Pelvic floor imaging with MR defecography: correlation with gynecologic pelvic organ prolapse quantification

Pelvic organ prolapse (POP) is assessed differently by gynecologists and radiologists. It is clinically staged by physical examination using the POP-Q (Pelvic Organ Prolapse Quantification) system and radiologically staged by modalities such as by Magnetic Resonance Defecography (MRD). The purpose of this study was to correlate the two methods of staging pelvic organ prolapse for each pelvic compartment by comparing correlative anatomic points and differences in technique. This understanding will help synthesize information from two different perspectives and bridge the gap between multiple specialists who participate in the care of patients with complex pelvic floor disorders.

A retrospective single institution study comparison of patients who underwent both dynamic magnetic resonance pelvic floor imaging and pelvic organ prolapse quantification (POP-Q) at our medical center was done. Two urogynecologists performed the POP-Q and one fellowship-trained radiologist interpreted the MRD and both staged pelvic organ prolapse independently.

A total of 280 patients underwent magnetic resonance imaging (MRI) of the pelvic floor from 1/2013 to 12/2017, of whom 68 met our inclusion criteria. When compared to POP-Q, MRI has strong, moderate, and weak correlation for quantification of anterior, middle, and posterior compartment prolapse, respectively. POP-Q measurements Aa, Ba, C, and D are analogous to true pelvic anatomical landmarks which are directly and consistently measurable by MRI, hence accounting for the better correlation in anterior and middle compartments when compared to measurements Ap and Bp which do not correlate with true anatomical landmarks, and hence can explain the weak correlation for posterior compartment prolapse.

When comparing POP-Q to MRI, anterior and middle compartment prolapse have better correlation than posterior compartment prolapse. Inherent differences that exist in technique and anatomic landmarks used for staging pelvic organ prolapse by clinical exam and imaging criteria account for this. MRD, however, still provides anatomic details on static images, real time simultaneous overview of multi-compartmental prolapse, characterizes contents of cul-de-sac hernias and rectal evacuation on dynamic imaging. Corroborative information derived from both methods of staging organ will result in optimum patient care.