On pelvic reference lines and the MR evaluation of genital prolapse: a proposal for standardization using the Pelvic Inclination Correction System

Abstract

Five midsagittal pelvic reference lines have been employed to quantify prolapse using MRI. However, the lack of standardization makes study results difficult to compare. Using MRI scans from 149 women, we demonstrate how use of existing reference lines can systematically affect measurements in three distinct ways: in oblique line systems, distances measured to the reference line vary with antero-posterior location; soft issue-based reference lines can underestimate organ movement relative to the pelvic bones; and systems defined relative to the MR scanner are affected by intra- and interindividual differences in the pelvic inclination angle at rest and strain. Thus, we propose a standardized approach called the Pelvic Inclination Correction System (PICS). Based on bony structures and the body axis, the PICS system corrects for variation in pelvic inclination, at rest of straining, and allows for the standardized measurement of organ displacement in the direction of prolapse.

Positional pelvic organ prolapse (POP) evaluation using open, weight-bearing magnetic resonance imaging (MRI)

“…7 Standardization of dynamic MRI using reference lines has been a subject of interest to extend the concept of pre-and post-treatment aspects of the pelvic organs. 8,9 Supine MRI, with or without dynamic components, has helped us to understand both the anatomic relationships of the pelvic organs affected by prolapse and complications related to mesh insertion for treatment. However, limitations of evaluation of the pelvic organs in the supine position are recognized.…”

Standardization of dynamic magnetic resonance imaging measurements of pelvic organ prolapse: can the PICS line help?

“…Most of the available imaging systems are unable to demonstrate the full extent of POP because patients are examined in a supine position promoting current efforts to image patients in the sitting and upright position using open-magnet MRI units [1,[3][4][5]. In fact, sagittal plane images of women with POP that are commonly displayed in the literature as if taken in the upright position had been made in the supine position [6]. A further major problem with MRI studies of the pelvis is the incomplete reproducibility and lack of standardization of the patient effort exerted during straining [3][4][5].…”

“…Betschart et al review this topic further in a seminal Clinical Opinion [6]. The authors discuss the strengths and weaknesses of the current pelvic reference systems for dynamic MRI studies of POP.…”

“…Based on these findings, Betschart et al propose a standardized MRI measurement system for POP called the pelvic inclination correction system (PICS), which allows standardized measurement of organ displacement in the direction of prolapse by controlling for variation in pelvic inclination, at rest or straining, bony structures, and the body axis [6]. The hypothesis is biologically plausible since variations in pelvic inclination alter the direction of intraabdominal vector forces and the degree of transmission of abdominal pressure onto the pelvic floor, thereby influencing the development of pelvic floor weakness and subsequent prolapse [7].…”

“…Since the group published their first article about the standardized MRI investigation technique in 2001 [8], this contribution 12 years later shows how long the research process takes and how important the ongoing process of standardization of MRI measurements of POP is [6].…”