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.