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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) now lists dyssynergic defecation separately and requires difficult-evacuation symptoms plus at least one abnormal test category among balloon expulsion, manometry, and evacuation imaging. 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. An incidental abnormal manometric pattern without appropriate symptoms does not establish a clinical disorder.[18]

Anorectal Manometry (ARM)​

ARM is the primary functional assessment of anorectal sensorimotor physiology. It measures resting and squeeze pressures, rectal sensation, rectoanal inhibitory reflex (RAIR), rectal compliance, and rectoanal coordination during simulated evacuation.[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. Key measurements include:

  • Resting anal pressure — predominantly reflects internal anal sphincter tone; continence also depends on stool consistency, rectal function, sensation, and other pelvic-floor muscles.
  • Squeeze pressure 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. This is a study-specific association, not a stand-alone diagnostic threshold.[4]
  • RAIR — its absence can raise suspicion for Hirschsprung disease, but technical factors and other causes of an absent reflex require consideration; manometry alone does not confirm that diagnosis.
  • Rectal sensation thresholds — first sensation, desire to defecate, maximum tolerable volume; identifies hyposensitivity or hypersensitivity.[2]

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 / obstructed defecation. ARM + 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]
  • Preoperative assessment. Assess for functional evacuation disorders when obstructed-defecation symptoms accompany a structural abnormality; choose ARM/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, and its clinical utility for fecal incontinence management beyond biofeedback guidance remains debated.[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]

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 vary with population, technique, timing, and defect definition; they are not a universal prevalence estimate after vaginal delivery.[7][17]
  • Fecal incontinence evaluation. The ASCRS recommends EAUS when a sphincter defect is suspected, particularly with a history of vaginal delivery or when sphincteroplasty is being considered. 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 findings directly influence the decision to proceed with sphincter repair. The presence of a sphincter defect alone does not predict symptomatic fecal incontinence — defect size does not necessarily correlate with symptom severity.[6]
  • Postpartum assessment. The 2026 IUGA guideline supports EAUS and, where available, ARM 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. 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). These are selected-cohort associations, not prospective prediction or proof of interchangeable accuracy.[10][11]
  • 3D introital / 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. This limited trial does not establish universal postpartum ultrasound screening.[9]

Limitations​

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

Defecography​

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

Fluoroscopic Defecography (Cystocolpoproctography)​

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 / 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.[2]
  • Dyssynergic defecation — failed or prolonged evacuation, paradoxical narrowing of anorectal angle.

A review cited by ASCRS pooled 7,519 barium and 668 MR examinations from selected constipated cohorts: high-grade intussusception 23.7%, rectoceles >4 cm 15.9%, enterocele 16.8%, and perineal descent 44.4%. These referral-series frequencies are not population prevalence or indications for repair.[2]

Advantages. Performed in the physiologic seated position (greatest construct validity for evacuation); directly visualizes evacuation dynamics; detects clinically occult structural pathology that alters surgical planning in a significant percentage of 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. When imaging is indicated because examination is incomplete or discordant with symptoms, or complex evacuation/surgical anatomy needs clarification, ACR considers MR defecography an appropriate option. This does not mean routine imaging of every clinically evident prolapse.[13][5]

Key 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. Absolute measurements depend on technique; apparent paradoxical narrowing requires correlation with symptoms and physiology rather than diagnosis from one angle.[5]
  • Levator-plate angle — assesses levator ani integrity.

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]
  • A normal BET does not exclude a structural abnormality; imaging can be useful when obstructed-evacuation symptoms remain unexplained.[1]
  • Assesses levator ani muscle defects with high interobserver reliability on static T2-weighted images.[13]
  • Post-defecation straining identified additional/maximal anterior and middle descent in a retrospective 65-patient study. It supplements, rather than replaces, adequate evacuation images.[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 AssessmentKey StrengthsKey Limitations
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; essential for sphincteroplasty planningOperator-dependent; defect presence does not predict symptom severity; does not assess dynamic function
Fluoroscopic DefecographyStructural + functional — evacuation dynamics, prolapseSeated position (physiologic); detects occult enteroceles, intussusception, sigmoidocelesRadiation exposure; limited soft-tissue contrast
MRI DefecographyStructural + functional — multicompartment prolapse, levator anatomyNo radiation; comprehensive 3-compartment assessment; levator-muscle evaluationSupine position may underestimate posterior pathology; less available; more expensive

Per the ACG and ASCRS guidelines, the typical evaluation pathway is:[1][13][2]

  1. ARM + BET as initial testing when conservative management fails.
  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.
  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. Physiologic testing should answer a clinical question; ARM is not mandatory before every prolapse operation.[2][5]

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. 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.