Does exclusion of subcutaneous external anal sphincter on exoanal imaging matter?

Abstract

There is some speculation that an intact distal anal sphincter complex is of decisive importance for continence, although the external anal sphincter (EAS) is considered to be a single functional and anatomical entity. On tomographic translabial ultrasound (TLUS), the caudal slice at the level of the subcutaneous EAS is currently omitted from the diagnostic algorithm due to the prevalence of artifact at that level. The aim of this study was to determine the predictive value of assessment of the subcutaneous EAS on tomographic TLUS for anal incontinence (AI). This was a retrospective study of 463 women seen at our urogynecological service in 2015. All underwent a standardized questionnaire, including determination of St Mark's incontinence score (SMIS), clinical examination and three-/four-dimensional TLUS. On tomographic TLUS, EAS defect angles in slices one to seven were measured on maximum pelvic floor muscle contraction. A slice was defined as positive for a defect if the defect angle was ≥ 30°. The association between significant subcutaneous EAS trauma (i.e. defect angle of ≥ 30° in slice seven) and symptoms of AI, symptom bother score and SMIS was assessed. The performances of the standard six-slice model and the seven-slice model, including the subcutaneous EAS, in the prediction of AI were compared. While there was a highly significant association between all measures of AI and significant EAS trauma in slice seven, addition of the seventh slice to the existing six-slice model did not improve the predictive value for AI. As inclusion of the subcutaneous slice of the EAS on tomographic TLUS does not seem to improve the predictive value for AI, the current methodology for assessment of EAS trauma on tomographic TLUS can remain unchanged. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.