Reliability of 2D vs 3D Ultrasound for Evaluation of the Levator Ani Muscles

Objectives: Many providers have access to 2D ultrasound only. Although physical examination provides essential information about the pelvic floor, it can be useful to complement the history and physical examination findings with a point-of-care 2D ultrasound to evaluate levator ani integrity and function. We hypothesized that 2D perineal ultrasound (TPUS) in coronal view was able to visualize the levator ani muscle subdivisions (Puborectalis, PR, pubococcygeus, PC, and the iliococcygeus, IC) and measure their thickness. The primary aim of our study was to compare 2D TPUS measurements to 3D endovaginal ultrasound (EVUS) measurements in the same patients.

Methods: In this retrospective descriptive study, we compared visualization of the iliococcygeus, pubococcygeus, and puborectalis muscles using TPUS and EVUS in patients from our ultrasound database with various pathologies. The muscle was assessed, and if visible, the muscle thickness was recorded at three coronal levels: 1: mid-urethra; 2: mid-vagina; 3: mid-rectum (Fig. 1, 2). The muscle measurements between the two modalities were compared as continuous and discrete variables, and the positive and negative predictive value of 2D TPUS was calculated.

Results: The data of 46 women met the inclusion criteria. The patients had the following characteristics: 65% White, age 41+11, multiparous (mean parity of 2). The main complaint was parity-related changes/obstetric injury (36%), followed by prolapse (21%). Mean POPQ measurements are described in Table 1. The EVUS minimal levator hiatus (MLH) was 11.8+3. 2D TPUS did not visualize the pubococcygeus and iliococcygeus in any patients 0/46. When visualized, the puborectalis thickness on 2D vs. 3D were as follows: Right, 3.22±3.39 vs. 2.70±2.35, 4.01±3.60 vs. 4.32±2.99, 5.17±3.22 vs. 4.74±2.90, Left, 3.25±3.43 vs. 2.55±1.85, 4.20±3.68 vs. 4.74±2.57, 5.90±3.64 vs. 5.81±2.45 on levels 1, 2, 3 respectively (Table 2). The positive predictive value of TPUS for visualizing the puborectalis muscle on levels 1, 2, and 3 were 0.82, 0.75, and 0.86 for the right side and 0.70, 0.74, and 0.84 for the left side, respectively. The negative predictive value of TPUS for visualizing the puborectalis muscle on levels 1, 2, and 3 were 0.89, 0.77, and 0.5 for the right side and 1, 1, and 0 for the left side, respectively.
Using 3D EVUS measurements as a reference, the 2D ultrasound visualized the levator ani muscles in coronal levels 1, 2, and 3 at 89%, 84%, and 100% on the right side and 69%, 73%, and 90% on the left side, respectively.

Conclusions: 2D TPUS may act as a screening tool for visualization of the puborectalis muscle in the absence of 3D ultrasound. The attachment point of the puborectalis muscle to the levator ani enthesis at the pubic bone (level 1) is difficult to visualize by 2D ultrasound, which creates a challenge for the diagnosis of levator ani avulsion.