The importance of the internal anal sphincter (IAS) in maintaining continence: anatomical, physiological and pharmacological considerations

Oscillating calcium signals in smooth muscle cells underlie the persistent basal tone of internal anal sphincter

A persistent basal tone in the internal anal sphincter (IAS) is essential for keeping the anal canal closed and fecal continence; its inhibition via the rectoanal inhibitory reflex (RAIR) is required for successful defecation. However, cellular signals underlying the IAS basal tone remain enigmatic. Here we report the origin and molecular mechanisms of calcium signals that control the IAS basal tone, using a combination approach including a novel IAS slice preparation that retains cell arrangement and architecture as in vivo, 2-photon imaging, and cell-specific gene-modified mice. We found that IAS smooth muscle cells generate two forms of contractions (i.e., phasic and sustained contraction) and Ca2+ signals (i.e., synchronized Ca2+ oscillations [SCaOs] and asynchronized Ca2+ oscillations [ACaOs]) that last for hours. RyRs, TMEM16A, L-type Ca2+ channels, and gap junctions are required for SCaOs, which account for phasic contraction and 75% of sustained contraction. Nevertheless, only RyRs are required for ACaOs, which contribute 25% of sustained contraction. Nitric oxide, the primary neurotransmitter mediating the RAIR, blocks both types of Ca2+ signals, leading to IAS's full relaxation. Our results show that the oscillating nature of Ca2+ signals generates and maintains the basal tone without causing cytotoxicity to IAS. Our study provides insight into fecal continence and normal defecation.

Revisiting an ancient treatment for transphincteric fistula-in-ano 'There is nothing new under the sun' Ecclesiastes 1v9

OBJECTIVE

The history of treatments for fistula-in-ano can be traced back to ancient times. Current treatment of transphincteric fistulae is controversial, with many options available. We reviewed the history of treatment using cutting setons and present our series of transphincteric fistulae in the light of the series in the literature.

DESIGN

Literature review and case series.

SETTING

Hospital based coloproctology service

PARTICIPANTS

140 consecutive patients presenting with fistula-in-ano were included.

MAIN OUTCOME MEASURES

The literature pertaining to treatment of transphincteric fistula was reviewed, along with the outcome of various treatment methods for this condition. Data were collected for 140 consecutive patients presenting with fistula- in-ano were assessed for fistula healing, recurrence and complications.

RESULTS

A total of 140 consecutive patients with fistula-in-ano were identified, of which 111 were cryptoglandular (79.3%). Eighty-one of these 111 were transphincteric (73.0%). At a median follow-up of 35 months (range, 2-83 months), 70 transphincteric fistulae had healed (86.4%), 10 were still undergoing treatment (12.3%) and one patient was lost to follow-up prior to treatment (1.2%). Two patients in this group required a stoma (2.5%), six patients developed recurrence (7.4%); three 'true' recurrences (3.7%). One (1.2%) developed a chronic fissure. There were no reported cases of incontinence.

CONCLUSIONS

The management of transphincteric fistula-in-ano is complex and controversial, for which no clear surgical procedure has gained acceptance as the gold standard. This study demonstrates that transphincteric fistulae can be successfully treated using cutting setons. A high healing rate (86.4%), low recurrence rate (7.4%) and a low complication rate (3.7%) are shown, which compares favourably with published rates over a long follow-up.

The effect of topical anal captopril on resting anal pressure in healthy volunteers: the first human pilot study

BACKGROUND

Previous laboratory studies have shown that angiotensin II is produced locally in the rat internal anal sphincter causing potent contraction. The aim of this first human study was to evaluate the safety and manometric effects of topical application of captopril (an ACE inhibitor) on the resting anal pressure in healthy adult volunteers.

METHODS

Ten volunteers, mean age 32.5 years (range, 19-48 years), underwent anorectal manometric evaluation of the mean anal resting pressure (MRAP) and the length of the high-pressure zone (HPZ) before 20 and 60 min after topical application of captopril (0.28 %) cream. Cardiovascular variables (systolic blood pressure, diastolic blood pressure and pulse) were measured before and for up to 1 h after cream application. Side effects were recorded. Adverse events and patient comfort after the cream application were evaluated within a 24-h period by completing a questionnaire.

RESULTS

There was no significant change overall in MRAP following captopril administration, although in half the patients, there were reductions in MRAP after treatment. Half the patients had a reduction in the mean resting HPZ length; however, there was no overall difference between pre- and post-treatment values. There was no effect on basic cardiovascular parameters and no correlation between manometric and cardiovascular variables.

CONCLUSIONS

Topical application of captopril cream may result in a reduction in MRAP in volunteers without anorectal disease. Its use is associated with minimal side effects. It may be a new potential therapeutic option in the treatment of anal fissure. Further studies are required to determine the optimal concentration, dose and frequency of application.

Anorectal function after partial intersphincteric resection in ultra-low rectal cancer

AIM

To investigate the feasibility and efficacy of intersphincteric resection (ISR), in terms of postoperative anorectal function, for ultra-low rectal cancer in mainland China.

METHOD

A total of 43 patients who consecutively underwent curative partial ISR for ultra-low rectal cancer between 2006 and 2009 were enrolled in the study. Defaecatory function was assessed, using detailed questionnaires, 3, 6 and 12 months after surgery. The Wexner score was used to assess faecal continence, and anal manometry studies were performed to analyse anal sphincter function.

RESULTS

Overall defaecatory function was assessed as being satisfactory in 41 of 43 patients. Twelve months after surgery, the mean Wexner score was 4.0 ± 3.6. Anal manometry studies showed a significant change at 3 months and further, gradual, improvement over the following year. During the postoperative period, maximum squeeze pressure reached a normal value of 174.1 ± 19.5 mmHg (P = 0.041) by 6 months and resting pressure was 42.4 ± 5.6 mmHg by 12 months, which was close to the preoperative level (P = 0.038).

CONCLUSION

Because of the satisfactory recovery of defaecatory function and good oncological results, partial ISR may be recommended as an effective sphincter-preserving operation for patients with ultra-low rectal cancer.

Should we care about the internal anal sphincter?

The internal anal sphincter is currently regarded as a significant contributor to continence function. Four physiological and morphological aspects of the internal anal sphincter are presented as part of the current evidence base for its preservation in anal surgery. 1) The incidence of continence disturbance following deliberate internal anal sphincterotomy is underestimated, although there is presently no prospective imaging or physiologic data supporting the selective use of sphincter-sparing surgical alternatives. 2) Given that the resting pressure is a measure of internal anal sphincter function, its physiologic representation (the rectoanal inhibitory reflex) shows inherent differences between incontinent and normal cohorts which suggest that internal anal sphincter properties act as a continence defense mechanism. 3) Anatomical differences in distal external anal sphincter overlap at the point of internal anal sphincter termination may preclude internal anal sphincter division in some patients where the distal anal canal will be unsupported following deliberate internal anal sphincterotomy. 4) internal anal sphincter-preservation techniques in fistula surgery may potentially safeguard postoperative function. Prospective, randomized trials using preoperative sphincter imaging and physiologic parameters of the rectoanal inhibitory reflex are required to shape surgical decision making in minor anorectal surgery in an effort to define whether alternatives to internal anal sphincter division lead to better functional outcomes.

Anorectal functional results after transanal endoscopic microsurgery in benign and early malignant tumors

BACKGROUND

Transanal endoscopic microsurgery (TEM) has been suggested as a minimally invasive procedure of low morbidity for rectal villous adenomas and early anorectal adenocarcinomas. It has been used clinically in many areas outside of China for more than 20 years, but it began in mainland China only about 2 years ago. Some articles have reported excellent results with regard to morbidity and relapse rate with TEM, but there are no studies addressing its functional results in China until now. The aim of the present study was to analyze the effect of TEM on the manometric results.

METHODS

Thirty-seven patients (16 females, 21 males) underwent TEM and were followed for more than 6 months. Anorectal manometry and an incontinence questionnaire were administered 1 week preoperatively, 2 weeks postoperatively, 3 and 6 months postoperatively.

RESULTS

Of the 37 patients, 24 had villous adenomas and 13 had adenocarcinomas (11 uT1 and 2 uT2). Anorectal manometric values showed the mean anal resting pressure (ARP) decrease from 45 +/- 6 mmHg to 29 +/- 4 mmHg (p < 0.05) and the maximum tolerable volume (MTV) decrease from 175 +/- 21 ml to 90 +/- 15 ml (p < 0.05) at the third month after TEM. Maximal squeeze pressure (MSP) decreased from 181 +/- 20 mmHg to 92 +/- 14 mmHg (p < 0.05) at second week after operation and returned to normal value by the third postoperative month. The ARP and MTV were 45 +/- 5 mmHg and 177 +/- 21 ml, respectively, at 6 months after TEM, near the normal value (p > 0.05). Rectoanal inhibitory reflex (RAIR) was absent preoperatively in two patients; it was also absent in 10 patients 3 months postoperatively and in three patients 6 months postoperatively. Endosonography demonstrated internal anal sphincter (IAS) rupture in five patients, and full integrity of the external anal sphincter (EAS) in all patients. Of the five patients with IAS rupture, four had temporary incontinence to flatus normalized up to three postoperative months. Most patients had more times of stools per day and relative higher Wexner scores in a short period after TEM. All these patients were followed for 6-20 months with no incidence of relapse.

CONCLUSIONS

Anorectal function was preserved well after TEM, although some anorectal manometric parameters changed over time. Thus TEM is safe, in terms of anorectal function, for the cure of benign and early malignant tumors of the rectum.

Rectoanal reflexes and sensorimotor response in rectal hyposensitivity

PURPOSE

Rectal hyposensitivity commonly causes anorectal disorders, but its underlying mechanism is unknown. We hypothesized that subjects with rectal hyposensitivity have altered rectoanal reflexes and/or sensorimotor response.

METHODS

We performed stepwise graded balloon distensions of the rectum in 30 subjects with constipation and rectal hyposensitivity and in 23 healthy controls. Thresholds for first sensation, desire, and urgency to defecate were assessed. The lowest balloon volume that evoked rectoanal inhibitory reflex, rectoanal contractile reflex, and sensorimotor response and manometric characteristics and rectal compliance were examined.

RESULTS

Reflex responses were present in all subjects. The balloon volumes were higher in subjects with rectal hyposensitivity for inducing rectoanal inhibitory reflex (P = .008) and contractile reflex (P = .001) compared with controls. All controls showed a sensorimotor response, but in 13 hyposensitive subjects (43%) the onset of sensorimotor response was associated with absent sensation and in 17 (57%), with a transient rectal sensation. Thresholds for eliciting sensorimotor response were similar between patients and controls, but the amplitude, duration, and magnitude of response were higher (P < .05) in patients. Rectal compliance was similar between controls and hyposensitive subjects with transient sensation but higher (P = .001) in subjects with absent sensation.

CONCLUSIONS

Constipated subjects with rectal hyposensitivity demonstrate higher thresholds for inducing rectoanal reflexes and abnormal characteristics of sensorimotor response. These findings suggest either disruption of afferent gut-brain pathways or rectal wall dysfunction. These altered features may play a role in the pathogenesis of bowel dysfunction in rectal hyposensitivity.

Mechanisms controlling normal defecation and the potential effects of spinal cord injury

Spinal cord injury frequently leads to bowel dysfunction with the result that emptying the bowel can occupy a significant part of the day and reduce the quality of life. This chapter contains an overview of the function and morphology of the normal distal gut in the human, and of gut behaviour in normal defecation. In humans, this can be monitored and is described, but knowledge of the mechanisms controlling it is limited. Work on animals has shown that the intrinsic activity of the smooth muscles and their interactions with the enteric nervous system can program the activity that is necessary to expel waste material, but the external anal sphincter is controlled through somatic nerves. The gut however also receives input from the central nervous system through autonomic nerves, and a spinal reflex centre exists. Voluntary effort to induce defecation can influence all the control mechanisms, but the precise importance of each is not understood. The behaviour and properties of the individual muscles in the normal human rectum and anal canal are described, including their responses to intrinsic nerve stimulation and adrenergic and cholinergic agonists. The effects of established spinal cord injury are then considered. For convenience, supraconal and conal/cauda equina lesions are considered as two categories. Prolongation of transit times and disordered defecation are common problems. Supraconal lesions result in reduced resting anal pressures and increased risk of fecal incontinence. The acute effects of spinal cord injury are described, with injury causing ileus (prolonged total gastrointestinal transit times), constipation (prolonged colonic transit times) and fecal incontinence (passive leakage).

Preliminary evaluation of an injectable anal sphincter bulking agent (Durasphere) in the management of faecal incontinence

BACKGROUND

It has been previously shown that 'bulking' of internal anal sphincter defects may provide an effective method to treat patients with faecal incontinence, but the benefit wears off with time.

AIM

To assess the efficacy of a larger molecule, bulking agent (Durasphere) over the short- and long-term in patients with an internal anal sphincter defect refractory to conservative management.

PATIENTS

Eighteen patients (nine male, nine female) with a mean age of 60 years were recruited. All patients had persistent faecal leakage/soiling.

METHODS

Durasphere was injected in the submucosal plane to restore anal canal symmetry. All patients had anorectal physiology, endoanal ultrasound, continence grading, patient satisfaction and quality of life scores assessed at 1, 3, 6 and 12 months.

RESULTS

The mean follow-up is 28.5 months. Changes from baseline were not statistically significant up to 6 months. At 12 months there was significant improvement in the continence grading (P=0.003), patient satisfaction (P=0.053) and all quality of life subscales: lifestyle (P=0.004), coping (P=0.011), depression (P=0.024) and embarrassment (P=0.059). Anorectal physiological parameters apart from the maximum tolerable rectal volume at 12 months (P=0.036) showed no significant improvement.

CONCLUSIONS

Anal sphincter bulking with Durasphere is safe and effective in the short term as well as the longer term. More importantly, there is no evidence of attenuation of effect over time.

Fecal incontinence after minor anorectal surgery

PURPOSE

Fecal leakage after open lateral internal anal sphincterotomy for chronic anal fissure is common, but underreported. The aim of this study was to prospectively assess the physiologic and morphologic effects of sphincterotomy, comparing continent and incontinent patients after surgery. This group was further compared with an unselected group of patients presenting with incontinence after hemorrhoidectomy.

METHODS

Between January 1997 and June 1999, 23 patients were prospectively followed up through internal sphincterotomy with conventional and vector volume anorectal manometry, parametric assessment of the rectoanal inhibitory reflex, and endoanal magnetic resonance imaging. Fourteen continent patients were compared with 9 incontinent postoperative cases, 9 patients referred with incontinence after hemorrhoidectomy, and 33 healthy volunteers without anorectal disease.

RESULTS

Significant differences were noted between continent and incontinent postsphincterotomy cases for all resting conventional and vector volume parameters and for some squeeze parameters. Although there was a significant reduction in postoperative high pressure zone length at rest, there were no differences between the postoperative groups. There was an increase in sphincter asymmetry of 6.7 percent (+/- 3.5 percent) in incontinent postsphincterotomy patients and a decrease of 2.8 percent (+/- 3.2 percent) in continent cases. Significant differences were noted for resting parameters between incontinent postsphincterotomy and posthemorrhoidectomy patients, with a higher resting sphincter asymmetry in the latter group. The area under the rectoanal inhibitory curve was smaller in postsphincterotomy incontinent patients when compared with continent cohorts over the distal and intermediate sphincter zones at rest with a reduced latency of inhibition. There was no difference in the magnetic resonance images of the sphincterotomy site between incontinent and continent postsphincterotomy cases and no posthemorrhoidectomy case had evidence of sphincteric damage.

CONCLUSION

There are complex significant differences in the postoperative physiology of patients undergoing lateral internal sphincterotomy who become incontinent when compared with those who maintain continence. These physiologic changes are not reflected in detectable morphologic sphincteric differences. It is unknown whether these changes predict for long-term incontinence, and it is suggested that postoperative incontinence after minor anorectal surgery is not necessarily related either to a preexisting sphincter defect or inadvertent intraoperative sphincter injury.