Interpretation
Several reference lines have been proposed to stage POP on MRI, but to
the best of our knowledge, no reference lines represent the axis of the
normal vagina9,10. In this study, we compared the PS3L
with the pubococcygeal line (PCL). The PCL is the most widely used and
recommended reference line for POP staging with
MRI3,9. Traditionally, in situations in which the
bladder neck and vaginal vault or distal edge of the cervix descend
below the PCL on MRI, the diagnosis of prolapse is
established3. As shown in this study, the PCL was
under the vaginal axis, which is consistent with previous
studies3,9. In fact, the PCL was thought to
approximate the axis of the levator plate18. Other
lines, such as the midpubic line and the perineal line, were introduced
and were expected to correspond to the level of the
hymen19,20. The hymen is the fixed reference point
recommended by the International Continence Society and is used by
urogynaecologists to stage POP11. Clinically,
successful surgical treatment for prolapse from an anatomical
perspective has been defined as no apical descent greater than one-third
into the vaginal canal or anterior or posterior vaginal wall beyond the
hymen21. However, the plane of the hymen is anterior
to the pubic bone and crosses the urethral meatus4.
Evaluations of POP based on these lines are not in situ assessments and
could result in underestimation, further leading to incomplete or
incorrect surgery. Nearly one-third of patients undergoing surgery for
POP repair were estimated to require reoperation within 4 years after
the initial surgery22. After prolapse surgery, new
pelvic floor symptoms may develop, while preexisting pelvic floor
symptoms may improve, worsen, or remain unchanged21.
In this study, the measurements based on the PS3L showed superiority
over those based on the PCL because they were more concentrated, that
mainly because relative to the PCL, the PS3L has an orientation that
mostly conforms to the normal vaginal anatomy, and in situ evaluation
may reduce deviations to a certain degree. Therefore, quantifying POP
based on the PS3L may be more likely to allow quantification and grading
of the extent of POP.
However, the measurements still showed variation in these parameters,
even in the young women, possibly because the uterosacral ligament is
attached anteriorly mostly but not exclusively on the posterior aspect
of the cervicovaginal junction23, posteriorly broadly
to the first three sacral vertebrae and variably to the fourth sacral
vertebra24. In addition, the definitive role of
paravaginal support in the middle third of the vagina and its
contribution to the development of prolapse are still
unknown25,26. In this study, the vaginal points in the
elderly women were slightly lower than those in the younger women.
Ageing, multiparity, and especially previous vaginal delivery are high
risk factors for POP27, and a moderate degree of
prolapse in continent women based on MRI has been reported due to its
ability to measure actual pelvic organ descent19,28.
However, in most cases, overall, as shown in this study, the PS3L may
represent the axis of the normal upper two-thirds of the vagina