A common pathophysiology for full thickness rectal prolapse, anterior mucosal prolapse and solitary rectal ulcer

Anorectal pressures at rest, during conscious contraction of the external sphincter, during serial distension of the rectum and during straining to inflate a balloon were measured in 56 patients (21 patients with full thickness rectal prolapse, 24 patients with anterior mucosal prolapse, 11 patients with solitary rectal ulcer) and in 30 normal subjects. Both basal and squeeze pressures were significantly lower in the three groups of patients compared with matched normal controls (P less than 0.05). During increases in intra-abdominal pressure, anal pressure remained above maximum rectal pressure (P less than 0.05) in normal controls, with the highest anal pressures being recorded in the most caudal anal channels. In contrast, anal pressures tended to be lower than rectal pressures during this manoeuvre in patients with rectal prolapse, anterior mucosal prolapse and solitary rectal ulcer, and the highest pressures were recorded in the channels nearest the rectum. During serial distension of the rectum, 64 per cent of patients with solitary rectal ulcer, 75 per cent with anterior mucosal prolapse and 76 per cent with rectal prolapse, but only 10 per cent of controls, showed repetitive rectal contractions. The highest anal pressure always remained higher than rectal pressure during rectal distension in normal subjects (P less than 0.05) but not in patients. The threshold rectal volume required to cause a desire to defaecate and the maximum tolerable volume were significantly lower (P less than 0.05) in each of the patient groups, compared with normal subjects. The similarity in the results from patients with rectal prolapse, anterior mucosal prolapse and solitary rectal ulcer support the hypothesis that they share a common pathophysiology. In each of the groups, the rectum is hypersensitive and hyper-reactive, and weakness of the anal sphincter creates the conditions for prolapse of the rectum to occur into or through the anal canal.     

Effect of anterior resection on anal sphincter function

Minor difficulties with continence may occur after low anterior resection. Intraoperative injury to the internal anal sphincter or its nerve supply may contribute to this. To study the effect of low anterior resection on the anal sphincter mechanism, anal manometry was performed on 20 patients before and 10 days after resection. Fifteen patients were studied again 6 months after operation. Resting, maximum squeeze and squeeze increment pressures were recorded. Intraoperative manometry (n = 11) and presacral nerve stimulation (n = 6) were performed to determine whether peroperative injury to the internal anal sphincter had occurred. Resting and maximum squeeze anal canal pressures were reduced by low anterior resection, and did not recover. The squeeze pressure increment did not change. Division of the inferior mesenteric artery, full mobilization of the rectum and mesorectum, and rectal transection did not affect resting anal pressure, which was reduced after EEA anastomosis (mean (s.e.m.) before, 40(5) mmHg; after, 27(4) mmHg; P less than 0.05, n = 5). Presacral nerve stimulation produced relaxation of the internal sphincter. Anal sphincter pressures are reduced after low anterior resection. The external anal sphincter and the nerve supply to the internal anal sphincter appear intact. A direct injury to the internal sphincter is postulated.     

Anorectal sampling: a comparison of normal and incontinent patients

It has been suggested that sampling of rectal contents by the anal canal may play a role in the continence mechanism. To investigate this concept we studied 18 patients with faecal incontinence and 18 age and sex matched controls. A microtransducer catheter was positioned so that pressures were recorded from the rectum, the junction of the upper and middle thirds of the anal canal and the lower anal canal. Recordings were taken at rest and while distending the rectum with air in a balloon, and then with air injected freely into the rectum. Sampling (equalization of the rectal and upper anal canal pressures) was seen to occur spontaneously in 16 of the controls and only 6 of the incontinent group (P less than 0.02) and induced sampling occurred at a higher rectal volume in the incontinent group than in controls for freely injected air (P less than 0.002). Defective anorectal sampling may be an important contributory factor in the pathogenesis of anorectal incontinence.     

Anal continence following surgery for imperforate anus

Measurements of force in the anal canal, electrical activity of the smooth muscle of the internal sphincter, and the response to rectal distension, as well as subjective assessment of continence, have been made on a series of children operated upon for imperforate anus between 1955 and 1965.The most useful objective measurement appeared to be the reflex response in the anal canal on rectal distension. When a normal response occurred, good or moderate continence was observed. Poor continence was associated with a rise in anal canal force.The force in the anal canal on voluntary squeezing proved to be less informative in assessing continence than did the presence of a palpable puborectalis.     

Preliminary Study of a Novel Puborectalis‐Like Artificial Anal Sphincter

Artificial anal sphincter (AAS) is an in situ implanted device that acts as a treatment for fecal incontinence regardless of etiology by augmenting the incompetent sphincteric structures. However, AAS is impeded from becoming a valid therapy by its high rate of ischemic complication and malfunction. This article presents an original puborectalis‐like artificial anal sphincter (PAAS) that features a low risk of ischemia necrosis and rectal perception remodeling. The device retains continence by reproducing the action, including the pulling and angulating the rectum, of the puborectalis muscle, which forms the anorectal angle and reduces the required clamping pressure. Three rectal pressure sensors were embedded to maintain the pressure exerted on the rectal wall in a safe range and to monitor the distention of the rectum. A series of in vitro studies were conducted with a porcine rectum, and this PAAS prototype manifested the ability of maintaining continence with a clamping pressure considerably lower than that required by other AAS devices. The pressure sensors exhibit good linearity, and the function of rectal perception remodeling has also revealed high reliability with a success rate of 93.3%.     

Anorectal three-dimensional endosonography and anal manometry in assessing anterior rectocele in women: a new pathogenesis concept and the basic surgical principle

OBJECTIVE: The anatomy of the anal canal, the anorectal junction and the lower rectum was studied with 3-D ultrasound. METHOD: Seventeen women with normal bowel transit, without rectocele (group 1) and 17 female patients with a large anterior rectocele (group 2) were examined with a B&K Medical Rawk. Mean age was 44.5 and 51.6 years respectively. In group 1, one (5.8%) patient was nuliparous, five (29.4%) had a caesarian section, 11 (64.7%) had a vaginal delivery while in group 2, two (11.7%) patients were nuliparous, four (23.5%) had a caesarian section and 11 (64.7%) had a vaginal delivery. Images were reconstructed in midline longitudinal (ML) and transverse (T) planes. The external (EAS) and internal (IAS) anal sphincters were measured in both projections. RESULTS: In the ML plane, the EAS length was longer in group 1 (1.94 cm vs 1.61 cm, P < 0.05), the gap length was shorter (1.54 cm vs 1.0 cm P < 0.01) and the wall thickness was shorter in group 2 (0.40 cm vs 0.50 cm P < 0.01). The IAS (0.18 cm vs 0.23 cm P < 0.01) and EAS thickness (0.68 cm vs 0.77 cm, P < 0.05) (left lateral of the posterior quadrant) was greater in group 2. In group 1, the anterior upper anal canal wall in normal females was an extension of the rectal wall and the circular muscle was thicker in the mid-anal canal to form the IAS. In group 2, however, the wall layers were not identified and the IAS was found to be more distal. The differences were not statistically significant in the anal canal resting and squeeze pressures in the two groups. CONCLUSION: Obstetric trauma does not seem to play any role in rectocele pathogenesis because the anal sphincter muscles are anatomically and functionally normal and rectocele is also present in nuliparous and in women with caesarian sections. It seems that it is associated with the absence of EAS and thinner IAS in the anterior upper anal canal. Herniation starts at the upper anal canal extending to the lower rectum in high or large rectoceles and maybe produced by rectal intussusception because of excessive and prolonged straining during defecation. In fact, the denomination 'rectocele' should be changed to 'anorectocele'.     

Gender differences in the longitudinal pressure profile of the anal canal related to anatomical structure as demonstrated on three-dimensional anal endosonography

BACKGROUND: Anal canal squeeze pressure is assumed to be due to external sphincter contraction, but the contribution of other muscles has not been explored. METHODS: Ten male and ten nulliparous female asymptomatic subjects had three-dimensional anal endosonography and manometry. Incremental squeeze pressures at 0. 5-cm intervals, expressed as a percentage of the maximum pressure recorded anywhere in the canal, were related to the following anatomical levels: puborectalis, overlap between external anal sphincter (EAS) and puborectalis, external and internal anal sphincters, and external anal sphincter only. Levels were determined by coronal and sagittal endosonographic reconstructions. RESULTS: Puborectalis was the same length in men and women (median 23.9 versus 27.1 mm) but represented a greater proportion of the anal canal in women (45 versus 61 per cent; P = 0.02). At the level of puborectalis alone, the pressure generated as a proportion of maximum anal canal pressure was 71 (range 32-100) per cent in men and 62 (range 32-100) per cent in women. At the level of the EAS alone, the pressure was 60 (4-98) per cent in men and 82 (41-100) per cent in women; where the external sphincter was overlapped by puborectalis, the pressure was 98 (60-100) per cent in men and 75 (47-100) per cent in women. CONCLUSION: Maximal anal canal squeeze pressure is found where the puborectalis overlaps the EAS. This segment represents a significant proportion of anal canal length in women.     

External and internal anal sphincter responses to rectal distension in normal subjects and in patients with idiopathic faecal incontinence

The responses of the external anal sphincter and the internal anal sphincter to rectal distension were studied in 18 female patients who had idiopathic faecal incontinence with perineal descent and 11 female control subjects, by measuring pressures at six sites within the anal canal and the electrical activity of the external sphincter. The pressure profile in the normal anal canal, at rest, was asymmetric with the highest pressure recorded in the outermost channels. Rectal distension caused a transient increase in the activity of the external sphincter, which was associated with an increase in anal pressure, particularly in the outermost two channels. This was followed by a symmetrical reduction in anal pressure throughout the anal canal, caused by relaxation of the internal sphincter and shortening of the high-pressure zone. Two patterns of response were observed in the patients with idiopathic incontinence. Twelve patients (group 1) showed normal anal relaxation, but the maximum anal pressures recorded during rectal distension or a conscious squeeze were abnormally low, suggesting weakness of the external anal sphincter. The remaining six subjects (group 2), who were older than the group 1 patients, had much lower resting pressures and showed only external sphincter contraction in response to rectal distension, with no obvious internal sphincter relaxation. However, the maximum pressures recorded during a conscious contraction of the external sphincter were lower in this group than in the normal control subjects. These results suggest that group 2 patients have impaired internal anal sphincter tone, as well as external anal sphincter weakness. This may explain why all except one of the group 2 patients, compared with only 17 per cent of group 1 patients, reported incontinence to both solids and liquids.     

Contribution of the pudendal nerve to sensation of the distal rectum

BACKGROUND: Anal and rectal sensory mechanisms and pudendal nerve function are important in the control of faecal continence. The contribution of the pudendal nerve to sensation of the distal rectum was investigated. METHODS: Heat thresholds in the anal canal, distal and mid rectum were measured using a specially designed thermoprobe. Rectal sensory threshold volumes were measured using the balloon distension method. Needle electrodes were inserted into the external anal sphincter. Pudendal nerve block was performed through a perineal approach, and completeness assessed by loss of electromyographic activity. Heat and rectal volume thresholds were measured again following unilateral and bilateral pudendal nerve block. RESULTS: The technique was successful in four of six volunteers. Bilateral pudendal nerve block produced complete anaesthesia to heat in the anal canal (P = 0.029), but had no effect on heat thresholds in the distal or mid rectum. Rectal sensory threshold volumes were also unaffected by pudendal nerve anaesthesia. CONCLUSION: Anal canal sensation is subserved by the pudendal nerve, but this nerve is not essential to nociceptive sensory mechanisms in the distal or mid rectum. The transition between visceral control mechanisms in the lower rectum and somatic mechanisms in the anal canal may have functional importance in the initiation of defaecation and the maintenance of continence.     

肛门直肠畸形术后排粪失禁患儿盆腔磁共振成像表现及其临床意义

目的通过肛门直肠畸形术后排粪失禁患儿的盆腔MRI表现,了解盆底肌的形态,直肠、肛管的形态和位置,以及脊髓和骶骨的发育,为分析排粪失禁的原因及制订治疗方案提供客观依据。方法回顾性分析2009年9月至2011年12月间山东大学第二医院收治的34例肛门直肠畸形术后排粪失禁患儿的临床和影像资料,其中男2l例,女13例,年龄3,14岁。应用1．5TMR扫描仪,常规行轴位、冠状位及矢状位扫描,观察肛门括约肌、耻骨直肠肌和提肛肌、直肠、肛管的形态,以及脊髓、骶骨的发育情况。结果MRI检查提示：肛门外括约肌发育不良18例,耻骨直肠肌发育不良23例,肛提肌发育不良27例;直肠位置异常6例,直肠扩张12例,肛直角增大11例;肛管周围脂肪组织5例;合并神经管闭合不全2例,Currarino综合征2例,骶骨发育不全11例,直肠尿道瘘2例。以上影像学结果均经临床最终证实。结论MRI可清楚显示肛门外括约肌、耻骨直肠肌和肛提肌的形态,以及直肠和肛管的形态和位置,同时还可显示脊髓和骶骨的发育情况,是评价肛门直肠畸形术后排粪失禁患儿非常有价值的检查方法。     

Cerebral representation of the anorectum using functional magnetic resonance imaging

BACKGROUND: Anorectal continence depends not only on the organs of continence but also on cerebral control. There are relatively few data regarding cerebral processing of anorectal continence. METHODS: Thirteen healthy subjects underwent rectal distension to cause urge increasing to discomfort during functional magnetic resonance imaging (fMRI). In addition, a painful heat stimulus was applied to the skin of the anterior abdominal wall in the dermatome corresponding to the rectum. Voluntary contraction of the anal sphincter was also performed. Subjective rating of stimulus intensity was recorded. Evaluation of the data used a general linear model with Brain Voyager(trade mark). RESULTS: Subjective sensation of discomfort increased during repeated rectal distension and caused activation in the anterior cingulate gyrus, insula, thalamus and secondary somatosensory cortex seen on fMRI. Perception of rectal urge and discomfort activated the same cerebral regions with differing intensity. Application of a painful thermal stimulus in the corresponding dermatome showed a modification of the response. Voluntary contraction of the anal sphincter led to activation of the motor cortex and increased activity in the supplementary motor cortex and the insula. CONCLUSION: Cerebral representation of the anorectum as mapped by fMRI is intricate and reflects the complexity of the continence mechanism.     

Postanal repair for neuropathic faecal incontinence: correlation of clinical result and anal canal pressures

Neuropathic faecal incontinence is associated with low anal pressures and shortening of the anal canal. The operation of postanal repair has been shown to result in the return of acceptable continence in over 80 per cent of such patients. This paper examines the effect of the operation on anal canal pressures. Forty-two patients with primary faecal incontinence and electrophysiological evidence of neuropathy affecting the external anal sphincter and pelvic floor musculature were studied. Anal pressures were measured before operation and not less than 1 month afterwards. Two groups were chosen according to the clinical result. Group 1 consisted of 34 patients who regained continence and group 2 comprised 8 patients judged as having had an unsatisfactory result. In group 1 there was an increase in anal canal length (1.4 +/- 0.2 cm, mean +/- s.e.m., paired t test, P less than 0.001), resting pressure (19 +/- 3 cm H2O, P less than 0.001) and voluntary contraction pressure (13 +/- 3 cm H2O, P less than 0.001). In group 2 there was some increase in anal canal length (1.0 +/- 0.2 cm P less than 0.01) but no increase in mean resting pressure or mean voluntary contraction pressure. The results show that postanal repair effectively lengthens the anal canal and increases anal pressures in patients with a successful clinical outcome.     

The role of pelvic floor denervation in the aetiology of idiopathic faecal incontinence

Weakness of the muscles of the pelvic floor and external anal sphincter may in theory be caused by a traction injury to the pelvic nerves incurred as a result of the excessive perineal descent that accompanies straining in the descending perineum syndrome (DPS). To investigate the role of this weakness in the aetiology of idiopathic faecal incontinence (IFI), measurements of perineal position, puborectalis mean fibre density (MFD), anal canal pressures, rectal sensation, capacity, and compliance were made in continent (DPS alone, n = 20) and incontinent (DPS + I, n = 19) patients with DPS, and a group of age and sex matched control subjects (n = 20). Perineal descent on straining was greater in DPS alone than in DPS + I. Puborectalis MFD was raised by similar degree in both DPS groups compared with the control subjects, and external anal sphincter function, assessed as voluntary squeeze pressure, was impaired by similar degree in DPS + I and DPS alone compared with the control subjects. Maximal basal anal canal pressure and rectal compliance were significantly reduced in DPS + I compared with DPS alone and the control subjects. Thus IFI did not result from progression of neurogenic muscle weakness, but occurred when there was also diminished internal anal sphincter tone and reduced rectal compliance.     

Pelvic floor physiology

Pelvic floor physiology is poorly understood. The funnel shape of the pelvic floor and anal canal is uniquely developed to provide discriminatory continence of gas, liquid, and solid. Proximally, the pelvic floor consists of the pubococcygeus and iliococcygeus muscles. Distally, the anal canal is surrounded by the internal and external sphincter muscles. The anorectal ring is situated between the proximal pelvic floor and the distal anal canal. It is the site of the puborectalis muscle, which is anatomically, neurologically, and functionally merged with the deep portion of the external sphincter muscle. It is at this site that unique forces act to create both a flutter valve and the anorectal angle with the flap valve. Extrinsic pressures at this level reinforce both the flap valve and the flutter valve. Intrinsic pressures are generated by all of the surrounding muscles to produce a high-pressure zone. These factors are critical, but many other factors, such as rectal capacity, compliance, colonic transit, motility, and sensory mechanisms, also interact in a complex way to provide normal continence and defecation. Not surprisingly, no single test allows a complete assessment of the interactions of all these factors. Nevertheless, analysis of components thought to be important in pelvic floor physiology has contributed significantly to the understanding of normal as well as abnormal physiology. Although clinical evaluation continues to be the cornerstone of the diagnosis of pelvic floor disorders, anorectal physiological testing has contributed significantly to our understanding of the dynamics of the pelvic floor. With the refinement of existing techniques and the addition of new investigative tools, it is anticipated that knowledge of pelvic floor physiology will continue to grow.     

Sensory discrimination and dynamic activity in the anorectum: evidence using a new ambulatory technique

The anal canal in health is extremely sensitive to thermal stimuli, If temperature sensation plays a part in sensory discrimination two conditions must be fulfilled: there must be a temperature gradient along the anorectum and rectal contents must be able to come into contact with the sensitive anal mucosa. In a study of 53 normal subjects we demonstrated this temperature gradient with a median temperature difference between the rectum and lower, mid and upper anal canal of 0.4, 0.2 and 0.1 degrees C respectively. The second condition was examined in 15 normal ambulatory subjects by measuring mid-anal sphincter (SP) and rectal pressures (RP) with a microtransducer catheter. The signals were digitalized and recorded in a portable electronic memory for later computer display, and analysis. Marked spontaneous sphincter relaxation resulting in equalization of RP and SP occurred 7 times per hour (1-4). The conscious sensation of the presence of flatus was associated with an SP reduction of 30 mmHg (20-50 mmHg) and an RP increase of 7 mmHg (0-15 mmHg), such that RP greater than or equal to SP in 80 per cent of 144 recorded events. Using this new technique we have demonstrated the highly dynamic nature of the anal sphincter. Several times an hour the sphincter relaxes with subsequent equalization of rectal and anal pressures, allowing entry of rectal contents into the anal canal so that its presence and nature can be determined.     

Technical tips for intersphincteric resection: how to take out the rectum

Intersphincteric resection (ISR) is an ideal technique that preserves the anus, regardless of whether the internal anal sphincter is removed. However, it is difficult to dissect the anterior wall of the rectum from the adjacent organs. We herein describe a safe and useful ISR technique which draws out the rectum through the anus. The intersphincteric space (ISS) between the internal and external anal sphincter muscles was first transabdominally dissected. Next, the transanal dissection was advanced into the ISS bilaterally from the posterior side without dissecting the anterior wall of the anal canal, and the sigmoid colon and rectum were drawn out through the anus. Dissection between the anterior wall of the rectum and prostate/vagina could be easily performed under direct vision. This technique enables the dissection without any risk of a positive surgical margin or unexpected bleeding, and avoids injury to adjacent organs. This technique seems to be a safe and useful dissection technique for approaching the anterior wall of the anal canal.     

Anal canal anatomy showed by three-dimensional anorectal ultrasonography

Background Demonstrate precisely the anatomic configuration of the anal canal and the length and thickness of the anal sphincters using three-dimensional (3-D) anorectal ultra-sonography in both genders. Methods Twelve normal volunteer males and 14 females, with a mean age of 52.4 and 50.3 years, respectively, were prospectively enrolled in this study. All individuals from both groups were submitted to anorectal ultra-sonography. The anal canal was analyzed, measuring the length and thickness of the external anal sphincter (EAE), internal anal sphincter (IAS), puborectalis muscle (PR) and the gap (distance from the anterior EAS to the anorectal junction) in the midline longitudinal (ML) and transverse (MT) planes, and the results were compared between quadrants and genders. Results The distribution of sphincter muscles is asymmetric in both genders. The anterior upper anal canal is an extension of the rectal wall with all layers clearly identified. The anterior IAS is formed in the distal upper anal canal and is significantly shorter in female than in male in all quadrants. The anterior IAS length is shorter than the posterior and lateral in both genders. The anterior EAS length is significantly shorter (2.2 cm) and the gap is longer (1.2 cm) in female than in male (3.4 cm) (0.7 cm) (p < 0.05), respectively. The posterior and lateral EAS-PR is significant longer in males (3.6 cm) (3.9 cm) than in females (3.2 cm) (3.5 cm) (p < 0.05), respectively. The lateral EAS-PR is significant longer than the posterior part in both genders. The anterior IAS is significantly thicker in males (0.19 cm) than in females (0.12 cm) (p = 0.04). Conclusion 3-D anal endosonography enabled measurement of the different anatomical structures of the anal canal and demonstrated its asymmetrical configuration. The shorter anterior EAS and IAS associated with a longer gap could justify the higher incidence of pelvic floor dysfunction in females, especially fecal incontinence and anorectocele with rectal intussusception.     

Preoperative MRI sphincter morphology and anal manometry: can they be markers of functional outcome following anterior resection for rectal cancer?

Aim Good functional outcome following anterior resection (AR) for rectal cancer is an important clinical goal, but its prediction has proven difficult. Assessments such as anal manometry have been advocated as a potential tool but functional anatomy as depicted on MRI has not been investigated. This study looked at whether sphincter complex measurements recorded from preoperative staging MRIs and preoperative anal manometry have any correlation with functional outcome. Method Consecutive patients with rectal adenocarcinoma underwent preoperative manometric assessment and MRI staging. MRIs were assessed with regard to anorectal angle, puborectalis thickness, canal length and external and internal anal sphincter thickness. Functional outcome was categorized into three groups according to the number of adverse postoperative symptoms (frequency, urgency, leakage, diarrhoea, use of pads, use of antidiarrhoeal medication): 0, 1 and ≥2. This was evaluated 1 year following surgery and 6 months following stoma reversal where applicable. Univariate analysis of an ordinal regression model was performed with significance at the 5% level. Results Thirty patients were assessed. No single preoperative manometric parameter proved significant (P > 0.05). Only puborectalis thickness showed a significant (P = 0.01) relationship with the number of adverse symptoms suffered postoperatively. On receiver operating characteristics analysis, a cut‐off value of 3.5 mm gave an optimal sensitivity of 0.5 (95% CI, 0.17–0.83) and specificity of 0.86 (95% CI, 0.64–0.96). Conclusions Measurements of the puborectalis thickness on preoperative staging MRIs for rectal cancer may help predict functional outcome following AR. Prospective assessment of larger numbers with a fully validated continence score are required to evaluate these findings further.     

Postoperative evaluation of fecal continence after sphincter-preserving operations for rectal cancer

Seventy-eight sphincter-preserving operations for rectal cancer were evaluated from the viewpoint of postoperative fecal continence. Operative procedures consisted of 39 anterior resections and 39 pull-through operations and Maunsell-Weir’s operation. Postoperative fecal continence was evaluated by questionnaires and anorectal examinations including (1) the distance from the anal verge to the anastomosis, (2) the length of sensation to light touch in the anal canal, (3) electromyography of the sphincter, (4) internal sphincter reflex (5) pressure profile of the anal canal, and (6) barium enema radiography. Patients’ evaluations of their continence were good when the distance of the anastomosis was over 5 cm from the anal verge, and mostly poor under 3 cm. Good or fair evaluations were obtained when the internal sphincter reflex or high pressure zone of the anal canal were preserved. Size of the reservoir was measured using a planimeter on the lateral view of the barium enema up to 6 cm from the upper margin of the anal canal. Good or fair evaluations were obtained when size was 20 cm².     

Physiologic basis of digital-rectal stimulation for bowel evacuation in patients with spinal cord injury: identification of an anorectal excitatory reflex

BACKGROUND AND PURPOSE: Although advances in rehabilitation practices, pharmacology, and surgery offer new bowel program alternatives, digital-rectal stimulation is still utilized to facilitate defecation in patients with spinal cord injury (SCI). We speculated that defecation induced by such a technique is mediated through a reflex mechanism. METHODS: The study comprised 18 healthy volunteers (10 men, 8 women, mean age 36.6 +/- 9.7 years) and 9 patients with SCI (6 men, 3 women, mean age 35.1 +/- 11.2 years). The anal canal was dilated by a balloon inflated in 2-mL increments to 10 mL, and rectal pressure response was then recorded. The test was repeated after separate block of the external and internal anal sphincters and after individual anesthetization of the anal canal and rectum. RESULTS: In normal subjects, the rectal pressure rose significantly (p < 0.01) with 2-mL inflation. Increases in anal dilatation effected further rectal pressure elevations (p < 0.001), although there were no significant differences among the 4-, 6-, and 10-mL distensions (p > 0.05). The rectal pressure rise occurred with external, but not with internal, sphincter paralysis. In the subjects with paraplegia, there was no rectal pressure response to the 2- and 4-mL anal dilatations, while the 6-, 8-, and 10-mL distensions effected significant pressure increases (p < 0.001, p < 0.001, p < 0.001, respectively) that did not differ significantly among the 3 distending volumes. Internal sphincter inhibition, in contrast to the external sphincter, produced no rectal pressure response. In both normal subjects and subjects with paraplegia, the rectal pressure response did not occur after individual anesthetization of the rectum and anal canal. CONCLUSIONS: Anal dilatation induces rectal contraction through stimulation of mechanoreceptors, possibly in the internal sphincter. Rectal contraction upon anal dilatation suggests a reflex relationship that was absent on individual anesthetization of the possible 2 arms of the reflex arc: anal canal and rectum. This relationship, which we term the "anorectal excitatory reflex," appears to be evoked on digital anal dilatation. The reflex might be of diagnostic significance in defecation disorders and has the potential to be used as an investigative tool.