To evaluate the agreement between two different imaging techniques, three-dimensional endoanal ultrasound (3D EAUS) and 3D/4D translabial ultrasound (TLUS), in detecting anal sphincter defects in women after primary repair of obstetric anal sphincter injuries (OASI). Correlation between the degree of anal sphincter defect on ultrasound and symptoms of anal incontinence was assessed.

This is a prospective cohort study of all primiparous women, referred to a perineal clinic between 2019 and 2021, after primary repair of OASI. Clinical grading of OASI was performed according to the classification described by Sultan (1). Patients completed a validated St Mark's anal incontinence questionnaire and underwent a clinical exam including a Pelvic Organ Prolapse Quantification (POP-Q), anal manometry, pudendal nerve terminal motor latency, anal endosonography and 3D/4D translabial ultrasonography. Assessment of ultrasound imaging was performed blinded to all other findings. Prior to ultrasound analysis, a test-retest series was carried out to evaluate inter-observer agreement for anal sphincter defect on TLUS (Cohen’s kappa value 0.92). Central six slices were evaluated for sphincter abnormalities on tomographic ultrasound imaging: 3a tear was diagnosed if <4/6 slices were abnormal at the external anal sphincter (EAS), 3b if EAS was abnormal in ≥4/6 slices and 3c/4th grade tears if both EAS and internal anal sphincter (IAS) were abnormal in ≥4/6 slices (2). A “residual defect” was diagnosed if a defect ≥ 30 degrees in 4 out of 6 slices from slices 2 to 7 on TLUS was noted (3). External and internal anal sphincter anatomy was assessed at upper, mid and lower anal canal on EAUS. Residual anal sphincter defects were recorded by determining the Starck Score: a series of measurements that determine the extent of a defect in the external and internal anal sphincters as well as the anal mucosa. The measurements include the length, depth and degree (angle) of the anal injury. Weighted κ was used to evaluate agreement between clinical, EAUS and TLUS diagnosis of OASI.

Of the 52 primiparous women referred to a perineal clinic after primary repair of OASI during the inclusion period, 25 (48%) were excluded due to missing data, mainly because of not attendance to their scheduled visit (21/25). Twenty-seven datasets were analysed at median follow‐up of 6 months (range 5–7months) after OASI. Mean age was 31 years (range 26–41 years). OASI was clinically graded as Grade 3a in 15 (55.5%), Grade 3b in 9 (33.3%), Grade 3c in 1 (3.7%) and Grade 4 in 2 (7.4%). Fifteen (55.5%) and 14 (51.9%) women were graded as Grade 3a, 8 (29.6%) and 9 (33%) as Grade 3b, 2 (7.4%) and 3 (11.1%) as Grade 3c or Grade 4 on TLUS and on EAUS, respectively (see table). One (3.7%) patient who was rated as a 3a tear clinically was found to have a normal anal sphincter on both TLUS as on EAUS imaging. Full agreement between clinical and TLUS grading was noted in 19 (70.4%) women, with a weighted κ of 0.60, and full agreement with EAUS grading in 18 (66.6%) women (weighted κ =0.62). Complete accordance between grading on EAUS and TLUS was noted in 18 women (66.6%) with a weighted κ of 0.61, (all p>0.05). In 9 (33.3%) women, there was disagreement by one category between EAUS-based and TLUS-based grading of OASI. There was no disagreement by two or more categories between both US-based grading techniques. Overall, potential clinical over‐diagnosis was noted in 6 (22.2%) and 5 (18.5%) women and potential under‐diagnosis in 2 (7.4%) and 4 (14.8%) women, on TLUS and EAUS, respectively. The association between symptoms of anal incontinence and TLUS grading did not reach significance (p = 0.35) at a median follow up of 6 months, nor did the association with EAUS (p=0.083). There was no significant correlation between Starck score on EAUS and St Mark score at a mean follow up of 6 months post oasis repair (p=0.96). Also, no significant association was found with residual defect on TLUS (p=0.88).

EAUS-based and TLUS‐based grading of OASI demonstrated moderate agreement (weighted κ=0.61). While clinical over‐diagnosis was encountered in one fifth of our population, under‐diagnosis was less common. The association between symptoms of anal incontinence and US grading did not reach significance. Another relevant constatation was that TLUS could not discriminate between 3c and 4th degree tears, while EAUS did. Almost 1 in 2 women did not attend their scheduled visit at the perineal clinic after OASI repair. This might possibly be due to low symptom bother postnatally and/or preoccupation with their newborn, however, it needs further investigation.

TLUS demonstrates a good alternative for grading of OASI compared to the ‘gold standard’ EAUS. This is relevant as it less invasive and more readily available.

Sultan AH. Obstetrical perineal injury and anal incontinence. Clin Risk. 1999; 5:193-6
Gillor M, Shek KL, Dietz HP. How comparable is clinical grading of obstetric anal sphincter injury with that determined by four-dimensional translabial ultrasound? Ultrasound Obstet Gynecol 2020;56(4):618-23
Guzmán Rojas RA, Kamisan Atan I, Shek KL, Dietz HP. Anal sphincter trauma and anal incontinence in urogynecological patients. Ultrasound Obstet Gynecol 2015; 46: 363–366.