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Anorectal Function & Defecography

Three modalities — anorectal manometry (ARM), endoanal ultrasound (EAUS), and defecography (fluoroscopic and MRI) — serve complementary roles in the urogynecologic evaluation of pelvic-floor disorders, particularly defecatory dysfunction, fecal incontinence, and posterior-compartment prolapse. No single test is a gold standard; the ACG and ASCRS recommend interpreting results together, and the Rome IV criteria require at least 2 abnormal tests to confirm a defecatory disorder.[1][2]

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 — reflects internal anal sphincter tone (responsible for ~70% of resting continence).
  • Squeeze pressure increment — reflects external anal sphincter and puborectalis function.
  • Rectoanal gradient during evacuation (rectal pressure minus anal pressure) — the single best HRM predictor of defecatory dysfunction; 36% sensitive and 85% specific for prolonged balloon expulsion.[4]
  • RAIR — absent in Hirschsprung disease.
  • 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. Up to 37% of asymptomatic women demonstrate paradoxical pelvic-floor contraction during evacuation, underscoring the importance of clinical correlation.[1]

Indications in Urogynecology​

  • Defecatory dysfunction / obstructed defecation. ARM + balloon expulsion test (BET) is the recommended initial evaluation when conservative management (fiber, laxatives) fails. The probability of reduced rectal evacuation is 14% when both ARM gradient and BET are normal, 45% when either is abnormal, and 75% when both are abnormal.[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. ARM can identify dyssynergic defecation before prolapse surgery — unrecognized dyssynergia can lead to poor surgical outcomes and premature intervention.[5]
  • Guiding biofeedback. ARM is particularly useful for directing biofeedback therapy in patients with dyssynergic defecation, which is the only evidence-based treatment for functional defecatory disorders.[6][5]

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 detects occult sphincter defects in up to one-third of primiparous women after vaginal delivery, many of which are not clinically apparent. With 3D ultrasound, the prevalence of significant defects is approximately 10%.[7][1]
  • 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. EAUS can be used after perineal repair to evaluate residual injury and guide management in subsequent pregnancies, including early referral to specialized units.[9]

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). Strong correlation with EAUS scores (Spearman's ρ 0.74–0.77) and similar ability to predict fecal-incontinence symptoms. "Significant defects" on TPUS had an odds ratio of 46 for predicting anal incontinence, compared with 38 for EAUS.[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]

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 — approximately one-third of women with posterior vaginal-wall bulging have enteroceles or sigmoidoceles rather than rectoceles.[13]
  • Rectal prolapse
  • Perineal descent — observed in 44.4% of patients with chronic constipation.[2]
  • Dyssynergic defecation — failed or prolonged evacuation, paradoxical narrowing of anorectal angle.

A systematic review of >8,000 defecographies in constipated patients found high-grade intussusception in 23.7%, large rectoceles (>4 cm) in 15.9%, and enterocele descent in 16.8%.[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 (~4.9 mSv, approximately half of an abdominal / pelvic CT); 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. It is endorsed by the ACR, AUGS, IUGA, ASCRS, and SAR as one of the initial imaging tests of choice for suspected pelvic-organ prolapse and defecatory dysfunction.[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 — ~100° at rest, narrows to ~70° during Kegel, widens to ~120° during evacuation in healthy women; paradoxical narrowing during evacuation is the hallmark of dyssynergia.[5]
  • Levator-plate angle — assesses levator ani integrity.

Advantages over fluoroscopic defecography:

  • No radiation exposure.
  • Superior multicompartment assessment — simultaneously evaluates anterior (cystocele, urethral hypermobility), middle (uterovaginal prolapse), and posterior (rectocele, enterocele, intussusception) compartments.[15][13]
  • Detects >90% of large rectoceles, enteroceles, and peritoneoceles in patients with clinical features of defecatory dysfunction but normal BET.[1]
  • Assesses levator ani muscle defects with high interobserver reliability on static T2-weighted images.[13]
  • Post-defecation straining phase detects maximal prolapse in anterior and middle compartments.[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 weaknessHigh false-positive rate (37% of healthy women show paradoxical contraction); position-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.

Unrecognized dyssynergia in the setting of anatomic abnormalities can exacerbate symptoms, prompt premature surgery, and lead to poor long-term outcomes — making functional testing with ARM essential before proceeding to surgical correction of structural findings on defecography.[5]

Cross-references​

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