Evaluation of the intrinsic innervation of the internal anal sphincter using electrical stimulation

A novel method for measurement of the recto-anal inhibitory reflex using anal acoustic reflectometry

AIM

The recto-anal inhibitory reflex (RAIR) is currently measured using manometry catheters, which potentially distort the anal canal. Anal acoustic reflectometry (AAR) is considered to be a catheter-free technique and primarily measures the function of the internal anal sphincter. We sought to determine if RAIR could be measured using AAR.

METHOD

Patients aged 18 and over attending the hospital for investigation of pelvic floor dysfunction were included. AAR parameters were obtained before (prerectal distension) and after (postrectal distension) inflation of a rectal balloon catheter with 100 ml of air. Minimum opening pressure (Op, cmH₂ O), opening elastance (Oe, cmH₂ O/mm² ), closing pressure (Cp, cmH₂ O), closing elastance (Ce, cmH₂ O/mm² ) and hysteresis (Hys, %) were recorded. The presence of RAIR was defined by a reduction of prerectal distension Op by 20% or more.

RESULTS

Thirty-two patients were included, 26 of whom were women. The mean age of patients was 57.5 years (SD 11.3 years). Nine patients had faecal incontinence, six patients had obstructive defaecation and 17 patients had both. RAIR was seen in 30/32 patients. The mean reduction in Op was 58.8% (range -59.18% to 100%). Three patients had 100% reduction. Comparison of pre- and post-RAIR parameters showed a significant difference in Op (34.44 vs 15.41, P < 0.0001), Oe (1.39 vs 1.1, P = 0.004), Cp (20.06 vs 8.00, P < 0.0001) and Ce (1.31 vs 1.13, P < 0.0001) but not Hys (39.71 vs 39.90, P = 0.88).

CONCLUSION

We describe a novel method for the measurement of RAIR. Rectal distension appears to alter resting pressure and the resistance of the anal canal to opening and closing, with complete inhibition of the sphincter complex in three patients.

Topographic and manometric characterization of the recto-anal inhibitory reflex

BACKGROUND

Recto-anal inhibitory reflex (RAIR) is an integral part of normal defecation. The physiologic characteristics of RAIR along anal length and anterior-posterior axis are unknown. The aim of this study was to perform topographic and vector-graphic evaluation of RAIR along anal canal using high definition manometry (HDM), and examine the role of various muscle components.

METHODS

Anorectal topography was assessed in 10 healthy volunteers using HDM probe with 256 sensors. Recto-anal inhibitory reflex data were analyzed every mm along the length of anal canal for topographic, baseline, residual, and plateau pressures during five mean volumes of balloon inflation (15 cc, 40 cc, 71 cc, 101 cc, 177 cc), and in 3D by dividing anal canal into 4 × 2.1 mm grids.

KEY RESULTS

Relaxation pressure progressively increases along anal canal with increasing balloon volume up to 71 cc and thereafter plateaus. In 3D, RAIR is maximally seen at the middle and upper portions of anal canal (levels 1.2-3.2 cm) and posteriorly. Peak residual pressure was seen at proximal anal canal.

CONCLUSIONS & INFERENCES

Recto-anal inhibitory reflex is characterized by differential anal relaxation along anterior-posterior axis, longitudinally along the length of anal canal, and it depends on the rectal distention volume. It is maximally seen at internal anal sphincter pressure zone. Multidimensional analyses indicate that external anal sphincter provides bulk of anal residual pressure. Our findings emphasize importance of sensor location and orientation; as anterior and more distal location may miss RAIR.

The change pattern of SP and NO in the portal vein during the RAIR

PURPOSE

To investigate the change pattern of substance P (SP) and nitric oxide (NO) in the portal vein during the recto-anal inhibitory reflex (RAIR), and its physiological significance; the influence of external splanchnic nerve (ESN) of rectum and anus to the RAIR.

MATERIALS AND METHODS

Seventy-six rats divided into five groups according to the distance of Foley's tube in the rectum and whether or not to cut off ESN supply to the rectum and anal canal, to measure the values of SP and NO in the portal vein during the RAIR.

RESULTS

The stimulus in rectum can cause change of SP and NO in portal vein. The greatest increase of SP is at the 6-cm group. The 6-cm group with total ESN supply had significant difference compared with the 4-cm group before and after the ESN supply and control group were cut (P<0.01). After cutting-off ESN, the increase of SP in the portal vein reduced significantly when compared with the normal ESN supply at the 6-cm group (P<0.05). The greatest change of NO is at the 4-cm group with total ESN. There were significant differences among the 4- and 6-cm groups and control group. After cutting off ESN, the increase of NO was lower than with the intact ESN. There were still differences between the 4- and 6-cm groups and control group(P<0.05).

CONCLUSION

The stimulations at different points of the rectum cause different SP and NO change in the portal vein. This may be the explanation why the stimulation on the different points on the rectum induces different change pattern of RAIR from the neurotransmitters point. The ESN supplies of the rectum and anal canal have an influence on the change of SP and NO in the portal vein during RAIR.

Intestinal sensitivity testing by transmucosal electrical nerve stimulation: stimulus parameters to induce conscious perception

Intestinal sensitivity can be tested using transmucosal electrical nerve stimulation. The aim of this study was to establish the stimulus characteristics that determine perception. In six healthy subjects constant current electrical stimuli were applied via an intrajejunal bipolar electrode while measuring perception. Intensity-response tests with stimuli trains of various frequencies (5 and 100 Hz) and pulse durations (50 and 1000 mus) were performed. All stimuli within the broad range tested induced similar-type abdominal sensations, but the intensity of the stimuli to produce perception differed depending on both pulse duration and frequency. A 20-fold increase in pulse duration decreased the intensity of perceived stimuli by a factor of 0.34 +/- 0.04 (P < 0.05); a similar increase in pulse frequency decreased the intensity by a 0.63 +/- 0.07 factor (P < 0.05). When the frequency and duration concomitantly increased, the stimulus intensity decreased by the product of both factors (0.22 +/- 0.04). Transmucosal electrical nerve stimulation of the intestine induces perception within a broad range of stimuli. However, the intensity of the stimuli required to activate sensory pathways is primarily weighted by the duration rather than by the frequency of the pulses.

Gastrointestinal perception: pathophysiological implications

Physiological gut stimuli during the digestive process are not normally perceived. However, gut stimuli activate a variety of afferent pathways and in some circumstances may induce conscious sensations. Experimental evidence gathered during the past decade suggests that patients with functional gut disorders and unexplained abdominal symptoms may have a sensory dysfunction of the gut, so that physiological stimuli would induce symptoms. Assessment of visceral sensitivity is still poorly developed, but in analogy to somatosensory testing, differential stimulation of visceral afferents may be achieved by a combination of stimulation techniques, which may help to characterize sensory dysfunctions. Visceral afferent input is modulated by a series of mechanisms at different levels of the brain gut axis, and conceivably, a dysfunction of these regulatory mechanisms could cause hyperalgesia. The sensory dysfunction in functional patients seems associated to altered reflex activity, and both mechanisms may interact to produce the symptoms. Evidence of a gut sensory-reflex dysfunction as a common pathophysiological mechanism in different functional gastrointestinal disorders, would suggest that they are different forms of the same process, and that the clinical manifestations depend on the specific pathways affected.

Pelvic floor study in patients with obstructive defecation: influence of biofeedback

The aim of this study was to evaluate the pathophysiologic abnormalities in patients with obstructive defecation or dyssynergia and to assess the role of biofeedback treatment. Three groups were studied. Group A had 24 patients with obstructive defecation; B, 25 patients with constipation; and C, 22 healthy volunteers. Rectosigmoid segmental transit time of group A was 28.5 hours (SD +/- 13.4); B, 17.2 hours (SD +/- 11.5); and C, 8.5 hours (SD +/- 6.3) (p < 0.05). There was no statistical difference in resting and squeezing anal pressure among the three groups. Anorectal angle at rest revealed no difference among the three groups. At strain, a statistically significant difference between groups A and C (p < 0.05) and a marginal difference between groups A and B was noted. Rectocele of the anterior rectal wall was present at strain in 17/24 patients of group A and 7/22 patients of group C (p < 0.05). Electromyography during strain revealed abnormal contractions of puborectalis muscle and external anal sphincter, in 13 and 14 patients of group A, respectively, which differed from that observed in groups B and C (p < 0.001). Biofeedback treatment was applied with good results in 7 of 11 patients of group A. At six months, constipation relapsed in only one of treated patients. Patients suffering from obstructive defecation seem to have slower rectosigmoid transit time than the others. Defecography shows smaller anorectal angle at strain and rectocele of the anterior rectal wall more often. Abnormal pelvic floor contraction at strain is often noted in anal electromyography. Some of these patients seem to respond favorably to biofeedback treatment.

Local thermal stimulation relaxes hypertonic anal sphincter: evidence of somatoanal reflex

PURPOSE

Although it is generally believed that warm perineal baths reduce pain resulting from anal fissure, complicated hemorrhoids, or anal surgery, the exact mechanisms remain unclear. Because hypertonicity of the internal anal sphincter contributes to increasing pain in these conditions, it has been postulated that warm perineal baths could help to relax the anal sphincter, hence reducing pain. It is our purpose to demonstrate response of the anal sphincter to local thermal stimulation via a somatoanal reflex.

METHODS

Continuous anorectal manometry tracings were obtained from 15 healthy volunteers, 22 patients with hemorrhoid, and 20 patients with anal fissure. Local thermal stimulation was achieved by applying a heat pad on the right infragluteal region (local area), and subsequently on the right first interphalangeal region (control area).

RESULTS

Obvious response to local thermal stimulation was shown by 13.3 percent of volunteers, 36.4 percent of patients with hemorrhoid, and 60 percent of patients with fissure. Heat-sensitive patients who responded to local thermal stimulation were divided to two groups, those with ultraslow waves and those without ultraslow waves. In patients with ultraslow waves, the amplitude of ultraslow waves decreased significantly after local thermal stimulation, with amplitude before local thermal stimulation, (mean +/- standard deviation) 66.2 +/- 30.6 mmHg, and during local thermal stimulation, 43.2 +/- 22.3 mmHg, respectively, P = 0.003. By contrast, in patients without ultraslow waves, the tonic pressure measured before local thermal stimulation and during local thermal stimulation was 74.2 +/- 23.5 and 60.5 +/- 18.5 mmHg, respectively, P = 0.001. The response began at approximately three minutes after local thermal stimulation when the skin temperature was 42.1 +/- 0.3 degrees C. No anal response was observed when the heat pad was applied to the control area. The maximum resting pressure of the heat-sensitive patients was significantly higher than that of the nonresponding patients (97.3 +/- 0.1 vs. 76.9 +/- 23.3 mmHg; P = 0.012).

CONCLUSIONS

Local thermal stimulation evokes relaxation of the hypertonic internal anal sphincter through a somatoanal reflex, thus providing an easy and feasible method of clinical application.

The recto-anal inhibitory reflex: abnormal response in diabetics suggests an intrinsic neuroenteropathy

As electrical stimulation of the rectum has been shown to result in reflex internal sphincter inhibition mediated by intrinsic nerves, we aimed to evaluate the integrity of these nerves in the rectum of diabetic patients. Anal canal pressure, recto-anal inhibitory reflex (RAIR) and continence were evaluated in 30 diabetic patients (male:female 13:17, median age 57 years, range 37-70) and these data were compared with similar data obtained from 22 age- and sex-matched healthy controls (male:female 9:13, median age 51 years, range 19-65 years). Median duration of diabetes was 8 years (range 3-30). Twelve (40%) of the 30 diabetics had impaired continence for gas (n = 12) and liquid faeces (n = 3). None of the controls had incontinence. Median maximum resting anal canal pressure (MRP) was: patients 30 mmHg (range 20-75 mmHg) versus controls 40 mmHg (range 20-105 mmHg, P = 0.61). Median maximum squeeze pressure (MSP) was 65 mmHg (range 30-150 mmHg) in patients versus 84mmHg (range 35-230 mm Hg) in controls (P = 0.59). Median threshold rectal mucosal electrosensation (RMES-T) was 27mA (5-40 mA) in patients versus 13 mA (5-28 mA) in controls (P = 0.03). Maximum tolerable rectal mucosal electrosensation was 40 mA (20-60) in patients versus 20 mA (10-30), in controls (P = 0.042, all comparisons using the Wilcoxon rank test). Recto-anal inhibitory reflex was present in eight, abnormal in five (one incontinent) and absent in 17 (11 incontinent) diabetics, while it was present in 18 and abnormal in four controls (test of proportion, P = 0.031). Blood glucose in diabetics on the day of the procedure was 98 mg/dL (70-165 mg/dL). Rectal mucosal electrosensitivity and RAIR were impaired in significantly more patients with diabetes than controls, implying impairment of intrinsic neuronal function. The recto-anal inhibitory reflex was either impaired or absent in all diabetic patients with incontinence.

Internal anal sphincter: advances and insights

The internal anal sphincter, the smooth muscle component of the anal sphincter complex, has an ambiguous role in maintaining anal continence. Despite its significant contribution to resting anal canal pressures, even total division of the internal anal sphincter in surgery for anal fistulas may fail to compromise continence in otherwise healthy subjects. However, recently reported abnormalities of the innervation and reflex response of the internal anal sphincter in patients with fecal incontinence indicate its significance in maintaining continence. The advent of sphincter-saving surgery and restorative proctocolectomy has re-emphasized the major contribution of the internal anal sphincter to resting pressure and its significance in preventing fecal leakage. The variable effect of rectal excision on rectoanal inhibitory reflex has led to a reappraisal of the significance of this reflex in discrimination of rectal contents and its impact on anal continence. Electromyographic, manometric, and ultrasonographic evaluation of the internal anal sphincter has provided new insights into its pathophysiology. This article reviews advances in our understanding of internal anal sphincter physiology in health and disease.

Clinical features of idiopathic megarectum and idiopathic megacolon

BACKGROUND

Dilatation of the rectum and/or colon, in the absence of demonstrable organic disease, is an uncommon and poorly characterised condition.

AIMS

To characterise the clinical and diagnostic features, and response to treatment, of patients with idiopathic megarectum (IMR) and idiopathic megacolon (IMC).

METHODS

A retrospective review was undertaken of all patients operated on for these conditions over a 23 year period. In addition all patients treated over a three year period were prospectively studied by means of a questionnaire, contrast studies of the upper and lower intestine, spine x rays to exclude spinal dysraphism, anorectal physiological studies, and assessment of clinical outcome. Patients with Hirschsprung's disease and other known causes of gut dilatation were excluded.

RESULTS

(i) Retrospective study: Of 63 operated patients, 22 had IMR, 23 had IMR and IMC, and 18 had IMC only. Five patients with IMC had previous sigmoid volvulus, and three had associated non-gastrointestinal congenital abnormalities. Faecal incontinence was always associated with rectal impaction and 14 patients (82%) with IMR alone had had manual disimpaction. (ii) Prospective study: Twenty two patients had IMR, with a median rectal diameter of 10 cm (normal < 6.5 cm). Six patients had IMC and one patient had IMR and IMC. Patients with IMR were significantly (p = 0.0007) younger than patients with IMC. All patients with IMR became symptomatic in childhood, compared with half the patients with IMC who developed symptoms as adults. Patients with IMR all presented with soiling and impaction, compared with patients with IMC whose symptoms were variable and included constipation or increased bowel frequency, pain, and variable need for laxatives. No upper gut dilatation was seen in either group of patients. Spinal dysraphism was seen in two of 18 patients with IMR and two of four with IMC, suggesting extrinsic denervation as a possible cause in a minority. Twelve of 22 patients with IMR had a maximum anal resting pressure below normal, indicating sphincter damage or inhibition. Both IMR and IMC patients had altered rectal sensitivity to distension, suggesting that despite lack of dilatation the rectum in IMC has altered viscoelasticity, tone, or sensory function. Fifteen of 22 patients with IMR were successfully managed with laxatives or enemas, but seven required surgery. Two of seven patients with IMC required surgery, including one for sigmoid volvulus.

CONCLUSIONS

Patients with IMR differ clinically, diagnostically, and in their outcome from patients with IMC. These conditions demand specific investigation, and intensive treatment, to achieve optimum care.

Primary degeneration of the internal anal sphincter as a cause of passive faecal incontinence

BACKGROUND

Faecal incontinence is usually attributed to pelvic-floor denervation of striated muscle or direct sphincter trauma. We have identified a cause of passive faecal incontinence related to degeneration of the internal anal sphincter smooth muscle, in the absence of denervation, structural damage, external-sphincter weakness, or sensory abnormalities.

METHODS

Patients were included on the basis of: passive faecal incontinence, no urge faecal incontinence, low anal pressure whilst at rest, normal anal-squeeze pressure, endosonographically confirmed circumferentially intact internal and external anal sphincters, and normal pudendal nerve terminal nerve latencies. In a second analysis done to assess the proportion of patients with this disorder, we recorded the cause of incontinence in consecutive patients seen during a 6-month period.

FINDINGS

45 patients (35 women, median age 63 years, range 23-80 years) fulfilled the diagnostic criteria. Median duration of symptoms was 2 years (3 months to 20 years). Nine of the 35 women were nulliparous. The median resting anal pressure was 40 cm water (16-56 cm water, normal > 60 cm water). Endosonography revealed an internal sphincter that was thin and hyperechogenic, and had a poorly defined edge. The normal increase in the thickness of the internal anal sphincter with age was not seen. Anal-squeeze pressure, sensitivity, and pudendal nerve latencies were normal. In the second analysis the condition was identified in eight of 230 patients, representing 4% of new referrals.

INTERPRETATION

Primary degeneration of the internal anal sphincter smooth muscle is a discrete clinical condition causing passive faecal incontinence.

Nerves that say NO: a new perspective on the human rectoanal inhibitory reflex

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Physiology of ileal pouch-anal anastomosis. Current concepts

PURPOSE

Increasing experience with ileal pouch-anal anastomosis (IPAA) associated with increasing knowledge about anorectal physiology has lead to a large number of publications. The purpose of this review is to evaluate the current understanding of fecal continence as revealed by the evolution of the ileoanal procedure.

METHODS

Review of the literature covering the most important physiologic parameters involved in fecal continence was undertaken.

RESULTS

Rectoanal inhibitory reflex is probably absent after IPAA but is preserved when distal anorectal mucosa is spared. Anal resting pressure decreases but is less affected when the internal anal sphincter is less traumatized. Squeeze pressure is not importantly affected, and the importance of reservoir function as a determinant of stool frequency is emphasized. IPAA does not affect the coordination between pouch and anal canal motility in the majority of cases. Normal continence is preserved, even during the night, by preserving a gradient of pressure between the pouch and anal canal.

CONCLUSIONS

Physiologic concepts are well established, but controversies about the continence mechanism related to IPAA remain. The IPAA procedure has allowed discrimination of details about the function of multiple structures involved in fecal continence.

Distribution of nitric oxide synthase containing neurons in the rectal myenteric plexus and anal canal. Morphologic evidence that nitric oxide mediates the rectoanal inhibitory reflex

PURPOSE

Following the demonstration that a novel neurotransmitter, nitric oxide (NO), is released during neurogenic relaxation of the internal anal sphincter in vitro, it has been suggested that NO could mediate the rectoanal inhibitory reflex in vivo. The aim of this study was to establish whether the distribution of NO-producing nerves in the anorectum is consistent with this proposed role.

METHODS

NO is synthesized in neurons which contain the enzyme nitric oxide synthase and their presence in the anorectum was determined in tissue obtained from nine abdominoperineal and three anterior resection specimens in patients undergoing surgery for rectal carcinoma. Cryostat sections were stained for nitric oxide synthase immunoreactivity, pan-neuronal/axonal immunoreactivity, and NADPH diaphorase activity.

RESULTS

Nitric oxide synthase immunoreactivity is present in a subpopulation of neurons in rectal myenteric ganglia which also contain NADPH diaphorase activity. Use of the latter histochemical technique enabled the structure and distribution of nitric oxide synthase containing neurons to be determined in whole-mount preparations. Individual neurons have Dogiel type 1 morphology and are present throughout the rectal myenteric plexus. In the distal rectum, positively stained axons enter shunt fascicles which descend into the anal canal, where they ramify into and throughout the internal anal sphincter. Within the sphincter, positively stained nerves lie in close proximity to smooth muscle cells.

CONCLUSION

These results are consistent with the hypothesis that NO is the neurotransmitter that mediates the rectoanal inhibitory reflex.

Anorectal function

A review in a historic perspective of the present knowledge of anorectal physiology is presented. The techniques used in the anorectal physiology laboratory are discussed. Application of new sophisticated techniques to anorectal physiology research in recent years continue to improve our knowledge of anorectal function. Anal continence and defecation depend on both the anal sphincter and the rectum. The assessment of patients with functional anorectal diseases should include a more complete physiologic evaluation of the anorectum than used previously.

Anorectal motor physiology and pathophysiology

Disorders of anorectal function are complex. A clear definition of the underlying pathophysiologic process is possible only with the use of the anal physiology laboratory. A reasonable treatment plan is then possible.

Abnormal visceral autonomic innervation in neurogenic faecal incontinence

Changes of denervation in the anal sphincter striated and smooth muscle in patients with neurogenic faecal incontinence are well established. This study aimed to determine if there is also a more proximal visceral autonomic abnormality. Thirty women with purely neurogenic faecal incontinence (prolonged pudendal nerve latencies and an intact sphincter ring) and 12 patients with neuropathic changes together with an anatomical disruption were studied. Two control groups consisted of 18 healthy volunteer women and 17 women with normal innervation but an anatomically disrupted sphincter. Rectal sensation was assessed using balloon distension and electrical mucosal stimulation, and anal sensation by electrical stimulation. Rectal compliance was studied to determine whether sensory changes were primary or caused by altered rectal wall viscoelastic properties. Anal canal pressure changes in response to both rectal distension and rectal electrical stimulation were measured to assess the intrinsic innervation of the internal anal sphincter. Patients with neurogenic incontinence alone had impaired rectal sensation to distension (53.1 v 31.5 ml, p < 0.05, neurogenic v controls) and to electrical stimulation (24.4 v 14.8 mA, p < 0.005). Patients with neurogenic incontinence and sphincter disruption also showed impaired sensation compared with healthy controls (55.8 ml v 31.5 ml, p < 0.05 and 22.9 mA v 14.8 mA, p < 0.05). Patients with only a disrupted sphincter had normal visceral sensation to both types of testing. Both rectal compliance and the response of the internal anal sphincter to rectal distension and electrical stimulation were normal in all patient groups. This study suggests that there is a visceral sensory abnormality in patients with neurogenic incontinence which is not caused by altered rectal compliance. As evaluated in this study the intrinsic innervation of the internal anal sphincter is not affected in this process.

The internal anal sphincter: mechanisms of control and its role in maintaining anal continence

The human IAS has particular structural and functional characteristics. This smooth muscle constantly generates rhythmic electrical slow waves, but no action potentials. The slow waves are linked to calcium fluxes and both are essential for mechanical activity, i.e. the ASPW. The IAS is pharmacologically characterized by the presence of alpha excitatory and beta inhibitory adrenergic receptors. Cholinergic drugs have an indirect effect through the release of an inhibitory neurotransmitter, very probably VIP, from NANC nerves. The myogenic activity of the IAS is enhanced by its extrinsic sympathetic innervation. Thus, at rest, the IAS is in a state of partial tetanus and contributes approximately 55% of the MABP. Because the IAS ring cannot be completely closed, the anal mucosa and the haemorrhoidal plexuses fill the gap. By compressing these tissues, the IAS perfectly closes the anal canal to retain not only solids but also fluid stool and gas. Acute rectal distension and rectal activity, mainly through intramural pathways, induce reflex IAS relaxation, permitting the rectal contents to be sampled by receptors in the upper anal canal while continence is temporarily maintained by EAS activity and by expansion of the haemorrhoidal cushions. There is a correlation between the volume of rectal distension and the parameters of IAS relaxation. At maximal IAS relaxation, ASPW are absent, indicating the completeness of the inhibition. Although this RAIR is not essential for defecation, insufficient relaxation may be implicated in constipation. Hyperactivity of the IAS resulting in a high MABP and AUSPW has been considered both as a cause and as an effect in haemorrhoids and anal fissure. Continence for fluids and gas is impaired if IAS activity is decreased (i.e. a low MABP), either by direct trauma or by damage of its sympathetic innervation. Severe faecal incontinence will develop when the contractility of both the IAS and the EAS is affected.

Role of surgical treatment in patients with severe constipation

Surgery for severe constipation is necessary in only a small minority of patients. For those patients with a normal diameter colon, the standard procedure remains a colectomy with ileorectal anastomosis. Although the bowel frequency is usually improved, a third of patients experience post-operative diarrhoea, 10% remain constipated, and two thirds continue to experience some pain. Psychological evaluation is essential preoperatively. In patients with an idiopathic megarectum or megacolon, the best operation is less well defined. In those patients with a moderately dilated rectum or colon, a colonic resection offers the best results with a low morbidity. In those patients with a widely dilated rectum, a Duhamel procedure is reasonable but there is a higher morbidity and the results are less uniformly satisfactory.