting at the midline on the perineal body. In dissections of forty (40) human cadavers we found both of these descriptions do not accurately characterize the anatomy. In all forty cadavers examined, as suggested by the embryology literature, the adult bulbospongiosus continues from the urogenital triangle to the anal triangle as an uninterrupted ring of muscle that forms the superficial portion of the external anal sphincter and passes deep and lateral to the perineal body without insertion. Additionally, the superficial transverse perineal muscle passes anteriorly and superiorly to insert onto the bulbospongiosus muscle, and does not follow traditional descriptions asserting that this muscle continues medially from the ischial tuberosities to the perineal body. The perineal body is inferior to the rest of the perineum and in the great majority of cadavers we did not observe any muscle fibers inserting on the perineal body, again contradicting the published literature. Dissections of the external anal sphincter demonstrate that the subcutaneous external anal sphincter has a different fiber direction and is not continuous with the superficial external anal sphincter. Also, the deep external anal sphincter is continuous with the puborectalis muscle and is located deep to and separate from the superficial external anal sphincter. Therefore, we suggest that the traditionally conceived external anal sphincter, with three parts of a single muscle, is more usefully described as three individual muscles.Support or Funding InformationMidwestern University Intramural Funds

Perineal and Pelvic Anatomy of Extralevator Abdominoperineal Excision for Rectal Cancer: Cadaveric Dissection

Circumferential margin positivity and tumor perforations are the main reasons for the poor oncological outcome following standard abdominoperineal excision for low rectal cancer. The extralevator abdominoperineal excision approach has been developed to avoid "coning down" or "surgical waisting"; however, surgical education in this area has been neglected. This study aims to define correct surgical anatomical planes for extralevator abdominoperineal excision and show the differences in excision planes between standard and extralevator abdominoperineal excision. Macroscopic surgical dissections were performed in a clinical anatomy laboratory. The dissections were recorded as video clips. In accordance with the surgical technique of extralevator abdominoperineal excision, abdominal and then perineal dissections were performed on 1 female and 5 male cadavers. Neurovascular, muscular, and fascial structures located in or near the excision field were carefully revealed. The surgical planes of extralevator abdominoperineal excision, which widen the tumor-free margins and prevent inadvertent bowel perforation, are described in this step-by-step anatomical dissection study. Within the surgical excision planes, sacral vessels and sympathetic chains form a neurovascular network at the level of the sacrococcygeal joint. Although pelvic autonomic plexuses were away from the lateral incision line, their branches extending to urogenital organs were very close to the anterolateral dissection line. Perineal dissection showed that the internal pudendal vessels and pudendal nerve were close to the lateral excision plane. The superficial transverse perineal muscle and perineal body were the most important landmarks to determine the anterior boundary of dissection. The study focused on the perineal dissection of extralevator abdominoperineal excision. Successful extralevator abdominoperineal excision crucially depends on an accurate knowledge of surgical anatomical planes.

Deep Pelvic Anatomy Revisited for a Description of Crucial Steps in Extralevator Abdominoperineal Excision for Rectal Cancer

Extralevator abdominoperineal excision results in superior oncologic outcome for advanced low rectal cancer. The exact definition of surgical resection planes is pivotal to achieving negative circumferential resection margins. This study aims to describe the surrounding anatomical structures that are at risk for inadvertent damage during extralevator abdominoperineal excision. Joint surgical and macroanatomical dissection was performed in a university laboratory of clinical anatomy. A stepwise dissection study was conducted according to the technique of extralevator abdominoperineal excision by abdominal and perineal approaches in 4 human cadaveric pelvises. Muscular, fascial, tendinous, and neural structures were carefully exposed and related to the corresponding surgical resection planes. In addition to the autonomic nerves to be identified and preserved during total mesorectal excision, further structures endangered during extralevator abdominoperineal excision can be clearly identified. Terminal pudendal nerve branches come close to the surgical resection plane at the outer surface of the puborectal sling. Likewise, the pelvic plexus and its neurovascular bundles embedded within the parietal pelvic fascia extend close to the apex of the prostate where the parietal pelvic fascia has to be divided. These neural structures converge in the region of the perineal body, an area that provides no "self-opening" planes for surgical dissection. Thus, the necessity to sharply detach the anorectal specimen anteriorly from the perineal body and the superficial transverse perineal muscle bears the risk of both inadvertent damage of the aforementioned anatomical structures and perforation of the specimen. The study focused primarily on the macroscopic topography relevant to the surgical procedure, so that previously published histologic examinations were not performed. The present anatomical dissection study highlights those anatomical landmarks that require clear identification for the successful achievement of both negative circumferential resection margins and preservation of urogenital functions during extralevator abdominoperineal excision.

Perineal body anatomy in living women: 3-dimensional analysis using thin-slice magnetic resonance imaging

The objective of the study was to describe a framework for visualizing the perineal body's complex anatomy using thin-slice magnetic resonance (MR) imaging. Two millimeter thick MR images were acquired in 11 women with normal pelvic support and no incontinence/prolapse symptoms. Anatomic structures were analyzed in axial, sagittal, and coronal slices. Three-dimensional (3-D) models were generated from these images. Three distinct perineal body regions are visible on MR imaging: (1) a superficial region at the level of the vestibular bulb, (2) a midregion at the proximal end of the superficial transverse perineal muscle, and (3) a deep region at the level of the midurethra and puborectalis muscle. Structures are best visualized on axial scans, whereas craniocaudal relationships are appreciated on sagittal scans. The 3-D model further clarifies interrelationships. Advances in MR technology allow visualization of perineal body anatomy in living women and development of 3-D models that enhance our understanding of its 3 different regions: superficial, mid, and deep.

Perineal Hernia: Surgical Anatomy, Embryology, and Technique of Repair

Perineal hernia is the protrusion into the perineum of intraperitoneal or extraperitoneal contents through a congenital or acquired defect of the pelvic diaphragm. The first case was reported by de Garangeot in 1743. Perineal hernias may occur anteriorly or posteriorly to the superficial transverse perineal muscles. Congenital perineal hernia is a rare entity. Failure of regression of the peritoneal cul de sac of the embryo is considered a predisposing factor for hernia formation. Acquired perineal hernias are primary or secondary. Primarily acquired perineal hernias are caused by factors associated with increased intra-abdominal pressure. They are more common in females as a result of the broader female pelvis and the attenuation of the pelvic floor during pregnancy and childbirth. Secondarily acquired perineal hernias are incisional hernias associated with extensive pelvic operations such as abdominoperineal resection of the anorectum and pelvic exenteration. Pain in the perineal area, intestinal obstruction, topical skin erosion, and difficulty with urination necessitate the surgical repair of a perineal hernia. This can be accomplished through transabdominal, perineal, or combined abdominoperineal approaches. The defect in the muscles of the pelvic diaphragm may be closed either with direct suturing or by using autogenous tissues or synthetic mesh.

Bulbocavernosus Muscle Flap for the Repair of Vesicovaginal Fistula

Introduction: Anatomical studies on the bulbocavernosus muscle (BCM) and its supporting blood vessels were performed to explore the clinical roles of BCM flaps in the repair of complicated vesicovaginal fistulas. Methods: BCM and the supporting blood vessels of 15 female adult cadavers were anatomized. Pedicled BCM flaps were transposed to repair complicated vesicovaginal fistulas in 11 patients. Results: The left side of BCMs was 9.1 ± 1.8 cm in length and 1.5 ± 0.2 cm in width, whereas the right side was 9.0 ± 1.9 cm in length and 1.5 ± 0.4 cm in width. No significant difference between the two sides was identified (p > 0.05). The bulbocavernosus (BC) artery forms an angle with the superficial transverse perineal muscle at 64 ± 14° to the left and 68 ± 15° to the right. No significant difference between the two sides was found (p > 0.05). None of the 11 patients reported any postoperative urine leakage in the vagina or urinary incontinence. Follow-ups ranging from 6 months to 10 years found no urinary incontinence or urethral stricture; all patients have normal sexual function. Conclusion: Anatomical studies of BCM and its supporting blood vessels provide useful data for clinical application, especially the reduction of muscle flap death and the increase in the cure rate of complicated vesicovaginal fistulas.

Role of the Perineal Muscles in Micturition

Abstract The role of the superficial (STPM) and deep (DTPM) transverse perineal muscles during micturition is poorly addressed in the literature. We investigated the hypothesis that, at micturition, reflex contraction of the 4 perineal muscles occurs, which acts to fix the perineal body in its anatomic position and support the perineal floor and prevent its descent. The electromyographic (EMG) activity of STPMs and DTPMs as well as vesical pressure response to vesical balloon distension with carbon dioxide in increments of 20 mL were recorded in 26 healthy volunteers (16 men, 10 women, age 34.6 ± 6.7 years [mean ± standard deviation]). The test was repeated after individual anesthetization of the urinary bladder and perineal muscles with lidocaine and again after using saline instead of lidocaine. Big volumes of vesical balloon distension produced an increase of perineal muscles’ EMG activity and vesical pressure, both of which rose progressively with incremental increase of vesical distension. The latency exhibited gradual decrease on progressive increase of vesical distension. Perineal muscles did not respond to vesical distension after individual anesthetization of urinary bladder or perineal muscles but did respond to saline administration. Muscle response was similar from both sides. Vesical contraction at micturition appears to effect perineal muscles’ contraction. This action is suggested to be mediated through a reflex which we call “vesicoperineal reflex.” Perineal muscles’ contraction at micturition presumably supports perineal floor and protects perineal muscles from the high pressure induced by straining.

Surgical anatomy of the perineal muscles and their role in perineal disorders

The anterior perineum contains the perineal body and muscles. It is the site of functional and pathological disorders, many of which have not yet been related to a precise cause. In the present study, we investigated the anatomy of the perineal muscles with the aim of elucidating their function in light of their anatomic structure. Knowledge of their functional-structural relationship is deemed necessary for the understanding of the disorders that affect this part of the perineum. The perineal muscles of 28 cadaveric specimens were studied by direct dissection, as well as histologically. Fifteen male and 13 female specimens were collected from 18 adult (mean (+/- SD) age 31.6 +/- 9.8 years) and 10 neonate cadavers. Histological sections were stained with hematoxylin and eosin and Masson's trichrome stain. The fibers of the superficial transverse perineal muscle proceeded medially to decussate in a criss-cross pattern with the muscle fibers of the contralateral muscle; a few muscle fibers passed directly without decussation. Similarly, the fibers of the deep transverse perineal muscle decussated with their fellows on the opposite side. The two decussation raphes constituted the main bulk of the perineal body. A 'digastric' pattern could be identified for each of the superficial transverse perineal muscle and deep transverse perineal muscle. This pattern allows simultaneous contraction of the muscles on both sides as a single unit. The perineal muscles, forming the floor of the anterior perineum, are apparently subjected to variations in intra-abdominal pressure, which, if exceeding normal physiological limits, may lead to weakening, subluxation and sagging of the perineal muscles and, eventually, to perineocele. Further studies to investigate the role of the perineal muscles in the functional disorders of the perineum are needed.

Anatomy of the anal canal and perianal structures as defined by phased-array magnetic resonance imaging.

The anatomy of the anal canal and perianal structures has been imaged using endoluminal magnetic resonance imaging (MRI). Phased-array MRI avoids the use of an endoluminal coil that may distort anatomy. The aim of this study was to describe the anatomy of the anal canal and perianal structures using phased-array MRI. Imaging was performed in 14 men and 19 nulliparous women. The dimensions of the anal canal, puborectalis, external anal sphincter, perineal body, superficial transverse perineal muscle, bulbospongiosus, ischiocavernosus and anococcygeal body were measured in different planes, and sex differences were calculated. The lateral canal was significantly longer than its anterior and posterior part (P < 0.001). The anterior external anal sphincter was shorter in women than in men (P = 0.01) and occupied, respectively, 30 and 38 per cent of the anal canal length (P = 0.001). The caudal ends of the external anal sphincter formed a double layer. The perineal body was thicker in women than in men (P < 0.001) and easier to define. The superficial transverse muscles had a lateral and caudal extension to the ischiopubic bones. The bulbospongiosus was thicker in men than in women (P < 0.001). The ischiocavernosus and anococcygeal body had the same dimensions in both sexes. Phased-array MRI is a non-invasive technique that allows an accurate description of the normal anatomy of the anal canal and perianal structures.

Normal anal sphincter anatomy and age- and sex-related variations at high-spatial-resolution endoanal MR imaging.

To describe the various patterns of normal sphincter anatomy as seen at endoanal magnetic resonance (MR) imaging and to assess sex- and age-related variations in the dimensions of the anal sphincter to refine the diagnosis of sphincter disorders. Endoanal MR imaging (1.5 T) was performed in 100 healthy volunteers (50 women, 50 men) evenly distributed between ages 20 and 85 years. The essential anatomic structures were evaluated, and various patterns in men and women were recorded. The thickness of the anal sphincter muscles and the length of the anal canal were measured, and age- and sex-related correlations were studied. Sex-related differences included a significantly shorter external sphincter in women than in men both laterally (mean, 27.1 mm +/- 5.4 vs 28.6 mm +/- 4.3; P: <.05) and anteriorly (mean, 14.0 mm +/- 3.0 vs 27.0 mm +/- 53.0; P: <.051). The superficial transverse perineal muscle is located more superiorly in women than in men. The central perineal tendon in men is a central muscular insertion point; in women, it represents an area where muscle fibers imbricate. Age-related variations included a significant decrease in the thickness of the external sphincter in men (P: <.01). Significant decrease in the thickness of the longitudinal muscle and increase in the thickness of the internal sphincter were noted in both sexes (P: <.01). High-spatial-resolution endoanal MR imaging provides excellent visualization of pelvic floor structures. Severe atrophy as it occurs in incontinent patients should be differentiated from physiologic, age-related thinning of the external sphincter and longitudinal muscle.

The use of superficial transverse perineal muscles in the treatment of post surgical anal incontinence.

Los Angeles, Calif. Department of Surgery, Cedars of Lebanon Hospital, and the University of Southern California Medical School, Los Angeles.