A simplified method for evaluating the anatomical axis of the upper two-thirds of the vagina on MRI: A hospital-based cross-sectional study

Backgrounds

Pelvic organ prolapse commonly affects the upper two-thirds of the vagina. However, evaluating this region in its normal position presents challenges. This study aimed to assess the anatomical axis of this vaginal segment using pelvic magnetic resonance imaging measurements.

Methods

A retrospective study of 614 hospitalized women from two hospitals, who were rigorously screened to exclude those with Pelvic Organ Prolapse or known anatomical variations (median age: 43 years, range: 17–76 years). Two reference lines were used: the pubococcygeal line (PCL) and a line from the inferior pubic symphysis to the third sacral vertebra (PS3L). Distances between the distal, middle, and apical points of the upper vagina and the reference lines, as well as the angles between the upper vagina and the reference lines, were measured. Comparisons were made among different age groups.

Results

The median distances from the distal, middle, and apical vaginal points to the PCL were 0.4 ​cm (interquartile range [IQR]: 0.0–0.7 ​cm), 2.1 ​cm (IQR: 1.7–2.5 ​cm) and 3.1 ​cm (IQR: 2.5–3.7 ​cm), respectively. The median PCL-vaginal angle was 29.0° (IQR: 23.0–34.0°). The median distances from the distal, middle, and apical vaginal points to the PS3L were -0.5 ​cm (IQR: -0.9–0.0 ​cm), 0.0 ​cm (IQR: -0.4–0.6 ​cm), and -0.2 ​cm (IQR: -0.9– 0.0 ​cm), respectively. The median PS3L-vaginal angle was 0.0° (IQR: -4.0–7.0°). Women aged 50 years or older had slightly lower vaginal points and slightly larger angles than younger groups in relation to both reference lines (p ​< ​.001). The vaginal axis in younger groups appeared parallel to the PS3L.

Conclusions

The axis of the upper two-thirds vagina was proximate to a line from the inferior pubic symphysis to the third sacral vertebra, particularly in younger women. It will likely become a simplified method for roughly assessing the vaginal axis in its situ at first glance.