Morphometric Characterization of Levator Ani Subdivisions in Healthy Controls and Patients: An MRI Study Using 3D PICS.

Introduction and hypothesis: To date, levator ani muscle (LAM) morphometry has been classified descriptively and semi-quantitatively. New MRI techniques enabling detailed visualization with the 3D pelvic inclination correction system (3D PICS) could offer a one-stop-shop diagnostic modality for quantitative assessment of LAM subdivisions. The aim of this controlled MRI study was to assess morphometric LAM subdivision characteristics in two distinct groups of premenopausal women, namely nulliparous asymptomatic controls and symptomatic patients (Pelvic Organ Prolapse Quantification [POP-Q] ≥ II).

Methods: Magnetic resonance imaging scans of the 22 women in each group were analyzed applying the 3D PICS coordinate system. A second reading of MRI was used to calculate interrater reliability (IRR). Origins and insertions were expressed in the 3D-Cartesian coordinate system in relation to point 0/0/0 (inferior pubic point). Distances and angles between muscles and planes were described using mean and standard deviation or median with first and third quartiles for all LAM subdivisions.

Results: Moderate to good IRR was reported except for points close to point 0/0/0. Origins showed no difference between groups. Insertions differed notably in the vertically oriented pubovaginal, puboperineal, and puboanal muscles, with patients exhibiting lower positions along the superior-inferior axis by 6.1-7.7, 8.8, and 8.0-8.2 mm respectively. In contrast, the insertions of the horizontally oriented puborectal muscle showed a smaller difference of 1.8 mm. Muscle lengths were also 4% to 24% longer in cases.

Conclusions: This in vivo MRI study reveals first geometric 3D data on LAM morphology in 3D PICS for both cases and controls. Exact 3D coordinates of origin/insertion points, lengths, and angles could serve as a basis for future imaging-based POP diagnostics.