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Anorectal Function & Defecography

Anorectal manometry (ARM), endoanal ultrasound (EAUS), and defecography answer complementary functional and anatomic questions. No single test is a gold standard; interpret the findings with symptoms and the testing protocol.[1][2]

Rome V (2026) lists dyssynergic defecation separately and requires difficult-evacuation symptoms in at least 25% of bowel movements for the past three months, with onset at least six months earlier, plus abnormal balloon expulsion, a reduced rectoanal gradient or abnormal evacuation pattern on manometry, or impaired evacuation on defecography.[21] One abnormal test supports probable dyssynergic defecation; two abnormal test categories support definite dyssynergic defecation.[21] It replaces the Rome IV framework that required abnormalities in two categories. Rome V also recognizes rectal hypo- and hypersensitivity as anorectal sensory dysfunction disorders.[23]

Anorectal Manometry (ARM)​

ARM is the primary functional assessment of anorectal sensorimotor physiology. It measures resting and squeeze pressures, rectal sensation, the rectoanal inhibitory reflex (RAIR), and rectoanal coordination during simulated evacuation. Rectal compliance can be estimated during ARM, but a barostat measures it more accurately.[3][1]

Technique and Parameters​

High-resolution manometry (HRM) catheters with closely spaced sensors now provide superior spatial resolution without requiring a pull-through maneuver. Measurements include:

  • Resting anal pressure. Resting pressure predominantly reflects internal anal sphincter tone; continence also depends on stool consistency, rectal function, sensation, and other pelvic-floor muscles.
  • Squeeze pressure increment. The increment reflects external anal sphincter and puborectalis function.
  • Rectoanal gradient during evacuation (rectal pressure minus anal pressure). In a study of 474 constipated patients (420 women), a reduced gradient was 36% sensitive and 85% specific for prolonged balloon expulsion.[4]
  • RAIR. Its absence can raise suspicion for Hirschsprung disease; technical factors and other causes of an absent reflex require consideration.
  • Rectal sensation thresholds. Balloon distension records first sensation, desire, urgency, and maximum tolerated sensation. In patients meeting symptom and exclusion criteria, Rome V rectal hyposensitivity requires at least two thresholds more than 2 SD above the upper normal limit; hypersensitivity requires at least one desire, urgency, maximum-tolerated, or pain threshold more than 2 SD below the lower normal limit, excluding first sensation.[21]

Pressures must be compared with age- and sex-matched reference values using the same catheter system, as values differ between conventional and HRM devices. Apparent dyssynergic patterns also occur in healthy volunteers, particularly during nonphysiologic simulated evacuation; correlate with symptoms, BET, and the testing protocol.[1]

Indications in Urogynecology​

  • Defecatory dysfunction or obstructed defecation. ARM and balloon expulsion test (BET) is the recommended initial evaluation when conservative management (fiber, laxatives) fails. In the Blackett cohort, these combinations corresponded to reduced evacuation probabilities of 14% with both tests normal, 45% with either abnormal, and 75% with both abnormal; 158 of the 474 participants underwent defecography.[4][2]
  • Fecal incontinence. ARM identifies low resting pressure (IAS dysfunction), low squeeze pressure (EAS dysfunction), impaired sensation, and reduced compliance. The ACG recommends ARM in patients who fail conservative measures, particularly to guide biofeedback therapy.[1] ASCRS 2023 says anorectal physiology testing can be considered to define dysfunction and guide management , but it notes that the testing does not routinely change management and cannot reliably identify who will respond to sacral neuromodulation or colostomy.[6] Pudendal nerve terminal motor latency testing is not routinely recommended .[6]
  • Preoperative assessment. Assess for functional evacuation disorders when obstructed-defecation symptoms accompany a structural abnormality; choose ARM or BET when the result could change treatment or surgical planning.[5]
  • Guiding biofeedback. ARM can guide coordination training. ASCRS recommends biofeedback as first-line treatment for symptomatic pelvic-floor dyssynergia, alongside management of contributing constipation.[2][6]

Limitations​

ARM does not reliably predict which patients will benefit from sacral neuromodulation or colostomy.[6] False-positive and false-negative results are common, and seated manometry may be more discriminating than left-lateral positioning, though confirmatory data are still emerging.[1]

Pudendal nerve terminal motor latency (PNTML) is a separate neurophysiologic test, historically used to infer pudendal neuropathy, that does not correlate well with anal sphincter pressure and does not reliably guide fecal-incontinence therapy. A 2018 retrospective review found no useful contribution to treatment decisions, and the American Gastroenterological Association's 1999 position statement already advised against using PNTML to evaluate fecal incontinence. PNTML is not part of the recommended evaluation sequence above.[19]

Endoanal Ultrasound (EAUS)​

EAUS is the reference standard for imaging anal-sphincter anatomy and identifying structural defects of the internal and external anal sphincters.[7][6]

Technique​

A rotating endoanal transducer (typically 7–15 MHz) is inserted into the anal canal, providing 360° cross-sectional images. 3D EAUS provides volumetric data and improved characterization of defect extent. Distinct layers visualized:[7][8]

  • Anal mucosa (innermost)
  • Internal anal sphincter (IAS): hypoechoic ring
  • Longitudinal muscle and intersphincteric space
  • External anal sphincter (EAS): hyperechoic ring
  • Puborectalis / pubococcygeus (upper anal canal)

IAS tears appear as hyperechoic defects within the hypoechoic muscle, while EAS tears appear as hypoechoic defects within the hyperechoic muscle.[7]

Indications in Urogynecology​

  • Obstetric anal sphincter injuries (OASIS). EAUS defines residual sphincter anatomy in specialist OASI assessment. Historical occult-injury rates after vaginal delivery vary with population, technique, timing and defect definition.[7][17] In the prospective study that first described occult injury, Sultan and colleagues (1993) found a sphincter defect on endosonography 6 weeks after vaginal delivery in 28 of 79 primiparous women (35%), persisting in all 22 restudied at 6 months; defects followed 8 of 10 forceps deliveries, no cesarean delivery produced a new defect, and defects were strongly associated with bowel symptoms (p < 0.001).[20] The 2015 RCOG guideline reports sonographic sphincter abnormalities in 33% of women after vaginal delivery, but endoanal ultrasound performed immediately after delivery did not significantly increase detection over clinical examination; it advised regarding immediate postpartum ultrasound as a research tool because of availability, image quality, interpretation skill and acceptability.[18]
  • Fecal incontinence evaluation. ASCRS 2023 says EAUS may be useful to evaluate sphincter anatomy when a repair is planned , particularly after vaginal delivery; a sphincter defect on imaging does not by itself predict symptomatic incontinence, and defect size does not necessarily track severity.[6] Complete characterization requires description of both IAS and EAS injury extent, perineal-body size, and defect length relative to total sphincter length.[6][7]
  • Preoperative surgical planning. EAUS defines sphincter anatomy when sphincteroplasty is being considered.[6] Sacral neuromodulation remains an option with or without a defect.[6]
  • Postpartum assessment. The 2026 IUGA guideline supports EAUS and, where available, ARM at least six weeks postpartum in women with OASI to inform specialist follow-up and subsequent-birth counseling. If EAUS is unavailable, transperineal ultrasound may screen for residual defects; suspected defects should receive EAUS confirmation.[17]

EAUS vs. Alternative Ultrasound Modalities​

A multisociety consensus (ASCRS, AUGS, IUGA, ICS, SAR, SGS) established that endoanal pelvic-floor ultrasound is the criterion standard (94% consensus) for sphincter-integrity assessment.[7] Exoanal alternatives are increasingly studied:

  • Transperineal ultrasound (TPUS). In 59 women assessed six months after OASI repair, TPUS and EAUS defect scores correlated strongly (ρ 0.74–0.77), but correlations with symptoms were weak.[11] A separate cross-sectional study of 196 previously vaginally parous women (29 reporting anal incontinence) found strong associations between significant defects and symptoms (OR 46 for TPUS; 38 for EAUS).[10]
  • 3D introital or transperineal ultrasound. High negative predictive values (0.85–0.93) make them suitable for screening for an intact sphincter, but low positive predictive values (0.37–0.63) mean that identified defects should be confirmed with EAUS.[12]
  • MRI. Superior to EAUS for distinguishing EAS tear from scar and for identifying external-sphincter atrophy, but EAUS better visualizes the IAS.[1]

What the randomized evidence establishes​

The 2015 Cochrane review found one RCT of 752 primiparous women with clinically diagnosed second-degree tears, testing EAUS before repair, not routine scanning after repair. Severe anal incontinence at 12 months was less frequent (RR 0.48, 95% CI 0.24–0.97; 684 assessed), but three-month perineal pain increased (RR 5.86, 95% CI 1.74–19.72). There was no clear improvement in overall anal incontinence or quality of life.[9]

Limitations​

EAUS is operator-dependent and requires specialized training. Even asymptomatic women can have postpartum sphincter defects, and findings require clinical correlation. EAUS does not assess dynamic pelvic-floor function (prolapse, intussusception) unless advanced dynamic techniques are used, which are not widely available.[6]

Defecography​

Defecography directly images the process of rectal evacuation and evaluates both structural and functional causes of defecatory dysfunction.[2] It is available in two forms: fluoroscopic (barium) and MRI defecography.

Fluoroscopic Defecography​

Barium paste is instilled into the rectum and lateral fluoroscopic images are acquired at rest, during squeeze, straining, and evacuation while the patient sits on a commode. Opacification of the vagina and oral contrast for small bowel allows multicompartment assessment.[13][14]

Pathology detected:

  • Rectocele (size and contrast retention)
  • Rectal intussusception (intrarectal, intra-anal, or external)
  • Enterocele or sigmoidocele. Can coexist with or mimic a rectocele; imaging can clarify the contents of a clinically uncertain posterior bulge.[13]
  • Rectal prolapse
  • Perineal descent. Interpret with symptoms and the imaging protocol.
  • Dyssynergic defecation. Failed or prolonged evacuation, paradoxical narrowing of anorectal angle.

A review cited by ASCRS included 7,519 barium and 668 MR examinations from selected constipated cohorts; in barium-defecography analyses, high-grade intussusception occurred in 23.7%, rectoceles >4 cm in 15.9%, enterocele in 16.8%, and perineal descent in 44.4%.[2]

Advantages. Fluoroscopic defecography is performed in the physiologic seated position, which has the greatest construct validity for evacuation, and directly visualizes evacuation dynamics. It detects clinically occult structural pathology that alters surgical planning in some patients.[13][14][2]

Limitations. Radiation exposure varies by equipment and protocol; limited soft-tissue contrast; operator-dependent; limited reproducibility of anorectal-angle measurements (improved with standardized techniques).[1][14]

MRI Defecography​

MRI defecography uses rectal gel contrast and acquires dynamic sequences during rest, contraction, straining, and evacuation. In women, when imaging is indicated because examination is incomplete or discordant with symptoms, or complex evacuation or surgical anatomy needs clarification, ACR considers MR defecography an appropriate option.[13][5]

Quantitative parameters:[15][5]

  • Pubococcygeal line (PCL). Reference line from inferior pubic symphysis to last coccygeal joint; organ descent measured relative to this line.
  • H-line (anteroposterior width of levator hiatus) and M-line (descent of levator hiatus below PCL).
  • Anorectal angle. Usually narrows with squeeze and opens during evacuation.[5] Absolute measurements depend on technique.[5]
  • Levator-plate angle. Describes the orientation of the levator plate and is read together with the H-line and M-line.

Strengths and interpretation:

  • No radiation exposure.
  • Detailed multicompartment and soft-tissue assessment. Simultaneously evaluates anterior (cystocele, urethral hypermobility), middle (uterovaginal prolapse), and posterior (rectocele, enterocele, intussusception) compartments.[15][13]
  • MRI assesses levator ani muscle defects with high interobserver reliability on static T2-weighted images.[13]
  • Post-defecation straining identified additional or maximal anterior and middle descent in a retrospective 65-patient study.[16]

Limitations. Performed in the supine position (may underestimate rectal intussusception and rectocele compared with seated fluoroscopy); lower agreement with surgical findings for full-thickness rectal prolapse and peritoneocele compared with fluoroscopic defecography; less widely available and more expensive.[1][13]

Integrated Diagnostic Approach​

ModalityPrimary AssessmentStrengthsLimitations
Anorectal ManometryFunctional: sphincter pressures, rectal sensation, rectoanal coordinationIdentifies dyssynergia, guides biofeedback, quantifies sphincter weaknessAbnormal simulated-evacuation patterns can occur in healthy people; position and protocol dependent
Endoanal UltrasoundStructural: anal-sphincter anatomy and defectsReference standard for IAS / EAS defect identification; informs sphincteroplasty planningOperator-dependent; defect presence does not predict symptom severity; does not assess dynamic function
Fluoroscopic DefecographyStructural and functional: evacuation dynamics, prolapseSeated position (physiologic); detects occult enteroceles, intussusception, sigmoidocelesRadiation exposure; limited soft-tissue contrast
MRI DefecographyStructural and functional: multicompartment prolapse, levator anatomyNo radiation; comprehensive 3-compartment assessment; levator-muscle evaluationSupine position may underestimate posterior pathology; less available; more expensive

A commonly used evaluation pathway, drawn from ACG, ASCRS and ACR guidance, is:[1][13][2]

  1. Suspected evacuation disorder: perform a digital rectal examination, then use ARM and BET when obstructed-defecation symptoms persist despite conservative treatment.[1][2]
  2. Defecography (fluoroscopic or MRI) when there is discordance between ARM / BET and clinical findings, when multicompartment prolapse is suspected, or when surgical planning requires anatomic detail. For women with obstructed defecation and posterior-compartment prolapse, the 2026 IUGA opinion calls a seated defecating proctogram the standard investigation to assess rectal intussusception and enterocele.[22]
  3. EAUS when fecal incontinence is present with suspected sphincter injury, particularly if sphincteroplasty is being considered.

Treat relevant functional evacuation disorders before attributing symptoms to an incidental rectocele or other structural finding.[2][5]

ASCRS 2024 describes the BET (time to expel a 50 mL water-filled balloon) as reproducible and highly specific, with a sensitivity of about 50%, and able to predict response to biofeedback. It recommends evaluating for outlet dysfunction with anorectal physiology testing or dynamic imaging (fluoroscopic or MR defecography, dynamic ultrasound) in patients who fail diet, fiber and osmotic laxatives .[2]

See Also​

References​

1. Wald A, Bharucha AE, Limketkai B, et al. "ACG Clinical Guidelines: Management of Benign Anorectal Disorders." Am J Gastroenterol. 2021;116(10):1987-2008. doi:10.14309/ajg.0000000000001507

2. Alavi K, Thorsen AJ, Fang SH, et al. "The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Evaluation and Management of Chronic Constipation." Dis Colon Rectum. 2024;67(10):1244-1257. doi:10.1097/DCR.0000000000003430

3. Bharucha AE, Basilisco G, Malcolm A, et al. "Review of the Indications, Methods, and Clinical Utility of Anorectal Manometry and the Rectal Balloon Expulsion Test." Neurogastroenterol Motil. 2022;34(9):e14335. doi:10.1111/nmo.14335

4. Blackett JW, Gautam M, Mishra R, et al. "Comparison of Anorectal Manometry, Rectal Balloon Expulsion Test, and Defecography for Diagnosing Defecatory Disorders." Gastroenterology. 2022;163(6):1582-1592.e2. doi:10.1053/j.gastro.2022.08.034

5. Gurland BH, Khatri G, Ram R, et al. "Consensus Definitions and Interpretation Templates for Magnetic Resonance Imaging of Defecatory Pelvic Floor Disorders: Pelvic Floor Disorders Consortium." AJR Am J Roentgenol. 2021;217(4):800-812. doi:10.2214/AJR.21.26488

6. Bordeianou LG, Thorsen AJ, Keller DS, et al. "The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Fecal Incontinence." Dis Colon Rectum. 2023;66(5):647-661. doi:10.1097/DCR.0000000000002776

7. Alshiek J, Murad-Regadas SM, Mellgren A, et al. "Consensus Definitions and Interpretation Templates for Dynamic Ultrasound Imaging of Defecatory Pelvic Floor Disorders: Pelvic Floor Disorders Consortium." Dis Colon Rectum. 2023;66(2):200-216. doi:10.1097/DCR.0000000000002651

8. Rao SS. "Diagnosis and Management of Fecal Incontinence." Am J Gastroenterol. 2004;99(8):1585-1604. doi:10.1111/j.1572-0241.2004.40105.x

9. Walsh KA, Grivell RM. "Use of Endoanal Ultrasound for Reducing the Risk of Complications Related to Anal Sphincter Injury After Vaginal Birth." Cochrane Database Syst Rev. 2015;(10):CD010826. doi:10.1002/14651858.CD010826.pub2

10. Zhao B, Li Y, Tang Y, et al. "Assessing Obstetric Anal Sphincter Injuries: A Comparison of Exoanal and Endoanal Ultrasound." J Ultrasound Med. 2023;42(9):2031-2038. doi:10.1002/jum.16221

11. Stuart A, Ignell C, Örnö AK. "Comparison of Transperineal and Endoanal Ultrasound in Detecting Residual Obstetric Anal Sphincter Injury." Acta Obstet Gynecol Scand. 2019;98(12):1624-1631. doi:10.1111/aogs.13701

12. Taithongchai A, van Gruting IMA, Volløyhaug I, et al. "Comparing the Diagnostic Accuracy of 3 Ultrasound Modalities for Diagnosing Obstetric Anal Sphincter Injuries." Am J Obstet Gynecol. 2019;221(2):134.e1-134.e9. doi:10.1016/j.ajog.2019.04.009

13. Khatri G, Bhosale PR, Robbins JB, et al. "ACR Appropriateness Criteria® Pelvic Floor Dysfunction in Females." J Am Coll Radiol. 2022;19(5S):S137-S155. doi:10.1016/j.jacr.2022.02.016

14. Paquette I, Rosman D, El Sayed R, et al. "Consensus Definitions and Interpretation Templates for Fluoroscopic Imaging of Defecatory Pelvic Floor Disorders: Pelvic Floor Disorders Consortium." Dis Colon Rectum. 2021;64(1):31-44. doi:10.1097/DCR.0000000000001829

15. Pugliesi RA, Cannella R, Vernuccio F, et al. "Pelvic Floor Dysfunction: Anatomical Characterization and Functional Imaging With MRI Defecography." Eur J Radiol. 2026;196:112706. doi:10.1016/j.ejrad.2026.112706

16. Ye P, Ning G, Cui T, et al. "Magnetic Resonance Defecography: Post-Defecation Straining Detects More and Maximal Prolapse in the Anterior and Middle Compartments." Eur J Radiol. 2024;181:111757. doi:10.1016/j.ejrad.2024.111757

17. Sultan AH, Okeahialam NA, De Leeuw J, et al. IUGA International Guidelines on Obstetric Anal Sphincter Injuries. Int Urogynecol J. 2026;37:2223–2280. doi:10.1007/s00192-026-06642-3.

18. Royal College of Obstetricians and Gynaecologists. The Management of Third- and Fourth-Degree Perineal Tears. Green-top Guideline No. 29. London: RCOG; June 2015.

19. Saraidaridis JT, Molina G, Savit LR, et al. Pudendal Nerve Terminal Motor Latency Testing Does Not Provide Useful Information in Guiding Therapy for Fecal Incontinence. Int J Colorectal Dis. 2018;33(3):305-310. doi:10.1007/s00384-017-2959-5

20. Sultan AH, Kamm MA, Hudson CN, Thomas JM, Bartram CI. "Anal-Sphincter Disruption During Vaginal Delivery." N Engl J Med. 1993;329(26):1905-1911. doi:10.1056/NEJM199312233292601

21. Rao SSC, Bharucha AE, Carrington EV, et al. "Anorectal Disorders." Gastroenterology. 2026;170(6):1318-1346. doi:10.1053/j.gastro.2026.01.037

22. Rachaneni S, Dietz HP, Latthe P, Sirany A, Spivak A, Dua A. "IUGA Opinion Paper on Obstructed Defecation: Management of Clinical and Proctographic Rectoceles." Int Urogynecol J. 2026;37(1):75-85. doi:10.1007/s00192-025-06288-7

23. Drossman DA, Chang L, Tack J. "Disorders of Gut–Brain Interaction and the Rome V Process." Gastroenterology. 2026;170(6):1083–1098. doi:10.1053/j.gastro.2026.02.014.