Comparison of 3D endoanal ultrasound and external phased array magnetic resonance imaging in the diagnosis of obstetric anal sphincter injuries

Jaan Kirss,Tarja Pinta,Mikael Victorzon,Marja Kallio-Packalen,Jyrki Ruohonen,Heikki Huhtinen,Eini Niskanen,Sarita Victorzon

doi:10.1007/s00330-019-06125-8

Abstract

ObjectivesThe gold standard of postpartum anal sphincter imaging has been the 3D endoanal ultrasound (EAUS). Development of magnetic resonance imaging (MRI) has allowed anal sphincter evaluation without the use of endoanal coils. The aim of this study is to compare these two modalities in diagnosing residual sphincter lesions post obstetric anal sphincter injury (OASI).MethodsForty women were followed up after primary repair of OASI with both 3D EAUS and external phased array MRI. Details of the anal sphincter injury and sphincter musculature were gathered and analysed.ResultsThere was a moderate interrater reliability (κ = 0.510) between the two imaging modalities in detecting sphincter lesions, with more lesions detected by MRI. There was a moderate intraclass correlation (ICC) between the circumference of the tear (κ = 0.506) and a fair ICC between the external anal sphincter thickness measurements at locations 3 and 9 on the proctologic clock face (κ = 0.320) and (κ = 0.336).ConclusionsThe results of our study indicate that the use of external phased array MRI is feasible for detecting obstetric anal sphincter lesions postpartum. This allows for imaging of the sphincter defects in centres where EAUS imaging is not available.Key Points• A two centre prospective study that showed external phased array MRI to be a valid imaging modality for diagnosing obstetric anal sphincter injuries.

Highlights

The main aetiological factor associated in developing faecal incontinence (FI) is vaginal birth
There have been studies evaluating the correlation of endoanal ultrasound (EAUS) with endoanal MR imaging on diagnosing sphincter lesions [20], there have been no studies comparing external phased array magnetic resonance imaging (MRI) and 3D EAUS imaging in diagnosing postpartum obstetric anal sphincter injury (OASI)
Studies where EAUS imaging is compared to endoanal MRI show that EAUS is superior in diagnosing IAS defects, endoanal MRI is as sensitive in diagnosing EAS defects [20, 26, 27]

Summary

Introduction

The main aetiological factor associated in developing faecal incontinence (FI) is vaginal birth. The aetiology of postpartum FI is multifactorial, with injury to the anal sphincters as the principal cause. Injury to the pudendal nerve, puborectalis muscle, the anal sphincter complex, or the combination of these factors could play a role in developing postpartum FI [1,2,3]. Even after a successful initial repair of the sphincter lesion, women with obstetric anal sphincter injury (OASI) have a 50% greater risk of developing faecal incontinence compared to patients without such an injury [4, 5]. It has been reported that women with a history of OASI are less likely to plan future pregnancies [6,7,8]

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