Videodefecography: a study of the rectal motile pattern

The mechanism of rectal motility has remained largely obscure. Recently, by recording rectal electromechanical activity, we identified the rectal motility pattern as occurring in a "mass squeeze" manner. In the current communication, rectal motility was studied by means of videodefecography. The study comprised 28 healthy volunteers (18 men, 10 women; mean age 37.6+/-11.8 years). Evacuation dynamics were studied and registered using a videocassette tape with a high-resolution recorder. The rectum showed no peristaltic or segmentation activity at rest. When the subject was asked to evacuate, a contraction wave started at the rectosigmoid junction (RSJ) and spread aborally. The upper rectum appeared to contract producing anal canal opening and the closure of the RSJ; after rectal evacuation, the anal canal closed and the RSJ opened. The rectal contraction wave was repeated as long as the rectum still contained barium paste. The subjects strained prior to the start of each contraction wave. Some waves did not effect rectal evacuation. These "incomplete" waves started at the mid- or lower rectum and were followed by "complete" waves that produced evacuation. In five of 28 subjects, rectal intussusception occurred during rectal contraction. A small anterior rectocele occurred in another two subjects during rectal contraction. Videodefecography revealed that upon rectal distension with barium paste, a contraction wave, initiated at the RSJ, effected reflex RSJ closure and anal canal opening. The wave spread aborally, "squeezing" the rectal contents towards the opened anal canal. Two types of contraction waves were observed: "complete" which produced rectal evacuation, and "incomplete" which failed to effect evacuation. Physiologic intussusception or rectocele were seen in a few subjects.     

不同型别的功能性便秘患儿肛门直肠测压对照研究

目的探讨功能性便秘（FC）患儿与健康儿童肛门直肠动力学差异,为其临床分型诊断及治疗提供依据。方法采用功能性胃肠病罗马Ⅲ诊断标准,收集2008年1月至2009年1月在第四军医大学唐都医院儿科门诊及住院的FC患儿为FC组。选取同期无消化系统症状,平日排便正常的健康儿童为正常对照组。采用不透光X线硫酸钡条测定结肠传输指数（TI）,依据TI将FC组分为出口梗阻型（OOC）亚组、慢传输型（STC）亚组和混合型（MIX）亚组。通过肛门直肠测压法分析FC各亚组与正常对照组肛门直肠动力学差异。结果研究期间FC组纳入25例,其中STC亚组10例,OOC亚组15例,未发现MIX患儿;正常对照组纳入10名。FC组与正常对照组肛门括约肌静息压差异无统计学意义（P〉0.05）。STC亚组肛门括约肌最大收缩压与正常对照组差异无统计学意义（P〉0.05）,OOC亚组肛门括约肌最大收缩压显著高于正常对照组及STC亚组（P〈0.05）。FC组直肠最低敏感量及最大耐受量均显著高于正常对照组（P均〈0.05）。STC亚组与OOC亚组直肠最低敏感量及最大耐受量差异均无统计学意义（P均〉0.05）。结论FC患儿存在明显的肛门直肠动力和感觉异常;OOC和STC患儿的肛门直肠动力学存在差异。肛门直肠测压检查对协助诊断FC有一定价值。     

Region-related modular nerve-dependent motor activity in anorectum--cholinergic and nitrergic contribution to rat model

Disturbances of enteric nerve-mediated anorectal evacuation mechanisms have medical and social impact. The study aimed at further eliciting the contribution of cholinergic and nitrergic neurotransmission systems to modular nerve networks in different regions of Wistar rat anorectum. Electrical field stimulation (EFS, 0.8 ms, 40 V, 2, 5 or 10 Hz, 20 s), computerized mechanographic on-line setup and drugs were used to evaluate the motor responses of isolated rings from circular muscle of rectum (proximal, middle, and distal part), internal anal sphincter, and anal canal. Twitch-like frequency-dependent contractions, more pronounced in rectal preparations, characterized the modular motor responses of rectal circular muscle rings and anal canal. Depending on the frequency of stimulation, the motor activity of internal anal sphincter varied from deep long-lasting relaxation to initial short-lasting relaxation, followed by a contraction. Electrically-evoked responses of anorectal preparations were tetrodotoxin (0.1 microM)-sensitive. In the presence of atropine (0.3 microM) the contractions of rectal rings decreased, relaxation of internal anal sphincter increased and inhibition of the contractions of the anal canal occurred, followed by relaxation. During atropine treatment, NG-nitro-L-arginine (0.5 microM) increased the contractile responses and suppressed internal anal sphincter relaxations. L-arginine (0.5 microM) decreased the contractions and extended the relaxations of internal anal sphincter and anal canal. Our results suggest that cholinergic and nitrergic systems are not equally involved in modular nerve networks of various regions of anorectum. Cholinergic transmission is more expressed in distal rectum, underlying its contractile potency, while nitric oxide-dependent transmission(s) control the relaxation ability of the internal anal sphincter and anal canal.     

直肠表面动脉分布与微血管构筑相关性的研究

目的:研究直肠与肛管器官表面动脉分布与器官内小微动脉及毛细血管精确分布间的对应关系.方法:20例成人标本行巨微解剖观察表面动脉分支分布特点;20例胎儿尸体,墨汁灌注,组织切片及揭层透明铺片,光镜观察器官内微血管的构筑情况,测量各部位毛细血管分布密度.结果:器官表面动脉在直肠和肛管呈区域性分布的特点,在上半直肠前壁和直肠颈及肛管后壁中线部位存在"无血管吻合区".微血管测量结果显示上半直肠前壁和直肠颈及肛管后壁中线部位,肌层、粘膜下层及粘膜层毛细血管密度均低于同层其他部位.结论:直肠与肛管表面动脉分布与器官内小微动脉及毛细血管精确分布间存在对应关系,临床可根据肉眼所见表面动脉分布来评估直肠和肛管血供.     

Cancer of the anal canal

Seventy-four carcinomas of the anal canal (4,9% of the total number of rectum carcinoma for 1952-1982) were studied, including 45 squamous-cell, 23 adenogenic and 6 undifferentiated carcinomas. Adenogenic carcinomas originated from the rectum mucous membrane over the serrated line; as distinct from carcinomas of other parts of the rectum the mucus-forming and poorly differentiated tumours were predominant among them. Squamous-cell carcinomas originated from the squamous epithelium of the lower part of the anal canal, from the transitional area and from the rectum mucous membrane over the serrated line. They were characterized by peculiarity of their histological structure: they included 11 basaloid carcinomas, 6 carcinomas resembling transitional-cell carcinoma of the urinary bladder, 12 carcinomas resembling carcinoma of the uterine cervix. The problems of the terminology, histogenesis, clinical course of the anal canal carcinoma are discussed.     

Morphology of the epithelium of the lower rectum and the anal canal in the adult human

The anal canal is an important body part clinically. However, there is no agreement about the epithelium of the anal canal, the anal transitional zone (ATZ) epithelium in particular. The aim of this study is to clarify the structure of the epithelium of the human lower rectum and anal canal. Intact rectum and anus obtained from patients who underwent surgery for rectal carcinoma were examined by light and scanning electron microscopy (LM and SEM). By LM, three types of epithelium were observed in the anal canal: simple columnar epithelium, stratified squamous epithelium, and stratified columnar epithelium. The lower rectum was composed of simple columnar epithelium. SEM findings showed stratified squamous epithelium that consisted of squamous cells with microridges, changing to simple columnar epithelium consisting of columnar cells with short microvilli at the anorectal line. LM and SEM observations in a one-to-one ratio revealed that the area of stratified columnar epithelium based on LM corresponded to the anal crypt and sinus. In conclusion, the epithelium of the human anal canal was fundamentally composed of simple columnar epithelium and stratified squamous epithelium. We found no evidence of the ATZ.     

Fecal incontinence. Studies on physiology,pathophysiology and surgical treatment

The thesis consists of ten previously published studies and a review. The physiological and pathophysiological mechanisms in fecal incontinence has been studied by anal manometry, both by standard static anal manometry and by a new method, dynamic anal manometry, where anal sphincter pressure can be measured during simultaneous opening and closing of the anal canal. Patients with fecal incontinence showed abnormal sphincter pressures more frequently when dynamic anal manometry was used compared to standard anal manometry. The physiology and pathophysiology of the rectum was studied using rectal compliance measurements. Patients with normal anorectal function had a large variation in rectal compliance. Patients with fecal incontinence had as a group, lower rectal compliance than continent patients. This may lead to increased frequency of incontinence episodes in patients with fecal incontinence. The relationship between idiopathic fecal incontinence and pudendal nerve terminal latency was studied in 178 patients. The far majority of patients had normal latencies, and there was no correlation between latency and anal manometry. In contrast to previous suggestions, idiopathic fecal incontinence does not seem to be caused by pudendal nerve damage. Reconstruction of the external anal sphincter in patients with fecal incontinence due to obstetric sphincter lesion showed a poorer functional result among patients older than forty years compared to younger. This indicates that the general muscular weakening with age contribute to the incontinence in these patients. The treatment of more complicated forms of fecal incontinence consists of, apart from conservative treatment or colostomi, mainly in muscle transpositions or artificial anal sphincter. Transposition of the distal part of the gluteus maximus muscle to encircle the anal canal, did not lead to acceptable continence in any of the patients studied. Transposition of the gracilis muscle lead to acceptable continence in half the patients. Patients where the transposed muscle were stimulated by a neurostimulator had satisfactory continence in most cases. However, with this method several re-operations were necessary in some patients. In addition, some patients developed severe evacuation difficulties. Implantation of an artificial sphincter resulted in long-term improvement of continence in that half of patients in whom the artificial sphincter remained implanted. The other half of the patients had the artificial sphincter explanted due to various reasons, most frequently due to infection around the device. In selected patients with more complicated fecal incontinence, stimulated gracilis transposition or implantation of an artificial anal sphincter may be offered as an alternative to colostomy. Sacral nerve stimulation is a new method which seems to provide the best results among the more advanced procedures. Its minimally invasive character also contribute to the increasing use of this method in the last few years. Evaluation and treatment of fecal incontinence is presently in a state of rapid change with focus on more elaborate investigative methods and more diversified treatment.     

先天性巨结肠Ⅰ期经肛门术后肛肠功能评估

目的探讨先天性巨结肠I期经肛门术后患儿的排便功能、结肠和肛门括约肌功能。方法对I期经肛门术后5～9年的89例先天性巨结肠患儿进行排便功能问卷调查,同时对来院随访的58例患儿进行肛门直肠测压和钡灌肠检查,评价其术后肛肠功能。结果 89例先天性巨结肠术后患儿中,72例排便功能良好,排便次数1～2次/d,仅6例3～4次/d,7例稀便时污便,1例经常污便;3例便秘。89例患儿均有便意无便失禁。直肠肛门测压结果：2例患儿术后直肠肛管反射弱阳性;污便组肛管静息压较无症状组及对照组显著降低[（29.4±3.2）mmHg vs（40.2±5.1）mmHg vs（36.9±2.6）mmHg,P〈0.05,P〈0.05）],而直肠静息压显著增高[（65.9±7.2）mmHg vs（25.7±4.1）mmHg vs（11.0±1.3）mmHg,P〈0.05,P〈0.05）];污便组肛管收缩压明显低于无症状组及对照组[（183.5±15.6）mmHg vs（210.2±18.3）mmHg vs（200.6±13.8）mmHg,P〈0.01];而持续缩榨时间三组间差异无统计学意义。便秘组与其他三组间比较差异无统计学意义,且有1例出现括约肌反常运动。钡灌肠结果：先天性巨结肠术后所有患儿的结肠形态恢复良好,结肠框基本正常,未见到明显的痉挛段、移行段和扩张段,乙状结肠迂曲减少或消失,与术中切除肠管长度相符。先天性巨结肠术后所有病例的直肠肛管角比对照组明显增大（121.6°±14.2°vs 82.0°±11.4°,P〈0.01）,污便组又较便秘组及无症状组明显增大（138.4°±16.8°vs 106.3°±13.8°vs 110.6°±15.2°,P〈0.05）。结论先天性巨结肠I期经肛门术后患儿多数排便功能良好,结肠形态及肛门括约肌功能恢复良好,少数患儿污便可能与拖出结肠储便功能代偿不全、乙状结肠迂曲减少或消失、肛门括约肌损伤等有关。     

Reflex responses of neurons in the inferior mesenteric ganglion to mechanical stimulation of the colon, rectum, anal canal, and urinary bladder in the dog

Unitary discharges were recorded from the inferior mesenteric ganglion of decerebrate dogs. Eighty-one units were identified as sympathetic postganglionic neurons innervating the colon and rectum by collision test performed by stimulation of the lumbar colonic nerve. Discharges of four units were enhanced simultaneously with an increased outflow of the renal nerve by pinching a toe. Thus, those units were regarded as vasoconstrictors of colonic blood vessels. Sixty-five units whose discharges were depressed or not affected by the pinching were regarded as neurons innervating colonic smooth muscle or mucosa (colonic units). Discharges were enhanced in the majority of the colonic units by colonic, rectal, and vesical distension, and mechanical stimulation of the anal canal, while discharges were depressed in a few units by rectal and vesical distension, and the anal canal stimulation. The number and percentage of the depressed units increased not only after cutting the hypogastric nerves and descending branches of the lumbar colonic nerve but also after transection of the caudal pons. The reflex depressions disappeared after transection at the bulbospinal junction, but the reflex enhancements remained. These results indicate that the colonic units are enhanced through a spinal reflex by the inflows from the distal colon, rectum, anal canal, and urinary bladder through the lumbar colonic, hypogastric, pelvic, and pudendal nerves, while a few are inhibited through a supraspinal reflex by inflows through the pelvic and pudendal nerves.     

Effect of electronic toilet system (bidet) on anorectal pressure in normal healthy volunteers: influence of different types of water stream and temperature

Although bidets are widely used in Korea, its effects on anorectal pressures have not been studied in detail in terms of the water settings used. Twenty healthy volunteers were placed on a toilet equipped with a bidet, and anorectal pressures were measured with a manometry catheter inserted into the rectum and anal canal before and after using the bidet at different water forces (40, 80, 160, 200 mN), temperatures (24°C vs 38°C), and water jet widths (narrow vs wide). The pressure at anal high pressure zone decreased from 96.1 ± 22.5 to 81.9 ± 23.3 mmHg at water jet pressure of 40 mN and 38°C wide water jet (P < 0.001), from 94.3 ± 22.4 to 80.0 ± 24.1 mmHg at water jet pressure of 80 mN and 38°C narrow water jet (P < 0.001), and from 92.3 ± 22.4 to 79.6 ± 24.7 mmHg at a water jet pressure of 80 mN and 38°C wide water jet (P < 0.001). At other settings, no significant changes were observed. Our results indicate that, in addition to cleansing effect, bidet could be used to reduce anal resting pressure in the same manner as the traditional warm sitz bath under the conditions of low or medium water jet pressure, a warm water temperature, and a wide type water jet.     

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

In the intersphincteric space of the anal canal, nerves are thought to “change” from autonomic to somatic at the level of the squamous‐columnar epithelial junction of the anal canal. To compare the nerve configuration in the intersphincteric space with the configuration in adjacent areas of the human rectum, we immunohistochemically assessed tissue samples from 12 donated cadavers, using antibodies to S100, neuronal nitric oxide synthase (nNOS), and tyrosine hydroxylase (TH). Antibody to S100 revealed a clear difference in intramuscular nerve distribution patterns between the circular and longitudinal muscle layers of the most inferior part of the rectum, with the former having a plexus‐like configuration, while the latter contained short, longitudinally running nerves. Most of the intramural ganglion cells in the anal canal were restricted to above the epithelial junction, but some were located just below that level. Near or at the level of the epithelial junction, the nerves along the rectal adventitia and Auerbach's nerve plexus joined to form intersphincteric nerves, with all these nerves containing both nNOS‐positive parasympathetic and TH‐positive sympathetic nerve fibers. Thus, it was histologically difficult to distinguish somatic intersphincteric nerves from the autonomic Auerbach's plexus. In the intersphincteric space, the autonomic nerve elements with intrapelvic courses seemed to “borrow” a nerve pathway in the peripheral branches of the pudendal nerve. Injury to the intersphincteric nerve during surgery may result in loss of innervation in the major part of the internal anal sphincter. Clin. Anat. 26:843–854, 2013. © 2013 Wiley Periodicals, Inc.     

Pressure/flow relation in the peripheral pulmonary vascular bed in dogs: a preliminary study.

In order to test a technique for the determination of the pressure/flow relationship in the peripheral pulmonary vascular bed, the perfusion pressure changes with increasing and then decreasing flow in a small part of the lung (around 1 ml) were studied in anaesthetized supine dogs, after insertion of a specially designed double distal lumen Swan-Ganz catheter. One lumen was used for the pressure measurement, one for infusion of saline by a pump with variable flow, from 0.1 to 1.0 ml s-1. A conventional thermodilution Swan-Ganz catheter was also advanced in the pulmonary artery, to measure pressures in the pulmonary circulation as well as cardiac output. During infusion in the wedged catheter, right atrial, pulmonary arterial and balloon occlusion wedge pressures did not change. The pressure/flow curve of the occluded vascular bed showed a shape similar to that of collapsible tubes, with a pressure plateau at high flow, but this could also be due to vascular recruitment. The curve exhibited hysteresis, with a lower pressure when flow decreased. The slope of the initial part of the curve increased, on average, from 54 +/- 9 during normoxia to 91 +/- 27 mmHg s ml-1 during hypoxia (FIO2 = 0.10); this difference was not significant, but the perfusion pressure at high flow was significantly higher during hypoxia (P less than 0.05). Using blood instead of saline would allow the determination of the peripheral pulmonary vascular resistance under physiological conditions, and further work is needed to estimate the sensitivity and the reproducibility of this technique.     

The sympathetic innervation of the internal anal sphincter and rectum in the cat

The distribution of the sympathetic innervation to the internal anal sphincter (IAS) and rectum and the occurrence of different types of adrenergic receptors in the two organs were investigated in anaesthetized cats. Anal pressure and rectal motility were recorded by a manometric and a volumetric method respectively. Division of both the hypogastric nerves (HGN) and the lumbar colonic nerves (LCN) reduced the anal pressure by 46 +/- 6% of the resting pressure (40.9 +/- 6.4 mmHg) and consistently increased rectal motility. Efferent electrical stimulation of the HGN as well as the LCN elicited a contraction in the anus and the rectum, which, at maximal stimulation, caused the anal pressure to reach a similar level to that recorded before division of these nerves. After injection of phentolamine the anal contraction was abolished, whereas the rectal contraction was either abolished or converted to a beta-adrenergic relaxation. Propranolol caused increased rectal contraction in response to stimulation of the HGN and the LCN, whereas the anal contraction was unaffected. The results imply that the sympathetic nerves exert a tonic excitatory effect on the IAS and a dual effect on the rectum in the cat. The results also indicate that sympathetic fibres to the IAS are conveyed in both the HGN and the LCN. Inhibitory beta-adrenergic receptors seem to be of minor importance in regulating anal pressure.     

生物反馈式人工肛门感知系统的研制及效果

背景：人工肛门为治疗肛门失禁开辟了一条新的思路,然而现有的人工肛门没有感知和反馈功能。患者只能通过习惯而不是肠内容物的实际情况排便。因此人工肛门感知和反馈系统的研制是亟待解决的问题。 目的：研制能感知和反馈肠内容物量和压力变化的人工肛门感知系统。 方法：通过实验分别向20只新西兰兔近结肠远端10 cm肠管内注入不同体积的模拟气体、液体、半流体、固体肠内容物,并测量肠管和压力感应套囊的压力变化,分析4种状态肠内容物体积与肠管压力和压力感应套囊压力的关系。 结果与结论：实验结果表明,肠管内压力和套囊压力随肠内容物体积的增加而增大,套囊压力与肠内容物体积和肠管压力在一定范围内成正相关。通过实验证实,该生物反馈式人工肛门感知系统能有效的反映肠内容物的多少和肠内压的变化,是解决人工肛门感知和反馈的有效策略,为生物反馈式智能人工肛门的研制打下基础。     

腹腔镜下改良Soave巨结肠根治术后排便功能评价

目的评价婴幼儿先天性巨结肠行腹腔镜下改良Soave巨结肠根治术后的排便控制功能。方法2003年2月￣2006年3月行腹腔镜下改良Soave巨结肠根治术25例,年龄为3.5个月～4岁,平均年龄13.1个月。术后定期随访,随访时间为1～4年,平均2.5年。对患儿的排便控制能力、便秘、小肠结肠炎的发生率进行评价,术后1年行钡剂灌肠及直肠肛管测压检查。结果获访21例,根据李氏评分标准,排便功能优者(6￣5分)14例,良者(4￣3分)7例,无"差"者病例,便秘1例,小肠结肠炎2例。钡剂灌肠检查发现结肠扩张段、痉挛段消失,肛管直肠角度正常。直肠肛管测压检查均未出现直肠肛管抑制性反射。结论应用腹腔镜下改良Soave巨结肠根治术治疗婴幼儿先天性巨结肠,术后可获得良好的排便控制功能。     

Research on a novel artificial anal sphincter for human incontinence

This paper discusses a novel artificial anal sphincter with sensor feedback for controlling anal incontinence. The artificial anal sphincter system is a novel hydraulic-electric muscle which mainly comprises an artificial anal sphincter, a wireless power supply subsystem, and a communication subsystem. High integration of all functional components and no wire linking to the outer device make surgical implantation easier and lower risk. The wireless power supply subsystem employs a Class-E power amplifier based on adaptive control technique, and the electromagnetic compatibility in biological tissue is analysed. With the goal of designing a reliable and safe instrument, the models of human colonic blood flow and rectum motion are developed, the biomechanical material properties of human rectum and tissue ischaemia are analysed. The results show that the deformation of the artificial anal sphincter can be controlled by the press of reservoir below the upper limit of human tissue ischaemia. In vitro experiments demonstrate the artificial anal sphincter system is a good cure for human anal incontinence problems.     

Pressure/flow relation in the peripheral pulmonary vascular bed in dogs: a preliminary study

In order to test a technique for the determination of the pressure/flow relationship in the peripheral pulmonary vascular bed, the perfusion pressure changes with increasing and then decreasing flow in a small part of the lung (around 1 ml) were studied in anaesthetized supine dogs, after insertion of a specially designed double distal lumen Swan–Ganz catheter. One lumen was used for the pressure measurement, one for infusion of saline by a pump with variable flow, from 0.1 to 1.0 ml s^-1. A conventional thermodilution Swan–Ganz catheter was also advanced in the pulmonary artery, to measure pressures in the pulmonary circulation as well as cardiac output. During infusion in the wedged catheter, right atrial, pulmonary arterial and balloon occlusion wedge pressures did not change. The pressure/flow curve of the occluded vascular bed showed a shape similar to that of collapsible tubes, with a pressure plateau at high flow, but this could also be due to vascular recruitment. The curve exhibited hysteresis, with a lower pressure when flow decreased. The slope of the initial part of the curve increased, on average, from 54±9 during normoxia to 91±27 mmHg s ml^-1during hypoxia (FIO₂= 0.10); this difference was not significant, but the perfusion pressure at high flow was significantly higher during hypoxia (P < 0.05). Using blood instead of saline would allow the determination of the peripheral pulmonary vascular resistance under physiological conditions, and further work is needed to estimate the sensitivity and the reproducibility of this technique.     

Extensive colonic stricture due to pelvic actinomycosis.

A 36-year-old woman presented with a palpable tender mass at the left lower quadrant of the abdomen. She had suffered from constipation for five years and had a previous history of intrauterine device-use for one year. Preoperative barium enema and abdominopelvic CT showed a compatible finding of rectosigmoid colon cancer or left ovary cancer. She underwent segmental resection of the sigmoid colon along with the removal of left distal ureter, left ovary and salpinx. Pathologic examination revealed actinomycotic abscesses containing sulfur granules. Thereafter, she took parenteral ampicillin (50mg/kg/day) for one month and oral amoxicillin (250mg, tid) for 2 months consecutively. The patient has no specific problems for 6 months after surgical resection and long-term antibiotic therapy. This report may be the first of intrauterine device-associated pelvic actinomycosis involving both sigmoid colon and rectum extensively.     

Histo-topographic study of the longitudinal anal muscle

The longitudinal anal muscle (LAM) has been described as a vertical layer of muscular tissue interposed between the circular layers of the internal (IAS) and external (EAS) anal sphincters. There is, however, no general agreement in the literature on its composition and attachments. The aim of this study was to investigate the histological structure, attachments, and topography of the LAM in order to evaluate its role in continence and defecation, thus enhancing knowledge of the surgical anatomy of this region. After in situ formalin fixation, the pelvic viscera were removed from eight male and eight female cadavers (age range: 52-72 years). Serial macrosections of the bladder base, lower rectum and anal canal, cervix and pelvic floor complex, cut in the transverse (six specimens) and coronal (six specimens) planes, underwent histological and immunohistochemical studies. Four specimens were studied using the E12 sheet plastination technique. The LAM was identified in 10/12 specimens (83%). Transverse and coronal sections made clear that it is a longitudinal layer of muscular tissue, marking the boundary between the internal and external anal sphincters. From the anorectal junction it extends along the anal canal, receives fibers from the innermost part of the puborectalis and the puboanalis muscles, and terminates with seven to nine fibro-elastic septa, which traverse the subcutaneous part of the external anal sphincter, reaching the perianal dermis. In the transverse plane, the mean thickness of the LAM was 1.68 +/- 0.27 mm. Immunohistochemical staining showed that the LAM consists of predominantly outer striated muscle fibers and smaller numbers of inner smooth muscle fibers, respectively coming from the levator ani muscle and from the longitudinal muscular layer of the rectum. The oblique fibers suggest that the LAM may represent the intermediate longitudinal course of small bridging muscle bundles going reciprocally from the striated EAS to the smooth IAS and vice versa. The spatial result is the helical course of striated and smooth muscle fibers between the EAS and IAS, which contribute not only to the narrowing but also to some shortening of the anal canal during sphincter contraction. Thus, rather than being a boundary, the LAM gives anatomical evidence of a functional connection between two muscle systems with different structures and topography.