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.