A new reference line for the evaluation of the normal position of the
upper two-thirds of the vagina based on MRI: a retrospective study.
Objectives The upper two-thirds of the vagina is most commonly affected
by pelvic organ prolapse. This study aims to find a reference line
proximate to the axis of this part of the vagina on MRI which is
critical but lacking. Design Retrospective cross-section study Setting
Two university-affiliated hospital in China (July 2018 - June 2019)
Population Six hundred and fourteen women without prolapse Methods Two
reference lines were introduced to compare with the upper two-thirds of
the vagina on pelvic MRI: the pubococcygeal line (PCL) and a line
passing through the inferior pubic symphysis to the midpoint of the
third sacral vertebra (PS3L). Main outcome measures The distances and
the angles between the vagina and both reference lines were measured.
Results: The median distances from the distal, middle, and apical points
to the PS3L were -0.5[interquartile range (IQR), -0.9 - 0.0] cm,
0.0[IQR, -0.4 - 0.6] cm, and -0.2[IQR, -0.9 - 0.0] cm,
respectively, while the median distances to the PCL were 0.4[IQR, 0.0
- 0.7] cm, 2.1[IQR,1.7 - 2.5] cm, and 3.1[IQR, 2.5 - 3.7] cm,
respectively. The median angle between the vagina and the PS3L was
significantly smaller than that with the PCL (0.0[IQR, -4.0 - 7.0]
degree vs 29.0[IQR, 23.0 - 34.0] degrees, p<.001).
Conclusions: A line passing through the inferior portion of the pubic
symphysis to the third sacral vertebra mostly conforms to the normal
upper two-thirds of the vaginal axis.