Anterior and posterior compartment 3D endovaginal ultrasound anatomy based on direct histologic comparison

Abstract

We used direct histologic comparison to validate the use of 3D endovaginal ultrasound (EVUS) as a novel and emerging technology for evaluating the structures found in the anterior and posterior pelvic floor compartments. A young nulliparous female pelvis specimen was dissected and histologic slides were prepared by making 8-Micron-thick sagittal cuts. The slides were stained with Mallory trichrome and arranged to form large sections encompassing each anterior and posterior sagittal plane. Healthy nulliparous women underwent 3D EVUS to obtain 3D cubes of the anterior and posterior compartments. Two investigators independently evaluated the anterior and posterior midsagittal structures. The investigators mutually viewed the images and calculated urethral and anal sphincter measurements. Thirty-one nulliparous women underwent 3D EVUS; 77% of the participants were Caucasian, with mean age 31.8 [standard deviation (SD) 5.8] and mean body mass index (BMI) of 28.5 (SD 7.9). The following mean (SD) measurements were obtained: urethral length 36 mm (± 5); striated urogenital sphincter area 0.6 cm(2) (± 0.16); longitudinal and circular smooth muscle area 1.1 cm(2) (± 0.4); urethral complex width 14 mm (± 2); urethral complex area 1.3 cm(2) (± 0.4); internal anal sphincter length 26 mm (± 4); internal anal sphincter thickness 3.2 mm (± 0.8); and rectovaginal septum length 31 mm (± 5). The agreement for visualization of structures was as follows: vesical trigone 96% (κ = 0.65), trigonal ring 94% (κ = 0.8), trigonal plate 84% (κ = 0.6); longitudinal and circular smooth muscle 100%; compressor urethra 97% (κ = 0.85); striated urogenital sphincter 97% (κ = 0.85); rectovaginal septum 100%; internal anal sphincter 100%; external anal sphincter subdivisions 100%. Three-dimensional EVUS can be used to visualize structures of the anterior and posterior compartments in nullipara.