Abstract

Objective To evaluate the agreement between three-dimensional endoanal ultrasound (EAUS) and four-dimensional transperineal ultrasound (TPUS) in measuring anal sphincter defect angle. Methods This was a secondary analysis of the PERINEAL study, which evaluated the effect of perineal wound infection on anal sphincter integrity. Women were reviewed once a week, until their perineal wound had healed or for up to a maximum of 16 weeks. At each visit, both EAUS and TPUS (the latter at rest and on maximum pelvic floor muscle contraction (PFMC)) were performed to evaluate the presence of external (EAS) and internal (IAS) anal sphincter defect and measure the defect size. The largest angle size of a defect at the same sphincter level was analyzed. A defect was deemed significant if it was > 30°. Kappa coefficient (κ), intraclass correlation coefficient and standard error of measurement (SEM) were calculated, using EAUS as the reference standard. Results In 73 women scanned at weekly intervals, a total of 250 EAUS and 250 TPUS scans were performed. An EAS defect was found in 55 (22.0%) EAUS images and 47 (18.8%) TPUS images. An IAS defect was found in 26 (10.4%) images on both modalities. There was excellent agreement (κ = 0.87) between TPUS and EAUS in diagnosing the presence of an EAS defect and perfect agreement (κ = 1.00) in diagnosing the presence of an IAS defect. TPUS performed at rest had poor and moderate agreement with EAUS in measuring EAS and IAS defect size, respectively, with respective SEMs of ± 16.1° and ± 27.9°. TPUS performed during maximum PFMC had poor and moderate agreement with EAUS in measuring EAS and IAS defect size, respectively, with respective SEMs of ± 16.5° and ± 26.4°. Based on the SEMs, if the diagnostic cut-off of 30° for defect size on TPUS was used, an incorrect diagnosis of significant EAS defect could occur in approximately 9–36% of women and an incorrect diagnosis of a significant IAS defect could occur in approximately 4–15% of women, using EAUS as the reference. Conclusions This is the first study to compare directly anal sphincter defect angle measurements obtained on EAUS and TPUS. A cut-off angle of 30° should not be used for the diagnosis of a significant residual anal sphincter defect during TPUS examination. Further research is required to determine the optimal defect cut-off angle for TPUS.