Is two-dimensional oblique parasagittal ultrasound imaging valid for levator ani muscle assessment?

Objective: To evaluate the validity of two-dimensional (2D) oblique parasagittal ultrasound imaging to assess levator ani muscle avulsion. Methods: This was a cross-sectional prospective study of women attending a tertiary urogynecological service between February 2021 and August 2022. All women underwent a standardized interview, pelvic organ prolapse quantification (POP-Q) assessment and four-dimensional transperineal ultrasound. 2D oblique parasagittal ultrasound imaging was performed by rotating the transducer 10–20° from the midline to line up the main transducer axis with the fiber direction of the puborectalis muscle, followed by a full parasagittal sweep of the hiatus at rest. Postprocessing of archived ultrasound volume data was performed at a later date, blinded to all other data. Findings were compared with levator ani assessment results obtained previously using three-dimensional tomographic ultrasound imaging (TUI). Diagnosis of levator ani avulsion on TUI and oblique parasagittal imaging was analyzed for associations with pelvic organ prolapse (POP). Results: The datasets of 484 women were analyzed. Mean age was 58 (range, 16–94) years, mean body mass index was 30 (range, 17–65) kg/m² and mean parity was 2.6 (range, 0–8). POP symptoms were reported by 278 (57%) women. Clinically and sonographically significant POP was found in 385 (80%) and 350 (72%) women, respectively. Levator ani avulsion was diagnosed in 77 (16%) women on TUI and in 90 (18.6%) women on oblique parasagittal ultrasound imaging, with fair agreement between the two methods (Cohen's kappa of 0.365). There were significant associations between levator ani avulsion on 2D ultrasound imaging and POP diagnosis on clinical examination (odds ratio (OR), 2.88 (95% CI, 1.34–6.18); P = 0.005) and on ultrasound (OR, 2.92 (95% CI, 1.53–5.55); P = 0.001), but these associations were much stronger for TUI (P < 0.001 for both). Conclusion: There was limited agreement between tomographic and oblique parasagittal ultrasound diagnosis of levator ani muscle avulsion. The latter technique has some validity for levator ani assessment but is clearly less valid than TUI.