How comparable is clinical grading of obstetric anal sphincter injury with that determined by four-dimensional translabial ultrasound?

Abstract

Objectives: To evaluate the agreement between grading of obstetric anal sphincter injuries (OASI) on translabial ultrasound (TLUS), using a newly developed algorithm, and grading on postpartum examination. A secondary aim was to assess the correlation between tear severity, as defined on ultrasound, and symptoms of anal incontinence and/or fecal urgency. Methods: This was a retrospective study of patients seen at a perineal clinic between 2012 and 2018, after recent primary repair of OASI. All patients underwent a standardized interview including the St Mark's anal incontinence test and four-dimensional TLUS. Post-processing of ultrasound volume data was performed blinded to all other data. Using tomographic ultrasound imaging, a set of eight slices was obtained, and the central six slices were evaluated for sphincter abnormalities. Slices with distortion, thinning or defects were rated as abnormal. The following algorithm was used to grade OASI: a Grade-3a tear was diagnosed if the external anal sphincter (EAS) was abnormal in < 4/6 slices; a Grade-3b tear was diagnosed if the EAS was abnormal in ≥ 4/6 slices; and a Grade-3c/4 tear was diagnosed if both the EAS and internal anal sphincter were abnormal in ≥ 4/6 slices. Clinical grading of OASI was determined according to the Royal College of Obstetricians and Gynaecologists guidelines. Agreement between clinical and TLUS diagnosis of OASI was evaluated using weighted κ. Results: Of the 260 women seen during the study period, 45 (17%) were excluded owing to missing data or a repeat OASI, leaving 215 complete datasets for analysis. The average follow-up interval was 2.4 months (range, 1–11 months) after OASI and the mean age of the women was 29 years (range, 17–42 years). One hundred and seventy-five (81%) women were vaginally primiparous. OASI was graded clinically as Grade 3a in 87 women, Grade 3b in 80, Grade 3c in 29 and Grade 4 in 19. On imaging, full agreement between clinical and TLUS grading was noted in 107 (50%) women, with a weighted κ of 0.398. In 96 (45%) women, there was disagreement by one category, with a weighted κ of 0.74 and in 12 (6%) there was disagreement by two categories. Twenty-four (11%) women were found to have a normal anal sphincter on imaging. Overall, potential clinical over-diagnosis was noted in 72 (33%) women and potential under-diagnosis in 36 (17%). The seniority of the diagnosing obstetrician did not significantly alter agreement between clinical and sonographic OASI grading (κ 0.44, 0.43, and 0.34, for specialists and senior and junior residents, respectively). The association between symptoms of anal incontinence and/or fecal urgency and TLUS grading did not reach significance (P = 0.052). Conclusions: Clinical and TLUS-based grading of OASI showed fair agreement. Clinical over-diagnosis may be increasingly common in our population, although under-diagnosis may still occur in a significant minority. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.