自制针状电极采集尿道外括约肌肌电图

尿道外括约肌肌电图是确定尿道肌肉神经支配是否存在异常的可靠检查项目。尿道外括约肌与肛门括约肌的神经支配基本相同,常通过作肛门括约肌肌电图的检查来判断尿道外括约肌的电活动。     

肌营养不良征的肌电图分析

目的：探讨肌营养不良肌患的神经电生理改变。方法：对16例肌营养不良患进行常规肌电图(EMG)、神经电图(ENOG)检测，EMG检测四肢近端肌肉及腓肠肌等，观察静息状态时自发电位，测定运动单位电位(MUP)的时限、波幅、大力收缩时的募集相。测定运动、感觉神经的传导速度(MCV、SCV)及动作电位的末端潜伏期(ML)诱发电位波幅。结果：本组资料显示所检肌时限异常率占82％，波幅降低率占72％，大力收缩早募集占60％。结论：肌电图检测可以对肌营养不良和脊肌萎缩症提供很好的诊断和鉴别诊断依据。     

皮肤交感反射、肛门括约肌肌电图和瞬目反射在帕金森病诊断中的应用

目的探讨皮肤交感反射(SSR)、肛门括约肌肌电图(EAS-EMG)和瞬目反射在帕金森病(PD)诊断中的应用价值。方法选择金华市中心医院收治的帕金森病患者50例,根据患者的神经功能评估情况,将其分为无自主神经功能障碍(PD-NAS)组(35例)和自主神经功能障碍(PD-AS)组(15例)。另选择50名同期健康体检者作为对照组。对两组进行帕金森病自主神经症状评分(SCOPA-AUT),同时检测两组的皮肤交感反射、肛门括约肌肌电图和瞬目反射情况,分析帕金森病自主神经症状评分与皮肤交感反射、瞬目反射和肛门括约肌肌电图之间的相关性。结果 PD-AS组SCOPA-AUT平均得分显著高于PD-NAS组(P0. 05),亦显著高于对照组(P0. 05)。PD-AS组患者皮肤交感反射(SSR)与对照组相比,潜伏期延长、波幅降低(P0. 05)。PD-AS组肛门括约肌轻微收缩时运动单位(MUAP)的平均时限和多相百分比与PD-NAS组相比显著提高(P0. 05)。PD-AS组较PD-NAS组瞬目反射R2、R2'波潜伏期延长(P0. 05)。PD-AS组上下肢SSR波幅与上下肢的SSR潜伏期呈正相关(P0. 05)。SCOPA-AUT得分与MUAP的平均时限和多相波百分比呈正相关(P0. 05)。结论皮肤交感反射、瞬目反射和肛门括约肌肌电图能够反应帕金森病患者自主神经功能障碍的严重程度,能够为帕金森病的早期诊断提供依据。     

如何将兔股薄肌转变为新肛门括约肌

如何将兔股薄肌转变为新肛门括约肌［英］ｓｈａｔａｒｉ　　Ｔ…／／ＡＳＡＩＯ．－１９９３，３９．－４８６为了重建大便失禁时的肛门括约肌，将股薄转移到肛管周围用电刺激维持收缩是一可行的方法。但快速收缩的股薄肌不可能长期收缩，并且在每次电刺激之间肌肉必须保...     

80例多发性肌炎、皮肌炎患者的肌电图研究

目的：探讨肌电图(EMG)、神经传导速度(NCV)的检测对提高多发性肌炎、皮肌炎的诊断价值。方法：分析80例多发性肌炎、皮肌炎患者肌电图检查中自发电活动,MUP时限、波幅及多相波,最大随意收缩时的募集形式,以及NCV检查及肌肉活检资料。结果：80例患者中65例EMG示肌原性损害,同时观察到15例患者出现NCV的轻度减慢(18．6%)、5例(6．3%)患者NCV远端潜伏期延长、21例(26．3%)患者出现复合肌动作电位波幅轻度下降。10例(12．5%)患者EMG、生化检查、肌肉活检正常,仅表现为MUP多相波增多,但追踪观察三个月后,其中6例患者EMG出现肌原性损害。结论：EMG、NCV测定和追踪监测是诊断多发性肌炎和皮肌炎的有价值的电生理检测方法。     

肌电生物反馈疗法联合综合康复训练对老年脑梗死偏瘫患者上肢运动功能的效果

目的 探讨肌电生物反馈疗法联合综合康复训练对老年脑梗死偏瘫患者上肢运动功能的疗效。方法 选择2021年1月至2021年12月九江市第一人民医院老年医学科收治的80例脑梗死后遗偏瘫的老年患者,性别不限,年龄60～80岁。按照入院先后顺序分为观察组和对照组,每组40例。对照组接受综合康复训练治疗,观察组在对照组的基础上加用肌电生物反馈疗法,比较两组系统康复治疗后三角肌、肱三头肌、前臂伸肌最大收缩时的肌电信号幅度水平、Fugl-Meyer上肢运动功能评分(FMA)与患肢活动度。结果 训练后,两组三角肌、肱三头肌、前臂伸肌最大收缩时的肌电图波幅、FMA评分及患肢的外展、外旋、内旋角度均较训练前升高(P<0.05),与对照组比较,观察组以上指标更高(P<0.001)。结论 对于老年脑梗死偏瘫患者的康复治疗,可在综合康复训练基础上加用肌电生物反馈疗法,能够更好地帮助患者重建上肢运动功能。     

骨间前神经卡压综合征的神经电生理分析

目的:探讨骨间前神经卡压综合征的神经电生理诊断方法.方法:对2008-2012年间17例临床初诊为骨间前神经卡压综合征患者进行正中神经运动传导功能、感觉传导功能检测及靶肌肉静息状态和重收缩时的肌电图检测.结果:所检17例患者的拇长屈肌、旋前方肌静息状态见自发电活动,重收缩募集反应减弱;而旋前圆肌、桡侧屈腕肌、拇短展肌静息状态下无自发电活动,重收缩募集反应为混合相;正中神经的运动神经传导、感觉神经传导的潜伏期(Lat)、神经传导速度(NCV)、复合肌肉动作电位(CMAP)、感觉神经动作电位(SNAP)波幅均在正常范围.结论:神经电生理检测对骨间前神经卡压综合征有重要的诊断及鉴别诊断价值,为临床诊断提供可靠依据.     

肯尼迪病患者的神经电生理分析

目的:研究肯尼迪病患者的神经电生理特点,提高对此病电生理的认识。方法:对经基因确诊的3例肯尼迪患者的神经电生理进行总结分析。3例患者均行神经传导和肌电图(EMG)检测。神经传导检查包括:正中神经、尺神经、腓总神经、胫神经和腓肠神经。检测项目包括运动神经潜伏期(Lat)、复合肌肉动作电位波幅(CMAP)、运动神经传导速度(MCV);感觉神经潜伏期(lat)、感觉神经动作电位波幅(SNAP)、感觉神经传导速度(SCV)。EMG:检查双侧舌肌、胸锁乳突肌、三角肌、第一骨间肌、胸椎旁肌、股四头肌、胫前肌。检测项目包括静止时的自发电位,轻收缩时运动单位动作电位(MUP)的时限、波幅,重收缩时的募集相。结果:第1例患者运动神经传导正常,感觉神经SNAP波幅低和SCV正常。第2例患者双正中神经运动Lat延长、CMAP下降,NCV减慢,双正中神经感觉未测及SNAP波幅,合并腕管综合征;其余运动神经传导正常,感觉神经SNAP波幅和SCV均低。第3例运动神经传导正常,感觉SNAP波幅低和SCV下降。本组3例患者EMG多块肌肉静息时出现2处以上的纤颤波、正尖波,轻收缩时MUP时限增宽,波幅增高,部分呈巨大电位,重收缩时呈单纯相或单纯混合相。结论:KD患者EMG呈广泛神经源性改变,可累及感觉。     

肩胛上神经卡压综合征的电生理诊断

目的：探讨肩胛上神经卡压综合征电生理诊断方法。方法：对10例肩胛上神经卡压综合征的病人应用肌电图（EMG）观察自发电位,检测肩胛上神经支配肌冈上肌、冈下肌;腋神经支配肌三角肌;肩胛背神经支配肌提肩胛肌的复合肌肉动作电位（CMAP）,观察指标为潜伏期、波幅的变化。结果：10例病人冈上肌均见自发电位,募集反应减弱,CMAP潜伏期延长,波幅降低,且波形离散。结论：电生理是诊断和鉴别诊断肩胛上神经卡压综合征的重要辅助手段。     

自体肌肉移植重建人工肛门括约肌

背景：有效的人工肛门括约肌重建能够改善肛门失禁患者的生存能力和生活质量。 目的：评价自体肌肉移植重建人工肛门括约肌的效果。 方法：分析自体臀大肌和股薄肌移植重建人工肛门括约肌的解剖学基础,并对应用自体臀大肌和股薄肌移植重建人工肛门括约肌的患者进行随访观察,通过评估人工肛门控便功能恢复情况以及相关并发症发生情况,明确自体臀大肌和股薄肌移植重建人工肛门括约肌的应用效果。 结果与结论：臀大肌和股薄肌均有丰富的血液供应,并且营养肌肉的动脉均有相应静脉和神经伴行。对应用自体臀大肌和股薄肌移植重建人工肛门括约肌的患者随访观察发现,患者多为直肠癌或者肛管癌,经过自体肌肉移植重建人工肛门括约肌后,均能获得较好的肛门排控便功能,较少发生肛门狭窄、肛周感染等并发症,无机体排斥反应的发生。     

External Anal Sphincter Response to Rectal Distention: Learned Response or Reflex

Three experiments were conducted to determine whether the external anal sphincter contraction which typically follows rectal distention is a reflex or a voluntary response. Experiment I compared 15 chronically constipated patients to 10 normal subjects. A reflex should be reliably elicited by its unconditional stimulus; but if this response is voluntary, chronically constipated patients would be less likely to show it because they have had fewer opportunities to practice it. Only half of chronically constipated patients showed the response compared to 100% of normals. Experiment II investigated whether the response is elicited by rectal distention during sleep in 10 healthy subjects. The response was significantly less likely to occur during sleep. Experiment III in 6 normal subjects revealed that this response can be voluntarily omitted. These experiments indicate that external anal sphincter contraction following rectal distention is a voluntary response, not a reflex.     

The probability of finding nerve branches to the external anal sphincter

Introduction  Normal defecation is a combination of several elements of reflex and voluntary functions. The issue of external anal sphincter innervation is of theoretical and clinical significance; however, literature on the subject is still scarce. Most study reports discuss the course of the pudendal nerve with no close insight into inferior rectal nerves supply to the external anal sphincter. We have not found any statistical “mapping” of the site of the nerve branches insertion into the external anal sphincter. Thus, the purpose of the present study was to determine the least and most typical location of nerve branches to the external anal sphincter. One hundred and ten pudendal nerve preparations were analysed. Following the dissection of the pudendal nerve and its branches, a beam compass was used to take linear measurements from the apex of the coccygeal bone to the point of nerve branch insertion to the external anal sphincter. The distance between coccygeal bone apex and the central tendon of the perineum was also measured. For the purpose of comparison, results are presented as relative Bi/A values. Computer programmes devised by the author of this paper within Turbo Pascal were then used to determine the probability of finding nerve branches to the external anal sphincter. Results  Based on the analysis of 110 preparations of the pudendal nerve and its branches, one might conclude that the former was the main although not necessarily the only source of external anal sphincter innervation. While analysing the most and the least probable location of nerve branches to the external anal sphincter, the muscle length was expressed as percentage, i.e., 0% of sphincter length = the apex of the coccygeal bone; 100% of sphincter length = the central tendon of the perineum. The length was then divided into 5% intervals with the probability of finding nerve branches determined by programmes written in Pascal. Within 30–85% of external anal sphincter length, the probability of finding nerve branches to the external anal sphincter is greater than 0.3 with peak probability of 0.68 in the interval between 55 and 65%. Discussion  Sphincter innervation and clinicoanatomical function of anal canal closure apparatus has been discussed with reference to external anal sphincter injury. Transcutaneous electrostimulation of the pudendal nerve and the use of anal canal electrodes have also been mentioned. Conclusions  The most probable location of nerve branches to the external anal sphincter is half way of its length, i.e., at hour 3 or 9 of the knee-elbow position or lithotomy position. The external anal sphincter can also be directly supplied by nerve branches originating from the sacral nerve root S4; the branches then go towards the posterior part of the sphincter.     

Increased anal basal pressure in chronic anal fissures may be caused by overreaction of the anal-external sphincter continence reflex

Chronic anal fissure is a painful disorder caused by linear ulcers in the distal anal mucosa. Even though it counts as one of the most common benign anorectal disorders, its precise etiology and pathophysiology remains unclear. Current thinking is that anal fissures are caused by anal trauma and pain, which leads to internal anal sphincter hypertonia. Increased anal basal pressure leads to diminished anodermal blood flow and local ischemia, which delays healing and leads to chronic anal fissure. The current treatment of choice for chronic anal fissure is either lateral internal sphincterotomy or botulinum toxin injections.In contrast to current thinking, we hypothesize that the external, rather than the internal, anal sphincter is responsible for increased anal basal pressure in patients suffering from chronic anal fissure. We think that damage to the anal mucosa leads to hypersensitivity of the contact receptors of the anal-external sphincter continence reflex, resulting in overreaction of the reflex. Overreaction causes spasm of the external anal sphincter. This in turn leads to increased anal basal pressure, diminished anodermal blood flow, and ischemia. Ischemia, finally, prevents the anal fissure from healing.Our hypothesis is supported by two findings. The first concerned a chronic anal fissure patient with increased anal basal pressure (170 mmHg) who had undergone lateral sphincterotomy. Directly after the operation, while the submucosal anesthetic was still active, basal anal pressure decreased to 80 mmHg. Seven hours after the operation, when the anesthetic had completely worn off, basal anal pressure increased again to 125 mmHg, even though the internal anal sphincter could no longer be responsible for the increase. Second, in contrast to previous studies, recent studies demonstrated that botulinum toxin influences external anal sphincter activity and, because it is a striated muscle relaxant, it seems reasonable to presume that it affects the striated external anal sphincter, rather than the smooth internal anal sphincter.If our hypothesis is proved correct, the treatment option of lateral internal sphincterotomy should be abandoned in patients suffering from chronic anal fissures, since it fails to eliminate the cause of high anal basal pressure. Additionally, lateral internal sphincterotomy may cause damage to the anal-external sphincter continence reflex, resulting in fecal incontinence. Instead, higher doses of botulinum toxin should be administered to those patients suffering from chronic anal fissure who appeared unresponsive to lower doses.     

Comparison of the contractile properties, oxidative capacities and fibre type profiles of the voluntary sphincters of continence in the rat

The external urethral sphincter (EUS) and external anal sphincter (EAS) are the principal voluntary striated muscles that sustain continence of urine and faeces. In light of their common embryological origin, shared tonic sphincteric action and synchronized electrical activity in vivo, it was expected that they would exhibit similar physiological and structural properties. However, the findings of this study using paired observations of both sphincters isolated from the rat show clearly that this is not the case. The anal sphincter is much more fatigable than the urethral sphincter. On completion of a fatigue protocol, the amplitude of the last twitch of the EAS had declined to 42 ± 3% of the first twitch, whereas the last twitch of the EUS was almost identical to that of the first (95 ± 3%). Immunocytochemical detection of myosin heavy‐chain isoforms showed that this difference was not due to the presence of more slow‐twitch oxidative type 1 fibres in the EUS compared with the EAS (areal densities 4 ± 1% and 5 ± 1%, respectively; P = 0.35). In addition, the fatigue difference was not explained by a greater contribution to force production by fast oxidative type 2A fibres in the urethral sphincter. In fact, the anal sphincter contained a higher areal density of type 2A fibres (56 ± 5% vs. 37 ± 4% in the EUS, P = 0.017). The higher oxidative capacity of the EUS, measured histochemically, explained its fatigue resistance. These results were surprising because the fatigue‐resistant urethral muscle exhibited faster single‐twitch contraction times compared with the anal sphincter (56 ± 0.87 ms vs. 72.5 ± 1.16 ms, P < 0.001). Neither sphincter expressed the type 2X myosin isoform but the fast‐twitch isoform type 2B was found exclusively in the EUS (areal density 16 ± 2%). The type 2B fibres of the EUS were small (diameter 19.5 ± 0.4 μm) in comparison to typical type 2B fibres of other muscles. As a whole the EUS is a more oxidative than glycolytic muscle. In conclusion, analysis of the twitch mechanics and fatigue of two sphincters showed that the EUS contained more fatigue‐resistant muscle fibres compared with the EAS.     

Oscillatory firing of single human sphincteric alpha 2 and alpha 3-motoneurons reflexly activated for the continence of urinary bladder and rectum. Restoration of bladder function in paraplegia

1. By recording with 2 pairs of wire electrodes from human sacral nerve roots (S3-S5) rhythmic as well as occasional firing was observed in alpha 2 and alpha 3-motoneurons in response to physiologic stimulation of the urinary bladder and the anal canal. The rhythmic firing consisted of periodically occurring impulse trains, most likely produced by true spinal oscillators which drove the motoneurons. 2. Alpha 2-motoneurons, innervating fast fatigue-resistant muscle fibres, were observed to fire with impulse trains of about 2 to 4 action potentials (Ap's). These impulse trains occurred every 110 to 170 msec (5-9 Hz). Alpha 3-motoneurons, innervating slow fatigue-resistant muscle fibres, fired about every 1400 msec (approximately 0.7 Hz) with impulse trains of about 11 to 60 Ap's. Alpha 1-motoneurons, innervating fast fatigue muscle fibres, and gamma-motoneurons were not observed in the continuous oscillatory firing mode. 3. Sphincteric motoneurons were observed most likely in the oscillatory firing mode in response to the sustained stretch (reflex) of the external and sphincter or to retrograde filling of the bladder (urethro-sphincteric guarding reflex), in order to preserve continence. A urethral sphincteric alpha 2-motoneuron increased its mean activity from 0.5 to 18 Ap's/sec during retrograde filling by changing its firing pattern from the occasional spike mode via the transient oscillatory firing mode to the continuous oscillatory mode. Up to a filling of the bladder of 500 ml the mean activity of the stretch receptors, measuring probably mural tension, increased roughly proportionally and the sphincteric motoneuron increased its activity to about 1 Ap/sec in the occasional spike mode. Up to 600 ml, the motoneuron responded in the transient oscillatory mode with mean activities of up to 5 Ap's/sec. With higher bladder fillings, the flow receptors afferents fired additionally, probably according to pressure symptoms, and the motoneuron switched into the continuous oscillatory firing mode and increased its activity up to 18 Ap's/sec at 700 ml. When the bladder was about 800 ml full, the stretch afferent activity decreased, the flow receptor activity increased strongly and the alpha 2-motoneuron activity decreased; the overflow incontinence had probably started. Micturition was not observed, probably because of brain death. 4. It is suggested that one adequate stimulus for an alpha 2-motoneuron of the external anal sphincter to jump into the oscillatory firing mode, was the activity from secondary spindle afferent (SP2) fibres from external anal sphincter muscle spindles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Excitability of the motor cortical representation of the external anal sphincter

This study was designed to assess the excitability of the motor cortical representation of the external anal sphincter by using transcranial magnetic stimulation (TMS). In six healthy volunteers, the rest motor threshold and the duration of the cortical silent period were determined with single TMS pulses, and the intracortical inhibition and facilitation were measured with paired TMS pulses. Values obtained from the anal sphincter were compared with those obtained from a muscle in the right hand. All subjects completed the study. Rest motor threshold and intracortical facilitation were similar in both muscles. In contrast, cortical silent period duration and intra-cortical inhibition were less for the anal sphincter than for hand muscle. This study has opened new perspectives for the investigation of anal sphincter cortical control in humans.     

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.     

The morphological differentiation of the internal sphincter muscle of the anus in the human embryo and fetus (26.01.1990)

Conclusion The opening of the anal canal appears to be the factor which initiated the differentiation of the sphincter apparatus.The internal sphincter m. of the anus is entirely composed of smooth muscle as distinct from the striated fibers of the m. puborectalis, and the external sphincter which is a mixture of smooth and striated fibers (of skeletal type). It develops in the terminal part of the internal circular layer of the rectal m., outside which are longitudinal fibers which descend early to form the external sphincter (beginning around the third month).This study shows that the internal sphincter is scarcely evident before 12 SA. Thus continence between 10 and 12 SA (after the closure of the anal membrane) is closely related to the other components of the sphincter apparatus. On the other hand, the internal sphincter has become well formed after 28 to 30 SA and then plays a direct role in maintaining continence.     

Membrane properties and the neuro-effector transmission of smooth muscle cells in the canine internal anal sphincter.

The most distal part of the circular muscle layer functions as the internal anal sphincter, which constitutes a high pressure zone at rest, but maintains a relaxed state during defecation. To elucidate such sphincter mechanisms of the smooth muscle cells, the circular muscle layer in the canine anal canal was examined within 2 cm from the anal verge. Both the mechanical and intracellular electrical activities were recorded simultaneously. The examined region could be divided into three different regions according to the pattern of spontaneous activity and innervation and consisted of an upper region (20-15 mm from the anal verge), a transitional region (15-5 mm from the anal verge) and a lower region (within 5 mm from the anal verge), respectively. The spontaneous membrane activity was characterized by ongoing slow potential changes and each potential change was associated with a phasic contraction in the three regions. The mean frequencies of spontaneous electrical activity were 6.8, 15.9, and 24.1 c/min in the upper, transitional and lower regions, respectively. In the transitional and lower region, muscle tone generation was observed. Transmural field stimulation (0.4 msec in pulse duration) evoked membrane depolarization and contractions in the lower region. The application of an alfa adrenergic blocking agent completely suppressed the generation of excitatory responses, leaving a long lasting hyperpolarization associated with relaxation. In the transitional and upper region, stimulation consistently evoked membrane hyperpolarization with relaxation. The characteristics of this hyperpolarization response varied among the three regions. The total duration of hyperpolarization increased distally, while the time to peak hyperpolarization became decreases in a reverse direction. These regional differences in the characteristics of spontaneous membrane activity and innervation indicate that the transitional and lower region might therefore function as the internal anal sphincter.     

Internal anal sphincter: an anatomic study

The anatomy of the internal anal sphincter and surrounding structures was investigated in 24 cadavers using a surgical microscope (6-25 x magnification). An understanding of the anatomy of the internal anal sphincter is helpful in avoiding complications during surgical procedures in the anorectal region. The external anal sphincter was composed of three ellipsoid rings of skeletal muscle (subcutaneous, superficial, and deep) that encircle the anal canal; in contrast, we found that the internal anal sphincter was composed of flat rings of smooth muscle bundles stacked one on top of the other, like the slats of a Venetian blind. In each anal canal, the average number of ring-like slats observed was 26.33 +/- 2.93 (range = 20-30) and each was covered by its own fascia. The smooth muscle fibers and fascia coalesced at three equidistant points around the anal canal to form three columns that extended distally into the lumen and differed in form from the other anal columns. When viewed from an anterior position, the columns were located anteriorly at the observer's right (5 o'clock position), posteriorly at the right (1 o'clock position), and laterally at the left (9 o'clock position). This heretofore unreported anatomy of the internal anal sphincter may play an important role in closing off the lumen of the anal canal and maintaining bowel continence.