Comparing 3-Dimensional Ultrasound to 3-Dimensional Magnetic Resonance Imaging in the Detection of Levator Ani Defects

Objective The aim of this study was to compare the detection of levator ani defects (LAD) between 3-dimensional (3D) ultrasound (US) and 3D magnetic resonance imaging (MRI). Methods This is a secondary analysis of the Pelvic Floor Nerve Injury Following Childbirth Study. Nulliparous women underwent a standardized protocol of pelvic floor evaluations between January 2008 and December 2013, prior to pregnancy (V1) and at 2 points postpartum: 6 weeks (V2) and 6 months (V3). Those women who underwent a high-resolution 3D MRI pelvic floor sequence were selected. Comparisons were made to concomitantly acquired 3D perineal US. Eight tomographic slices were examined in the axial plane, each side independently scored with 0 (no defect) or 1 (defect). A similar tomographic approach was applied to the MRI. For both MRI and US, the right and left sides were each scored. A total score of 0 to 8 was given to each side. A dichotomous variable "complete LAD" was defined. Cohen κ was used as a measurement of agreement of complete LAD between MRI and US. Kendall τ b was used to correlate total scores. Results On the right side, 80 (90%) of 89 pairs were in agreement (concordant in the diagnosis or not of a "defect"). On the left side, 72 (81%) of 89 pairs were in agreement. Correlations (Cohen κ) of complete LAD were 0.65 (P < 0.001) on the right and 0.37 (P < 0.001) on the left. Correlations of total scores were 0.47 (P < 0.001) on the right and 0.41 (P < 0.001) on the left. Conclusions Moderate agreement was found between 3D US and 3D MRI LAD detection. More LADs and discordance were seen on the left.