PC line versus H line as MR defecography reference for bladder descent

Objectives: MR defecography imaging has been used widely to study pelvic floor function and diagnose pelvic organ prolapse (POP). Prior studies have shown that pelvic floor and organs normally endure synchronized and wide range of motion during strain and defecation which can be exaggerated in parous women but still normal and without any clinical vaginal prolapse. The aim of this study was to investigate the diagnostic accuracy of H line to detect bladder descent compared to current landmark PC line.

Methods: In this retrospective cohort study, data of patients who underwent MR defecography in our medical center and were diagnosed with moderate to severe bladder descent by radiologic measurements were recruited. One rest image and one maximum evacuation image for each subject were used for the following measurements: Bladder base perpendicular distance from: 1) genital hiatus indicative of clinically significant bladder descent, 2) Pubococcygeal line as current radiological reference line, and 3) H line or minimal levator hiatus line indicative of pelvic floor muscle and connective tissue support (Figure 1).

Subjects were categorized as clinically significant bladder descent if “bladder base” reached within 1 cm or lower of the genital hiatus. Three statistical methods were employed to examine the differences and predictive capabilities of the three reference lines relative to the GH measure. An ANOVA was performed to evaluate differences in demographics, symptoms, and MRI measures. Univariate linear regressions were conducted using the continuous distance of the bladder from the GH on the bladder descent group. Finally, ROC analysis was performed using the same groups established in the ANOVA.

Results: Seventy subjects were included, 30 with clinically significant bladder descent based on distance to GH. Women with bladder descent were older (64.0 ± 11.8 vs. 51.2 ± 15.6, p< 0.001), had increased parity (3 (1-7) vs. 2 (0-5), p=0.009) and had a more descended bladder compared to the H line at rest (1.9 ± 0.5 vs. 2.2 ± 0.4, p=0.003) and evacuation (­2.4 ± 1.6 vs. ­0.7 ± 1.1, p< 0.001). The univariate and multivariable logistic regression data is summarized in Table 1, showing that the H line referenced measurement remained the best predictor of clinically significant bladder descent. ROC analysis was used to identify measurement threshold to diagnose clinically significant bladder descent for both measurements, Bladder base H line (­1.2 (80.0, 72.5) AUC 0.82 ), and bladder base PC Line (3.3 (77.8, 79.5), AUC 0.86).

Conclusions: Our data supports the application of minimal levator hiatus plane and specifically H line as reliable landmark to diagnose bladder descent using MR defecography imaging. The current bony landmark used (PC line) does not accommodate for pelvic floor change in shape and motion induced by childbirth and results in overdiagnosis of POP and possible unnecessary treatments.