AGA technical review on anorectal testing techniques

Diamant, N.E.; Kamm, M.A.; Wald, A.; Whitehead, W.E.

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Volume 116, Issue 3 , Pages 735-760, March 1999

AGA technical review on anorectal testing techniques☆

This Technical Review has been endorsed in principle by the American Association for the Study of Liver Disease, the American College of Gastroenterology, and the American Society for Gastrointestinal Endoscopy

Article Outline

Abstract
The literature
Definitions
Anatomic and physiological considerations
Techniques
Tests for specific diagnosis or management
- Fecal incontinence
Constipation/impaired defecation
Proctalgia and other sensory syndromes
Acknowledgements
References
Copyright

Abstract

This literature review and the recommendations therein were prepared for the American Gastroenterological Association Clinical Practice and Practice Economics Committee. Following external review, the paper was approved by the committee on May 17, 1998.

GASTROENTEROLOGY 1999;116:735-760

Anorectal symptoms and disorders are some of the most common and distressing experienced in all ages of the population. Fecal incontinence is reported in 3%–8% of the population.¹, ², ³ Symptoms compatible with constipation are found in 3%–20% of the population; the prevalence increases to 20%–25% in the elderly.¹, ³, ⁴, ⁵ Anorectal pain compatible with the levator ani syndrome and proctalgia fugax occur in 5%–8% of the population.³, ⁶ Therefore, a multitude of tests have arisen over the years for assessment of the sensory-motor aspects of the anorectal region. This review evaluates the pertinent literature and the information at hand to provide some direction for the use of the various techniques in patients with these conditions. An attempt has been made to identify the capability of different tests to assess aspects of the defecation and continence mechanisms and the sensory mechanisms involved with symptom production. The review does not describe the technical details of each test (“how to”) or the clinical diagnostic and therapeutic paradigms for their use in different disorders (“when to”). The information is primarily derived from and directed to the adult population, although some mention is made of the pediatric age group as well.

Anorectal symptoms often are not isolated phenomena but can be associated with more generalized systemic or organic diseases (e.g., diabetes with neuropathy, collagen vascular disorders, neural or muscular diseases), and with functional disorders, particularly the irritable bowel syndrome.¹, ², ³, ⁴, ⁵, ⁷

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The literature

Upon review of the literature on the value of anorectal tests, few large-scale studies are found (1) that have attempted to validate anorectal tests against other techniques, and (2) that include properly controlled treatment trials with placebo components, adequate control populations, and careful outcome assessment. Therefore, most attention has been directed to studies that use sample sizes larger than 25, use objective physiological assessments for comparison, and, in treatment trials, include adequate assessments before and after treatment. The articles were gleaned from a MEDLINE search for the 10 years preceding June 1996 and from the bibliography of recent reviews.

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Definitions

The symptom complexes related to the anorectal area, particularly definition of terms such as fecal incontinence and constipation, allow for considerable debate. Terms such as dyschezia and tenesmus, although defined by consensus,⁸ are better ignored because of the many meanings attached to them and the overlap in meaning between the two terms and other definitions of constipation and irritable bowel syndrome. Therefore, in this review, broad definitions are used without limitation as to the presence of organic disease or structural abnormality on one hand or a functional basis for the symptoms on the other. A functional disorder has been defined as “a variable combination of chronic or recurrent gastrointestinal symptoms not explained by biochemical or chemical abnormalities.”⁹ However, when specific disease entities, structural abnormalities, or functional syndromes have an impact on the use of the techniques, these conditions are incorporated into the discussion.

Fecal incontinence

The first part of the definition proposed by the Rome criteria on the basis of symptoms⁹, ¹⁰ can provide a broad basis for inclusion in the category of fecal incontinence: continuous or recurrent uncontrolled passage of fecal material (>10 mL) for at least 1 month in an individual older than 3 years of age. The American Psychiatric Association sets the age at older than 4 years.¹¹

Constipation

Constipation may be conventionally defined by three parameters: symptoms, measurements of defecation, and physiological measurements.⁸ Based on symptoms alone, functional constipation according to the Rome criteria¹⁰ can be defined as the presence of two or more of the following symptoms for at least 3 months: (1) straining at defecation at least one fourth of the time, (2) lumpy and/or hard stools at least one fourth of the time, (3) sensation of incomplete evacuation at least one fourth of the time, and (4) two or fewer bowel movements per week. In this review, constipation is considered to fall under two broad categories: slow colonic transit and anorectal dysfunction leading to impaired evacuation. This review does not deal with tests for the slow transit type of constipation, but concentrates on testing that identifies the role played by the anorectal area. Therefore, terms such as outlet obstruction, anismus, pelvic floor dyssynergia, and paradoxical contraction of pelvic musculature are included under the definition of constipation.

Levator ani syndrome

The levator ani syndrome (puborectalis syndrome, chronic proctalgia, pyriformis syndrome, and pelvic tension myalgia) has been defined by consensus in the Rome criteria⁹ as (1) chronic or recurrent anorectal pain or aching for at least 3 months, (2) episodes that last 20 minutes or longer, and (3) exclusion of other likely organic causes of rectal pain.

Proctalgia fugax

This syndrome is defined by the Rome criteria⁹ as (1) recurrent episodes of midline pain localized to the anus or lower rectum for at least 3 months, (2) episodes lasting from seconds to minutes, (3) absence of anorectal pain between episodes, and (4) lack of evidence for anorectal disease.

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Anatomic and physiological considerations

The mechanisms and structures involved in the process of defecation and in the maintenance of continence are multiple and complex (Figure 1).

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Fig. 1.
Anatomy of the anal canal, rectum, and distal colon illustrating the mechanisms for preserving continence. (Reprinted with permission.¹⁷)

Overall control involves both voluntary and involuntary components. Colonic and anorectal function are integrated and interrelated. The anal sphincter has both smooth muscle and striated muscle components. Other striated muscles of the pelvic floor, including the puborectalis and levator muscles, perform important functions. Both sensory and motor innervation occur through several nerves including the lumbar colonic nerves, the pudendal nerves, and pelvic nerves with connections to the spinal cord levels from at least L2 to S4. Simple reflexes such as relaxation of the anal sphincter with distention of the rectum, as well as more complicated function such as reservoir function of the rectum, can vary considerably in health and disease. Psychobehavioral factors have an impact on function of the anorectum to the full defecation process. Therefore, it is unreasonable to expect that any single test, or even a battery of tests, can fully characterize each anorectal sensory and motor disorder responsible for the different symptoms and syndromes in this area, whether these be of structural or organic disease origin or functional in nature. However, using a constellation of investigations it is often possible to characterize precisely the nature of a disorder, leading to specific therapies with well-documented outcomes. More detailed descriptions of the anatomy and innervation and of the mechanisms of defecation and continence can be found in recent articles.¹², ¹³

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Techniques

History

A complete detailed history is essential to direction of diagnostic and therapeutic approaches to the patient with anorectal symptoms and disorders. Diaries and questionnaires are useful adjuncts in this regard.

Diaries

Symptom diaries are useful for three purposes: (1) diagnostic evaluation, (2) monitoring of compliance with treatment, and (3) measurement of efficacy of treatment. The diary is a simple, inexpensive way to obtain “objective,” prospective information on stool frequency and consistency, on the nature and frequency of incontinence, and on the occurrence of other symptoms such as pain. Diaries cannot predict colonic transit, rectal emptying, or the cause of impaired defecation.¹⁴ Although not completely specific or sensitive for slow transit, they do give some guides; patients with documented infrequent bowel movements are likely to have slow transit.¹⁵, ¹⁶ Symptom diaries should be considered and described to the patient as aids to memory. Therefore, they must be simple and short. Symptom diaries are discussed at greater length, and a sample is provided, in an earlier review.¹⁷

In disorders such as fecal incontinence, it is important to identify the circumstances in which symptoms occur as a means of identifying the most effective strategies for treatment.¹⁸, ¹⁹ For example, documentation that fecal incontinence is less likely the day after a large bowel movement and more likely when several days have passed without a sizable bowel movement is helpful in suggesting the diagnosis of overflow incontinence.

Symptom diaries are often used in clinical trials to measure outcome²⁰, ²¹ and are similarly useful in treating individual patients. Symptom diaries are believed to be more objective than patient recall at a scheduled office visit because recall is strongly influenced by poor memory of events and by the relative prominence of the most recent and most severe events.²² A daily record of whether instructions were followed will help to identify problems with treatment adherence that can be addressed with the patient, as well as indicating when a treatment is not working.

Conclusion

Symptom diaries are recommended for (1) diagnostic evaluation, (2) monitoring of adherence to treatment recommendations, and (3) measurement of efficacy of treatment in patients with constipation and fecal incontinence.

Questionnaires

Symptom questionnaires, filled out by the patient before the first evaluation, can significantly speed up the interview by identifying areas that can be skipped and by giving the patient a chance to look up and record information on medications and prior illnesses. More importantly, questionnaires help clinicians avoid overlooking significant symptoms that may not be part of the reason the patient is in the clinic but should nevertheless be identified and evaluated in the context of the presenting complaint.

A variety of gastrointestinal symptom questionnaires are available, although most are oriented toward the detection of functional disorders such as the irritable bowel syndrome.²³, ²⁴, ²⁵ The most thoroughly validated and extensively used questionnaire is the Mayo Clinic Bowel Symptom Questionnaire developed by Talley et al.²⁶ The Mayo questionnaire has been adapted for use in an elderly population.²⁷ Thompson and Heaton⁴ developed a structured interview for lower bowel symptoms. The questionnaire developed by Drossman,²⁸ based on the Rome multinational working team reports, is used to identify patients with any of a number of functional gastrointestinal disorders. Drossman et al.²⁹ subsequently developed a short Functional Bowel Disease Severity Index for grading the severity of symptoms in patients with chronic abdominal pain, the irritable bowel syndrome, or other functional bowel disorders. However, this index does not address anorectal disorders.

Conclusion

At present, there is no symptom questionnaire that satisfactorily addresses anorectal disorders.

Physical examination

A complete physical examination will identify certain structural disorders (e.g., prolapse, perineal disease) and local and systemic disease processes that may affect anorectal function and dysfunction. In addition, some assessment of perineal innervation can be obtained through observation of perianal sensation and reflex contraction of the external anal sphincter to perianal stimulation and to a cough.

There is limited information on the relationship between specific physical examination maneuvers and objective tests of anorectal function. However, some studies address the agreement between anal canal pressure measurements and digital examination. In a study of 66 patients, Hallan et al.³⁰ found that digital examination by an experienced surgeon correlated (r = 0.56; P < 0.001) with anal canal resting pressure, and digital examination correlated (r = 0.72; P < 0.001) with maximum squeeze pressure, although in individual patients the digital assessment was often inaccurate. Similar observations were made by Felt-Bersma et al.³¹ in a study of 280 patients. In a study of 64 patients, Eckardt and Kanzler³² found agreement between digital examination results and resting anal canal pressure of 0.41 (contingency coefficient) and the agreement between digital examination results and squeeze pressure of 0.52. These correlations with objective measurements are too low to support the use of digital examination alone in the diagnostic assessment of sphincter function. Hallan et al.³⁰ found the agreement between independent digital examination results to be comparable to the agreement between results of different manometric examinations. This finding suggests that day-to-day variations in anal canal pressures account for some of the differences between independent digital examination results. Physical examination may also provide some qualitative assessment of the levator ani and puborectalis muscle contractions and tenderness. Digital examination will identify fecal impaction in most patients but will miss 30% of fecal impactions in the elderly because a large amount of feces in the upper rectum and in sigmoid colon seen on radiographs may not extend into the distal rectum in reach of the examining finger.³³

Measurement of pelvic floor descent can be done objectively. Henry et al.³⁴ developed a mechanical device that can be used externally to quantitatively locate the perineal surface of the anal canal relative to the ischial tuberosities. With the patient in the left lateral position, measurements are made at rest and with straining. However, simple observation of the level of the perineum relative to the ischial tuberosities is adequate. The perineum should not descend beyond the outlet of the bony pelvis on straining effort.

Conclusion

In experienced hands, assessment of the anal sphincter by digital examination provides limited qualitative assessment of sphincter resting and squeeze pressures.

Endoscopy

Rigid or flexible examination of the large bowel is an essential part of the examination of every new patient with anorectal symptoms. They may provide information about disease such as a benign or malignant obstructing lesion and mucosal inflammation. Although not as precise as lateral radiography, these examinations may suggest the presence of a megarectum or megacolon.

Conclusion

Endoscopy is necessary to exclude organic disease in patients with fecal incontinence, constipation, or proctalgia.

Imaging techniques

Barium enema

Barium enema is useful primarily for colonic assessment. In patients with a history or examination results suggestive of megarectum or megacolon, there is interest in the rectal and sigmoid dimensions. In these patients, some investigators believe that the optimal investigation is a water-soluble contrast study without bowel preparation.³⁵ Of particular interest are the precise rectal dimensions and the proximal extent of large bowel dilation. Megarectum can be defined as a transverse diameter of the rectum at the pelvic brim larger than 6.5 cm.³⁶ Barium radiographs will show the characteristic denervated bowel segment with proximal dilatation of the colon in Hirschsprung's disease,³⁷ but they do not reliably distinguish between so-called short-segment Hirschsprung's disease and idiopathic constipation.³⁸

Conclusion

Barium enema is not usually necessary for assessment of the anorectal area in patients with fecal incontinence or constipation, except to help exclude intraluminal mucosal disease or to assess bowel dilation.

Evacuation proctography (defecography)

Evacuation proctography (defecography) involves imaging the rectum with contrast material and observation of the process, rate, and completeness of rectal evacuation using fluoroscopic techniques.³⁹, ⁴⁰, ⁴¹, ⁴², ⁴³, ⁴⁴ A variety of contrast materials have been used, including esophageal contrast barium and barium mixed with oatmeal or other viscous materials. It is not a study of normal defecation, is not performed in response to a desire to defecate, and lacks the normal electromuscular events associated with defecation. Some patients' embarrassment at the nature and the setting of the test may inhibit normal emptying of the contrast material.

Defecography has been criticized on a number of grounds. First, there is poor agreement between independent observers in the measurement of the anorectal angle, a parameter thought to be critical to the interpretation of defecography results.⁴⁵, ⁴⁶ It is uncertain whether the central axis of the rectum,⁴¹, ⁴⁴ the entire posterior wall of the rectum,⁴⁷ or the most distal portion of the posterior wall³⁹, ⁴⁰, ⁴³, ⁴⁴, ⁴⁸ should be used. Second, some of the findings often reported on this examination, especially rectocele, descent of the pelvic floor, and internal intussusception, are seen in a large proportion of asymptomatic individuals,⁴³, ⁴⁴, ⁴⁸, ⁴⁹ and the presence of these entities does not correlate with impaired rectal emptying.⁴⁹ Third, normal values of rectal emptying vary widely.⁵⁰, ⁵¹ Fourth, rectal evacuation does not correlate with symptoms (infrequent defecation vs. impaired defecation), colonic transit, or anal manometry results.⁴⁹, ⁵⁰ Finally, several investigators have argued that defecography adds little data to the results of anorectal manometry⁵², ⁵³ and/or does not differentiate patients with impaired defecation from those with fecal incontinence or normal controls.⁵⁴ However, there are some potential uses of this technique.

There is some merit to the objective demonstration of a large rectocele in patients who complain of incomplete evacuation, particularly those who are helped by rectal or vaginal digitation during defecation. However, rectoceles smaller than 2 cm in diameter are normal in women.⁴⁴ Even large rectoceles are not always associated with symptoms, and correlation between the presence of such a finding, symptoms, and improvement with surgical treatment is not always good.⁵⁵

Internal rectal intussusception has been implicated as a cause of symptoms and of solitary rectal ulcer. However, its correction correlates poorly with symptomatic benefit, and mucosal prolapse and rectal intussusception have been reported in normal subjects.⁴⁴, ⁵⁶

Defecography can be used to determine external rectal prolapse.⁵⁷, ⁵⁸, ⁵⁹, ⁶⁰, ⁶¹, ⁶² However, it should be possible to demonstrate external prolapse on the commode without radiology.

Defecography combined with filling of the small bowel with barium from above may be useful in demonstrating an enterocele,⁴¹ and as such may be a useful adjunctive test in the evaluation of patients with impaired defecation and proctalgia.

In theory, quantification of rectal evacuation could be helpful in patients with constipation, especially those with pelvic floor dysfunction or dyssynergia.³⁹, ⁴⁰, ⁴¹, ⁴², ⁶³ For example, some patients with constipation have poor rectal emptying on proctography.⁴⁹, ⁶⁴ However, in one recent study, no differences were observed in patterns of rectal emptying of barium contrast among four study groups: patients with infrequent defecation and normal colonic transit, patients with infrequent defecation with proximal slowing of colonic transit, patients with defecatory difficulty only, and control subjects.⁴⁹ Furthermore, in younger patients with constipation, information about evacuation has not been proven to alter treatment or to predict the outcome of treatments such as colectomy.⁶⁵ Therefore, although defecography may disclose significant differences between constipated patients and controls, the degree of overlap renders these studies of limited importance in management decisions. However, if the results of defecography (e.g., inappropriate contraction of the puborectalis muscle) corroborate the results of other studies of anorectal function, they may serve to reinforce the validity of such testing (see discussions of neuromuscular function, anorectal monitoring, constipation, and tests for specific diagnosis or management [constipation/impaired defecation, biofeedback] in this review).

An alternative to proctography involves quantitative measurement of the rate and completeness of rectal evacuation.⁶⁶ One hundred milliliters of barium paste is inserted into the rectum, and the patient is asked to evacuate as rapidly and completely as possible. The maximum emptying rate, time to achieve maximum emptying, and proportion of barium evacuated are measured using a weight transducer. Normal subjects evacuate quickly and completely. Patients with severe constipation demonstrate a variable evacuation disturbance. Results obtained using this technique have been shown to correlate well with the percentage change in area on evacuation proctography.⁶⁷ Similar semiquantitative observations about rectal emptying can be made by using a paste containing a radioisotope that can be placed into the rectum and the amount evacuated accurately quantified.⁴⁷, ⁵⁰, ⁶⁸ A low-radiation isotope such as ^99mTc exposes the patient to a lower radiation dose than proctography. Two studies have found that rectal emptying of 200 mL of an isotope-labeled artificial stool varies widely among normal controls, ranging from 28% to 98% in 26 control subjects.⁵⁰, ⁵¹ Either total evacuation volumes of 18 constipated subjects were similar to those of controls (mean, 64%; range, 34%–91%), although mean evacuation rates (percent per second) were significantly slower in the constipated patients,⁵¹ or evacuation was less in constipated patients than in controls; however, there was a wide overlap between the two groups.⁵⁰, ⁶⁹ Measurement of rectal emptying by these two techniques does not give anatomic information about rectal and anal configuration and the changes during emptying.

Another technique, balloon proctography, was introduced before defecography with the intention of outlining the rectum during rectal evacuation.⁷⁰ A balloon filled with radiolabeled water (scintigraphic balloon topography) has also been used to measure the anorectal angle.⁷¹ These techniques depend on the balloon contour's conforming to the rectum. Balloon proctography has been superceded by evacuation proctography, with direct contrast instillation into the rectum.

Conclusion

(1) Evacuation proctography is not of established value in patients with fecal incontinence. (2) Proctography is of potential value in patients with constipation in whom the following problems are suspected as the cause of impaired defecation: inappropriate contraction of the puborectalis muscle, enterocele (e.g., after hysterectomy), and anterior rectocele (e.g., history of manipulation of the rectal wall per vagina). Otherwise, there is no support for the routine use of this technique.

Anal ultrasonography

The ability to image the sphincter muscles accurately using anal endosonography has radically altered understanding of the pathogenesis of fecal incontinence as well as its investigation and management.⁷², ⁷³ Abnormalities of structural integrity involving either muscle can be clearly identified. The procedure is rapid and without radiation exposure, but interpretation is very dependent on the operator. However, anal canal ultrasonography has a high degree of sensitivity and specificity, approaching 100% in the hands of experienced investigators, in identification of anatomic defects in both the external and internal anal sphincters as well as more subtle abnormalities of internal sphincter smooth muscle texture and composition.⁷⁴, ⁷⁵, ⁷⁶, ⁷⁷, ⁷⁸ In vitro and in vivo dissection studies have shown close correlation between the endosonographic image and anatomic structures.⁷⁹, ⁸⁰

The endosonographic probe rotates through 360° inside a hard plastic cone of 15-mm diameter and provides an image of the internal and external anal sphincters. A plastic cone over the rotating endoprobe provides a superior image to that obtained with a probe covered by a water-filled balloon, as is used in rectal endosonography. Two main probe frequencies have been used. Both 7-MHz and 10-MHz probes provide good resolution of the anal sphincter muscles, but the resolution is slightly superior with the latter. The internal sphincter is seen as a dark homogeneous ring (Figure 2).

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Fig. 2.
Normal anal ultrasound scan showing the anal sphincter muscles in cross section through the mid anal canal. The darker homogenous ring is the IAS smooth muscle (I). The white heterogeneous ring surrounding this is the EAS (arrows; E). The top of the figure is anterior.

Anal endosonography also allows delineation of the external anal sphincter, although the interpretation of these images is much more subjective than interpretation of those of the internal anal sphincter. There is more anatomic variation of the external sphincter, especially anteriorly. This is clinically important if obstetric damage is not to be overdiagnosed. In women, vaginal as well as anal placement of the probe may be used.⁸¹

Using endosonography and manometry, it is at times possible to link different symptoms of incontinence with different muscle pathologies. Passive fecal incontinence, the loss of stool without the patient's awareness, is related to dysfunction of the internal anal sphincter, whereas urge incontinence, the loss of stool because of an inability to suppress defecation, is related to external anal sphincter dysfunction.⁸²

Anal endosonography has been used in assessment of internal anal sphincter defects, such as those that occur after anal stretching,⁸³ anal sexual abuse,⁸⁴ and lateral sphincterotomy.⁸⁵ Degeneration of the internal sphincter, as in progressive systemic sclerosis, is also visible.⁸⁶ Although the internal sphincter is not surgically repairable on its own, the delineation of pathology does allow increased understanding of the disease process and suggests treatment with either a supportive medical approach or newer surgical techniques designed to increase resting tone.

Ultrasonography has been compared to mapping of the external anal sphincter with needle electromyography and has been found to be slightly more accurate⁷⁷ and better tolerated.⁷⁴, ⁸⁷ Ultrasonography is also more accurate than anorectal manometry,⁷⁷ including vectormanometry. Therefore, anal endosonography has decreased the need for some other investigations, such as electromyography, to identify external anal sphincter defects⁷⁵ and to provide the potential for more definitive therapy, such as surgical correction of the defect. Use of anal endosonography in patients with obstetrical injury is a prime example (Figure 3).

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Fig. 3.
Anal ultrasound scan of a woman with anterior obstetric sphincter damage. The top of the figure is anterior. There is disruption of both the IAS (small arrows) and EAS (large arrows) muscles.

In one study, 35% of primiparae who delivered vaginally developed a sphincter defect involving one or both muscles.⁸⁸ Only 4% of multipara developed new defects. These women can present soon after delivery or up to many years later. Symptoms can date back to the delivery or develop later in life. In women with fecal incontinence in whom the only apparent risk factor is obstetric damage, 90% have endosonographic evidence of structural abnormality of one or both sphincter muscles.⁸⁹, ⁹⁰, ⁹¹ In a recent series, 55 consecutive women with obstetric-related incontinence for solid or liquid stool had external sphincter damage accurately characterized using endosonography and physiological tests and were treated by anterior overlap sphincter repair.⁹² Eighty percent of patients became either fully continent or incontinent for gas only; only 2 patients remained incontinent for solid stool. Symptomatic improvement correlated closely with the ability to endosonographically identify overlapping muscle postoperatively. Another study of 28 patients with obstetric injury reported similar results.⁹³

Anal endosonography has also been useful in women who have had third-degree tears and experienced continued symptoms, despite a primary sphincter repair. There is a high incidence of persisting structural damage in these women.⁹⁴, ⁹⁵ In one study of 34 women who sustained third-degree tears, half of the women with repaired third-degree tears still had symptoms of anal incontinence or urgency. Sonographic sphincter defects were identified in 85% of those with third-degree tears compared with 33% of control subjects who had not sustained tears.⁹⁵

Therefore, accurate delineation of structural damage using endosonography allows for correct selection of patients for surgical repair and for postoperative assessment of patients. The relationship between the nature, location, and extent of the structural damage and symptoms requires further testing.

Conclusion

Anal ultrasonography is presently the simplest, most reliable, least invasive test for definition of anatomic defects in the external and internal anal sphincters.

Magnetic resonance imaging and computed tomographic scanning

Computed tomographic scanning has little place in the evaluation of anal disease because of its poor resolution of this small area and because of the radiation exposure. However, magnetic resonance imaging (MRI) may have a role. Although anorectal structures can be visualized using standard MRI techniques, the use of an endoanal coil significantly enhances the resolution and allows precise identification of sphincter muscle structural abnormalities.⁹⁶ Further studies of the value of MRI are needed.

Conclusion

At present, MRI and computed axial tomographic scanning have no defined role in the evaluation of constipation and fecal incontinence.

Colon transit studies

Transit studies are discussed only in the context of anorectal disorders. Transit studies enable a distinction between patients with slow and normal colonic transit times. Despite differences in diet and other factors that might affect colonic transit, studies of normal subjects on diets containing 20–30 g fiber/day indicate a consistent upper range of normal.¹⁴, ⁹⁷, ⁹⁸, ⁹⁹ Although transit times differ between men and women, these differences appear to be inconsequential for clinical purposes.¹⁰⁰ In addition, there are no important differences between the two phases of the menstrual cycle,¹⁰⁰ and colonic transit is similar in young and elderly populations.¹⁰¹

The main benefit of transit studies lies in the ability to objectively confirm patients' subjective complaints of constipation and/or decreased bowel frequency. Patients who complain predominantly of infrequent defecation but who repeatedly have normal colonic transit may consciously or unconsciously misrepresent or misperceive bowel habits.¹⁴, ¹⁰² Therefore, the finding of normal colonic transit on two consecutive studies provides some reassurance that colonic function is appropriate and ends the diagnostic evaluation of patients who complain of infrequent defecation.¹⁰³

In addition to confirmation of slow transit, transit studies can be used for identification of the colonic region(s) in which slow transit occurs. Markers and radioisotopes have been used for this purpose.⁹⁷, ⁹⁸, ⁹⁹, ¹⁰⁴, ¹⁰⁵, ¹⁰⁶, ¹⁰⁷, ¹⁰⁸, ¹⁰⁹, ¹¹⁰ The region of delay defined by radiopaque markers is close to the regions defined using radioisotope.¹⁰⁵

The value of studies documenting regional delays in transit is controversial. In patients in whom study results indicate pelvic floor dysfunction, rectosigmoid transit often is significantly delayed¹¹¹; however, delayed transit through the rectosigmoid or left colon cannot determine pathophysiology, that is, the cause of the delayed transit. Additional studies of anorectal function may help distinguish pelvic floor dysfunction from other causes of delay in the distal colon such as willful deferral of defecation¹¹² and help select patients for biofeedback treatment (see discussions of tests for specific diagnosis or management).

Conclusion

Colon transit studies are useful for (1) objective confirmation of patients' subjective complaint of constipation and/or decreased bowel frequency, (2) confirmation of slow transit, and (3) documentation of regional delays in transit.

Neuromuscular function

Anorectal manometry

The anal canal is defined as the region in which resting pressures are at least 5 mm Hg higher than rectal pressure. Although age does not relate significantly to length, men have longer anal canals than women,¹¹³, ¹¹⁴, ¹¹⁵, ¹¹⁶, ¹¹⁷ albeit with considerable overlap (Table 1).

Table 1. Normal values of length of anal canal

Women (cm)	n	Men (cm)	n	Study
4.0 ± 1.0^a	18	4.0 ± 1.0^a	18	Loening-Baucke and Anuras¹¹³
3.1 (2.0–4.2)^b	20	3.6 (2.4–4.4)^b	20	Rasmussen¹¹⁴
2.2 (2.2–3.8)^a	35	2.8 (2.1–3.7)^a	23^c	Pedersen and Christiansen¹¹⁵
3.7 ± 0.2	10	4.0 ± 0.6^b	12	McHugh and Diamant¹¹⁷
^aNot significantly different. ^bSignificantly different. ^cExpressed as median (range).

NOTE. Values expressed as mean ± SEM or mean (range).

In the proximal anal canal, anterior quadrant pressures are lower than those in the other three quadrants at rest and with maximal squeeze; distally, posterior quadrant pressures are reduced.¹¹⁶ In the mid anal canal, radial pressures are generally equal in all quadrants.

Satisfactory measurements of anal canal pressures and anal sphincter responses can be obtained with open-tipped or side-opening water-perfused catheters, direct online solid-state microtransducers, or air- or water-filled balloons of various sizes and configurations. Large balloon probes are sufficient for assessment of sphincter responses to rectal distention and other stimuli, but they are not able to measure resting pressures of the anal canal. Knowledge of normal values for each technique is required, especially for age and sex differences. Normal anal canal pressures vary according to sex, age, and techniques used (Tables 2 and 3). In general, pressures are higher in men and younger persons, but there is a considerable overlap in values. Studies to date have not included large numbers of subjects in each age group.

Table 2. Representative normal values of maximal resting anal canal pressures determined manometrically

	Women	n	Men	n	Study
Station pull-through	58 ± 3	22	66 ± 6	15	Read et al.¹¹⁹
	54 ± 5	12	Not studied		Caruana et al.¹²⁰
	50 ± 13	18^a	63 ± 12	18	Loening-Baucke and Anuras¹²¹
	49 ± 3	12	49 ± 3	7	Orkin et al.¹²²
Slow pull-through	46 (range, 40–58)	35	60 (range, 51–98)	23	Pedersen and Christiansen¹¹⁵
Rapid pull-through	100 ± 22	10^a	Not studied		Loening-Baucke and Anuras¹¹³
	106 ± 18	10^a	Not studied		Loening-Baucke and Anuras¹¹³
	102 ± 19	35^b	100 ± 21	27^b	McHugh and Diamant¹²³
	76 ± 24	40^c	97 ± 20	31^c	McHugh and Diamant¹²³
	53 ± 22	17^d	72 ± 23	3^d	McHugh and Diamant¹²³
^aSignificant difference between sexes but not between age groups. ^bAges 20–39 years. ^cAges 40–69 years. ^dAges ≥70 years.

NOTE. Values expressed as mm Hg (mean ± SEM) unless indicated.

Table 3. Representative normal values of maximal squeeze anal canal pressures determined manometrically

	Women	n	Men	n	Study
Station pull-through	135 ± 15	22	218 ± 18	15	Read et al.¹¹⁹
	90 ± 9	12	Not studied		Caruana et al.¹²⁰
	159 ± 45	18^a	238 ± 38	18	Loening-Baucke and Anuras¹¹³
Slow pull-through	103 (range, 78–190)	35	163 (range, 76–234)	23	Pedersen and Christiansen¹¹⁵
Rapid pull-through	179 ± 55	10^a	Not studied		Loening-Baucke and Anuras¹¹³
	159 ± 35	10	Not studied		Loening-Baucke and Anuras¹¹³
	171 ± 40	35^b	240 ± 65	27^b	McHugh and Diamant¹²³
	132 ± 169	40^c	203 ± 45	30^c	McHugh and Diamant¹²³
	116 ± 40	17^d	219 ± 32	3^d	McHugh and Diamant¹²³
^aSignificant difference between sexes but not between age groups. ^bAges 20–39 years. ^cAges 40–69 years. ^dAges ≥70 years.

NOTE. Values expressed as mm Hg (mean ± SEM) unless otherwise indicated.

Rogers et al.¹¹⁸ examined the reproducibility of anorectal manometry in 16 patients by having these patients evaluated blindly by two different investigators approximately 20 days apart. The average difference between studies was 10 cm H₂O (95% confidence interval [CI], −25 to 4.7 cm H₂O) for resting pressure, and 9 cm H₂O (CI, −32 to 14 cm H₂O) for squeeze pressure. These confidence intervals are relatively large, amounting to 30% of the range for resting pressure and 22% of the range for squeeze pressure. However, the number of subjects studied was small. In a separate study of 14 subjects, Hallan et al.³⁰ found that independent resting pressure measurements correlated (r = 0.77; P < 0.001), as did independent squeeze pressure measurements (r = 0.66; P < 0.01). Another study in 11 subjects showed that individual variation of resting pressures measured on 2 separate days were less than 12%.¹¹⁷

Resting anal canal pressures

Resting anal canal pressures may be assessed by station pull-through or rapid pull-through techniques.¹¹³, ¹¹⁵, ¹¹⁷, ¹¹⁹, ¹²⁰, ¹²¹, ¹²², ¹²³ Measured pressures tend to be higher with rapid pull-through than with station pull-through techniques (Table 2). Resting pressures reflect the tonic activities of both the internal anal sphincter (IAS) and external anal sphincter (EAS); approximately 75%–85% of this pressure is derived from the IAS. However, if the patient is not completely relaxed, a larger contribution from the EAS (and therefore higher pressures) will be recorded. Resting pressures of the anal canal may be expressed as the average obtained from each transducer or as a range to identify asymmetry of anal canal pressures.¹¹⁶

Squeeze pressures

Squeeze pressures may be obtained by asking the patient to maximally contract the EAS as the probe is sequentially positioned through the anal canal (station pull-through technique) or to squeeze maximally during the rapid pull-through method (Table 3).¹¹³, ¹¹⁵, ¹¹⁷, ¹¹⁹, ¹²⁰, ¹²¹, ¹²³ With the latter method, at least three separate trials are recommended, and maximal pressures from each transducer are averaged. The duration of maximal squeeze should also be obtained (Table 4); methods have varied from a single squeeze to an average of three trials to the minimum pressures that must be sustained during a prolonged squeeze.¹¹⁹, ¹²⁴

Table 4. Duration of EAS maximum squeeze

Duration (s)^a	n	Criteria	Study
49 ± 1	16	Mean 3 trials	Chiarioni¹²⁴
		10 mm Hg ↑ in lower anal canal
122 ± 21	37	5 mm Hg ↑ in lower anal canal	Read et al.¹¹⁹
^aMean ± SEM.

Reflex anal sphincter responses

Normally, the IAS is tonically inhibited either in response to rectal distention or during attempted defecation (Figure 4).

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Fig. 4.
Reflex relaxation of the anal sphincter. The rectal balloon is first rapidly inflated and deflated with 50 mL of air (arrow) using a syringe attached to a three-way stopcock. Reflex relaxation of the IAS is recorded as well as the ability of the patient to sense rectal distention. (Reprinted with permission from Gastroenterology 1974:67;216–220.)

Reflex inhibition may be elicited by distending a rectal balloon with different volumes of air or by asking the subject to expel the manometer (pseudodefecation)¹¹³, ¹²⁰, ¹²⁴, ¹²⁵, ¹²⁶ (Table 5).

Table 5. Thresholds of IAS relaxation

Thresholds (mL)	n	Characteristics of distending balloon	Study
14 ± 1	16	5 cm long, 5 cm from anal verge	Chiarioni¹²⁴
20 (10–30)	11	5 cm long, 5 cm from anal verge	Wald and Tunuguntla¹²⁵
22 ± 3 (10–40)	12	5 cm long, 5 cm from anal verge	Caruara et al.¹²⁰
25 ± 2	17^b	5 cm long, 5 cm from anal verge	Merkel et al.¹²⁶
19 ± 6	18^c	2.5 × 3 cm, 5 cm from anal verge	Loening-Baucke and Anuras¹¹³
23 ± 11	18^d	2.5 × 3 cm, 5 cm from anal verge	Loening-Baucke and Anuras¹¹³
^aMean ± SEM and/or (range). ^bElderly, >age 60 years. ^cElderly, >age 66 years. ^dYoung, ages 21–40 years.

Inhibition of IAS tone is influenced by volume and speed of distention and by rectal volume and compliance; that is, if the rectum is enlarged (megarectum), greater volumes of rectal distention are required to elicit the inhibitory reflex. This balloon distention reflex remains intact in patients with extrinsic denervation but disappears with neuropathy and loss of ganglion cells of the myenteric plexus and/or with atrophy and fibrosis of the IAS.⁸⁶, ¹²⁷ Determination of the clinical importance of distinguishing between neural and muscle abnormality will require further studies. Although EAS inhibition can be satisfactorily assessed with all types of anorectal manometers, simultaneous electromyography (EMG) recordings ensure that decreased pressures are caused by inhibition of EAS activity.

Prolonged anorectal manometry

Methods have been reported to monitor anorectal motor events over prolonged periods and even in fully ambulant subjects. These methods have used pressure microtransducers with or without simultaneous EMG recordings of the EAS¹²⁸, ¹²⁹, ¹³⁰ or a multilumen-perfused sleeve device to monitor anal canal pressures.¹²² These techniques show promise as investigational techniques, but their clinical applicability has not been established.

Vector manometry (vectometry)

This approach assesses the radial pressure profile along the anal sphincter, and it is likely that up to eight radially oriented recording ports are necessary for adequate resolution.¹³¹, ¹³², ¹³³, ¹³⁴ The reproducibility of vectormetric studies has not been reported. However, several studies have reported agreement with ultrasound and needle EMG. Tjandra et al.¹³¹ studied 26 patients with obstructed defecation and 20 patients with fecal incontinence by means of anorectal manometry, vectometry, and anal canal ultrasonography. Based on history and physical examination, 4 of 20 incontinent patients had disruption of the EAS and IAS. This was confirmed by ultrasound examination in all 4 and by vectometrogram in 3 of 4 patients. The false-positive rate was not reported. Similar findings have been reported recently in abstract form.¹³⁵

Braun et al.¹³² studied 23 fecal incontinent female patients, including 11 with sphincter muscle disruption defined by ultrasonography or MRI and 12 with idiopathic fecal incontinence. Those with traumatic sphincter injury showed significantly higher asymmetry indices than patients with idiopathic fecal incontinence or (historical) controls. However, individual values were not given.

Yang and Wexner¹³³ studied 50 consecutive patients with fecal incontinence; 34 (68%) showed abnormal indices of asymmetry. Of 46 patients evaluated by needle EMG, 38 showed evidence of sphincter injury, but in only 5 of the 38 was the defect localized in the same quadrant by vectometry. Of 33 patients tested by ultrasonography, 27 were found to have sphincter defects, but in only 3 was the defect localized to the same quadrant by vectometry. The investigators concluded that vectometry had no apparent value, but they used only four recording ports rather than eight ports at 45° intervals as in some other studies.¹³¹, ¹³², ¹³⁴

Only one study provides data that allow for the calculation of the sensitivity and specificity of vectometry. Perry et al.¹³⁴ studied 69 consecutive women with functional anorectal disorders, including 9 with fecal incontinence dating back to a recognized sphincter injury, 40 with fecal incontinence who were not suspected on clinical grounds of having sphincter injuries, and 20 with chronic constipation who were not suspected of having sphincter injuries. Women in the last two groups were subdivided into those who had or had not had at least one episiotomy each. All subjects in the sphincter injury group had a symmetry index of less than 0.6, resulting in a sensitivity of 100%. When 21 healthy controls, 7 constipated women without episiotomy, and 12 incontinent women without episiotomy were compared, the specificity was 90%. Among incontinent women with a history of episiotomy who were not suspected on clinical grounds of having sphincter injuries, 57% were found to have an abnormal symmetry index of less than 0.6. The authors interpret these data as indicating that vectometry is of clinical value in identification of patients with traumatic sphincter injury. However, the sensitivity and specificity of vector manometry are too low to determine which patients should be treated surgically.

Although some of these data can be interpreted as indicating that vectometry is of clinical value in identification of patients with traumatic sphincter injuries, anal canal ultrasonography is the preferred test for identification of such patients.