3D-TPU assessments
The same investigator (H.N.O), blinded to clinical and fundal pressure data, performed all the ultrasound volume acquisitions within 48 h of delivery, using a GE Voluson E6 (GE Penta Healthcare) with a 2–8-MHz convex volume, real-time 4D transducer. A thin film covered 4D probe placed on the perineum transversely, with light touch oriented postero-inferiorly to anal canal. Pelvic floor imaging settings were chosen, acquisition angle was set to 60° or 70°, the image quality settings and harmonics increased to maximum for optimization of resolution.
Tomographic ultrasound imaging (TUI) on maximum pelvic floor muscle contraction was used to assess the entire external and internal anal sphincter as described by Dietz et al.11 Six slices, at 2 mm slice intervals, were created in the axial plane, from at the level of the subcutaneous portion of EAS to at the level of anorectal junction, cranial to IAS. The AS was evaluated in 6 central slices and sphincter defect was diagnosed as a discontinuity of the ring shape of the EAS and IAS, appearing hypoechoic in IAS relative to the EAS and hyperechoic relative to the IAS in EAS. A complete AS defect has been defined as a defect of 30° or greater in circumference of AS in at least 3 slices (Figure 1). Incomplete defect described when less than 3 and/or partial discontinuity occurs in EAS or IAS (Figure 2). Other signs; thinning of EAS and/or IAS, thinning of EAS and/or IAS, thickening of the IAS opposite the defect, “halfmoon sign” were used indicate defect of AS (Figure 3). Half moon sign describes thickening of the IAS opposite the rupture site, with thinning or interruption in the area of repair.13 Analysis of stored volumes was conducted offline using 4D VIEW version 10.2; GE Healthcare, London, UK. An interobserver test–retest series was conducted for complete IAS and EAS defect on the volumes recorded for the first 20 patients recruited for this study.