Tweetable abstract:
A line passing through the pubic symphysis to the third sacral vertebra
mostly conforms to the normal upper two-thirds of the vaginal axis.
Introduction
Pelvic organ prolapse (POP) is a common, distressing
condition1. An objective and accurate evaluation of
POP is important for diagnosis and treatment, but physical examinations
remain limited to anatomical assessments2. MRI with
high soft-tissue resolution provides a multiplanar depiction of the
pelvic anatomy and has been considered a promising complementary
diagnostic tool3-8, but its validation is
unsatisfactory9-10. As POP is clinically defined as
the descent of the anterior, apex, or posterior vaginal
walls11, an in situ reference line for evaluating the
vagina is critical but lacking 9-10.
An assessment of the vagina in situ requires an understanding of its
supporting structures, which have been divided into three
levels4, 12. The upper third of the vagina is
typically considered to be suspended by the cardinal and uterosacral
ligaments12, 13. However, the role of the cardinal
ligament is controversial but was proven to be a mesentery structure
consisting of vessels and nerves14,15. The main
ligament-like structure of the upper third seems to be the uterosacral
ligament. In the middle third of the vagina, the anterior surface of the
vagina and its lateral attachment to the arcus tendineus fasciae of the
pelvis form the pubocervical fascia 12. In the lower
third of the vagina, the pubocervical fascia continues anteriorly,
merges with the urethra and then attaches to the pubic symphysis. The
attachments in the lower third are highly dense such that the lower
portion seldom suffers from POP12. In summary, the
upper two-thirds of the vagina are more commonly clinically and
anatomically affected by POP, and to our understanding, the structure
seems to be mainly supported by the uterosacral ligament, which extends
from the second to the fourth sacral vertebra region to the dorsal
margin of the uterine cervix and/or the upper third of the posterior
vaginal wall13, and by the pubocervical fascia, which
originates from the anterior surface of the vagina and anteriorly ends
at the pubic symphysis12. Therefore, we speculate that
a line passing through the
inferior aspect of the pubic symphysis to the third sacral vertebra
might be the closest proxy for the
normal upper two-thirds of the vaginal axis (Fig. 1A). Therefore, this
article reviews the vaginal anatomic structures of women without POP and
analyses the relationship between this line and the vagina on sagittal
MR images.