(Poster 173) Standardizing Measurements to Define Uterine Version and Flexion on MRI Imaging

Objectives: While standardization exists for analyzing pelvic anatomy on MRI imaging, few measure uterine version and flexion. Version and flexion may be markers for other pelvic floor anatomy and function. Our aim was to develop a methodology for standardizing uterine version and flexion measurements on mid-sagittal MRI imaging to aid pelvic floor anatomy research.

Methods: Utilizing a preexisting MRI biorepository, mid-sagittal images were analyzed by two examiners using 3D Slicer with a third party available for judication. Four points (uterine fundus, internal cervical os, external cervical os, and introitus) were placed on mid-sagittal MRI images. Uterine fundus was defined as the apex of the uterine corpus along the axis of the endometrium. Internal os was defined as the point in the midline of the endometrial canal at the junction of the corpus and cervix identified through color and texture changes and at the point of maximal narrowing of the corpus. The external os was defined as the midline of the endocervical canal at the external surface of the cervix. The vaginal introitus was identified by drawing a horizontal line posteriorly from the inferior aspect of the pubic symphysis to the midpoint of the vaginal canal. Lines were drawn between the uterine fundus and internal os, the internal os and external os, and the external os and introitus to create the uterine body axis, cervical axis and vaginal axis, respectively. To determine uterine version, we use the cervico-vaginal angle made between the anterior aspects of the cervical and the vaginal axes (Figure 1). To determine uterine flexion, we use the cervico-uterine angle, the angle made between the anterior aspects of the uterine body and cervical axes (Figure 2).

Results: Cervico-vaginal angles < 180° are anteverted and angles >180° are retroverted. Cervico-uterine angles < 180° are anteflexed and angles >180° are retroflexed. For both measurements, angles at exactly 180° are defined as midline.

Conclusions: We developed a methodology using standardized, reproducible points on mid-sagittal pelvic MRI images to determine type and degree of uterine version and flexion.

Figure 1. Cervico-vaginal angle defining uterine version depicted in red. Angle formed by the cervical axis between the internal cervical os (yellow) and external cervical os (green) and the vaginal axis formed by the external cervical os (green) and introitus (purple). Anteversion with angle < 180° (1A). Retroversion with angle >180° (1B).
Figure 2. Cervico-uterine angle defining uterine flexion depicted in red. Angle formed by the uterine axis between the apex of the uterine fundus (blue) and internal cervical os (yellow) and the cervical axis between the internal cervical os (yellow) and external cervical os (green). Anteflexion with angle < 180° (2A). Retroflexion with angle >180° (2B).