7 Questions About Anorectal Manometry and Pelvic Floor Studies in Constipation

1. Why do I need to know about defecatory disorders? 

Defecation requires increased rectal pressure coordinated with relaxation of the anal sphincter and pelvic floor. Some patients with chronic constipation have defecatory disorders (DDs). In contrast to normal or isolated slow transit constipation, these should be treated with pelvic floor biofeedback therapy rather than laxatives.1,2

2. What is the utility of clinical features for diagnosing DD?

In studies, some symptoms (e.g., a sense of anorectal blockage or anal digitation) suggest, but are not sufficient to diagnose, a DD. I find that more nuanced symptoms — such as the difficulty evacuating not only hard but also soft stools or enemas, prolonged defecation (e.g., 15 minutes or longer), or the need to assume different positions to defecate — are more useful for identifying DD. Also, remember, many patients with DDs have upper gastrointestinal symptoms, such as nausea, regurgitation and abdominal bloating. A meticulous digital rectal examination — with assessment of anal sphincter and puborectalis tone at rest — when patients contract the muscles and then strain as if to defecate is also helpful. In one study, the positive predictive value for digital rectal examination was 61 percent, and the negative predictive value was 91 percent. Therefore, anorectal tests are necessary to diagnose DD in constipated patients who do not respond to simple laxatives.

3. Which of the three diagnostic tests (anorectal manometry,rectal balloon expulsion test, or barium or MR defecography) is most helpful for diagnosing DD?

The rectal balloon expulsion test (BET) is the most useful diagnostic test for diagnosing DD, and it requires no specialized equipment (table 1). When the clinical index of suspicion for DD is high, an abnormal rectal BET is sufficient to diagnose the condition, and a normal BET might be a false negative result. Further testing is generally necessary. When the clinical index of suspicion is low and the rectal BET is normal, no further tests are necessary. When the BET is abnormal, anorectal manometry and/or defecography are required to clarify the diagnosis. Manometry alone is of limited utility for diagnosing DD. Anorectal manometry and a rectal BET are generally performed during the same visit. It is unacceptable to do an anorectal manometry without a rectal BET.

Table 1:Common Anorectal Tests Used in Clinical Practice

Anorectal Parameter
 Methodological Issues Clinical Utility
Internal and external
sphincter function and
rectoanal coordination
(Rectoanal pressure gradient)
  • Manometry utilizes traditional (water-perfused or solid-state) or newer (highresolution
  • and high-definition) techniques.
  • Methods for anal manometry and definitions of parameters (e.g., maximum
  • squeeze pressure) are poorly standardized.
  • Normal values, especially resting pressure, are technique dependent, lower in
  • women than men, and decline with age.
  • Age-adjusted and gender-adjusted normal values are not universally used to interpret patient data in clinical practice.
  • Rectoanal gradient during evacuation is usedfor identifying DD. However, its utility is limited by overlap between asymptomatic subjects and patients with DD. Some patients with DD haveanal hypertension (high resting pressure).
Rectal evacuation (Rectal
balloon expulsion test)
  • Generally, rectal balloon expulsion time is measured with a balloon inflated to 50 ml of water. Normally, a subject takes less than minute to expel a balloon; a patient with a DD requires longer. In women 50 years or older, the upper limit for normal balloon expulsion is 15 seconds.
  • Abnormal rectal balloon expulsion is a useful, highly sensitive and specific first-line test for diagnosing DD in clinical practice.
Anorectal and pelvic floor
motion and rectal evacuation
(Proctography with
fluoroscopy or MRI)
  • After adding barium paste (defecography) or ultrasound gel (MRI) to the rectum, images are acquired during pelvic floor contraction and rectal evacuation. Barium is added to the bladder, small intestine and vagina to visualize these organs by defecography.
  • Advantages of MRI include lack of radiation, ability to perform multiplanar imaging, and better visualization of bony landmarks, pelvic floor and other organs; hence, measurements are more reproducible. However, an MRI is generally performed in the supine position.
  • Useful when anorectal manometry and rectal balloon expulsion are equivocal in patients with suspected DD; also useful in patients with pelvic organ prolapse.
  • Patients with DD might have impaired rectal evacuation, pelvic organ prolapse (rectoceles), and normal, reduced or increased perineal descent.

4. What are the options for conducting anorectal manometry? 

Water-perfused or solid-state catheters work well but have been replaced with high-resolution manometry (HRM) and high-definition manometry (HDM) catheters that measure circumferential pressures throughout the anal canal and the lower rectum withouthaving to be moved.3 Hence, it takes less time to do a manometry with HRM or HDM than with catheters that are not high resolution.Some patients find the HDM catheter, which is larger (10.75 mm diameter), uncomfortable. There is no evidence that HRM or HDM is better for diagnosing anorectal disorders than non-high-resolution systems. Manometry catheters that rely on air-filled sensors, which might be portable, less expensive and capable of being used for office-based manometry, are also available.

5. What are the manometry criteria for diagnosing DD?

The traditional criteria were an inadequate increase in rectal pressure (e.g., less than 40 mm Hg), which reflected a poor propulsive force, impaired anal relaxation (equal to or less than 20 percent baseline pressure), or both.4 However, a considerable proportion of asymptomatic healthy people, approximately 20 percent with non-HRM and 80 percent with HRM, have features of DD. This limits the diagnostic utility of HRM for diagnosing DD. Besides impaired rectal evacuation, HRM might uncover features suggestive of rectal prolapse or large rectocele.5

6. What is the role of barium and MRI defecography for diagnosing DD?

Compared to a BET, barium defecography is more involved and entails radiation exposure. In the U.S., defecography is performed when a structural cause of DD is suspected, when the results of manometry and a rectal BET are equivocal, or in patients who have a normal manometry with an abnormal BET. In the latter category, it is likely that the prolonged BET reflects impaired evacuation; some of these patients have structural causes for impaired evacuation. Remember, most structural abnormalities (e.g., rectal intussusception) in DD probably reflect excessive straining and/or are a consequence rather than a cause of DD. The latter category includes large enteroceles that compress the rectum and preclude evacuation or large rectoceles that trap stool. MR defecography has some advantages over barium defecography. It is particularly useful with clinically suspected structural lesions (e.g., large rectoceles, uterine prolapse or cystocele), particularly when surgery is being considered, and it is useful for diagnosing DD in patients with clinically suspected DD and normal BETs. Indeed, in one study, over 90 percent of patients with typical symptoms and rectoceles or enteroceles had normal rectal BETs.5

7. What else is important?

Even asymptomatic people might have “abnormal” tests. Perhaps this is because they find it awkward to simulate defecation in the left lateral position. Test results must be interpreted in the context of clinical features and age-adjusted and sex-adjusted normal values, which are not widely available. Adequate training and experience are essential to interpret manometry studies. Because artifact is common, tracings must be reviewed to ensure the software-generated reports are accurate. Pressure drift, which is partly due to differences between room and body temperature, affects the accuracy of pressure measurements with certain HRM systems. This pressure drift is only partly corrected by the analysis software program.


Anorectal tests are very useful for diagnosing DD, particularly when these tests are conducted and interpreted by experienced personnel, in the clinical context and with an understanding of the strengths and limitations of these tests.

Dr. Bharucha has received royalties from Medspira and consulting fees from Allergan, Plc.

1.Bharucha, A.E., Pemberton, J.H., Locke, G.R. AGA Practice Guideline on Constipation: Technical Review. Gastroenterology. 2013;144(1):218–38.
2.Bharucha, A.E., Dorn, S. D., Lembo, A., Pressman,A. American Gastroenterological Association Medical Position Statement on Constipation. Gastroenterology.2013;144(1):211–17.
3.Lee, T.H., Bharucha, A.E. How to Perform and Interpret a High-Resolution Anorectal Manometry Test. Neurogastroenterol Motil. 2016;22(1):46–59.
4.Grossi, U., Carrington, E. V., Bharucha, A.E., Horrocks, E.J., Scott, S. M., Knowles, C. H. Diagnostic Accuracy Study of Anorectal Manometry for Diagnosis of Dyssynergic Defecation. Gut. 2016;65(3):447–55.
5.Prichard, D.O., Lee, T., Parthasarathy, G., Fletcher, J.G., Zinsmeister, A.R., Bharucha, A.E.H.High-Resolution Rectoanal Manometry for Identifying Defecatory Disorders and Rectal Structural Abnormalities in Women. Clin Gastroenterol Hepatol. 2017;15(3):412–420.5.

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