MR image analysis
Pelvic MRI was performed with a 1.5-Tesla magnet (Sigma, General
Electric Medical System, Milwaukee, WI, USA) in the supine position, and
no vaginal or rectal contrast was used. The MRI measurements were
performed using WebViewer (Greenlander Information Technology, Version
1.0.0.53449). The measurements were performed on the midline or almost
midline sagittal plane with a fat-saturated T2-weighted fast recovery
fast spin-echo with a repetition time (TR) of 4100-4200 ms and an echo
time (TE) of 102-109 ms by a gynaecologist-obstetrician and a
radiologist, and any disagreements were discussed. The observers were
blinded to the clinical findings, but the patients’ ages were not
concealed.
The sagittal schematic of the pelvis demonstrates the following
anatomical landmarks (Fig. 1). Point P represents the most inferior
aspect of the pubic symphysis. Point B represents the bladder neck.
Point C represents the most distal
edge of the cervix. Point D represents the apex of the tented up
posterior fornix.
Two distinct reference lines were used to complete the MRI measurements
(Fig. 1). One line was drawn from point P to the midpoint of the third
sacral vertebra; we developed and named this line PS3L. The other line
was the pubococcygeal line (PCL), which was drawn from point P to the
last coccygeal joint3.
Points D and C were expected to represent the apical and middle parts of
the upper two-thirds of the vagina, respectively. Regarding the distal
part, a line was drawn perpendicular to the PS3L from point B; we
continued this line into the vaginal area, and the midpoint of the
vaginal portion of this line was named point b (Fig. 1A and B). The
perpendicular distances from points D, C and b to the PCL and PS3L were
measured (Fig. 1B).
The angle between the axis of the upper two-thirds segment of the vagina
(a line running through point D to point b) and the PS3L and PCL and the
angle between the PCL and PS3L were also measured (Fig. 1C).
Regarding the position locations of points D, C and b relative to the
PS3L, a line was drawn perpendicular to the PS3L from points B, C and D,
and the points of intersection of the two vertical lines were named b’,
c, and d. The distances from point P to points b’, c, and d were named
Pb’, Pc, and Pd, respectively (Fig. 1D).
The measurements were performed in centimetres or degrees. If an
anatomical landmark or angle was located above a reference line, it had
a positive value, and if it was located below the reference line, it had
a negative value.