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

Abstract

Dynamic magnetic resonance imaging (MRI) of the pelvis has been rapidly introduced into urogynecological research and practice in recent years mainly to address the shortcomings of clinical assessment systems in women with pelvic organ prolapse (POP). The primary objective was to better select candidates for surgical intervention and choose the appropriate procedure in order to reduce recurrences by allowing accurate identification and objective measurement of prolapse and simultaneous topographic assessment of the pelvis at rest and straining [1–5]. MRI is particularly indicated in women with multi-compartment POP and in those who had undergone previous repair, as imaging can reveal more extensive prolapse than physical examination alone with detection rates similar to other conventional fluoroscopic and ultrasound methods [1, 3, 4]. Staging of POP using MRI has also been suggested by measuring the perpendicular distance between several reference points and lines in each compartment at rest and after straining [1–5]. The two most commonly used lines are one connecting the inferior aspect of the pubic symphysis to the last coccygeal joint, the pubococcygeal line (PCL), and one extending caudally along the long axis of the symphysis pubis, the midpubic line (MPL). Several MRI staging systems have been published for both of these lines [1, 3, 4]. Despite the widely accepted role of MRI in supplementing clinical evaluation and management of women with POP, this imaging modality has certain limitations. Most importantly, so far, there has been no standardized technique for performing MRI examination of the pelvis. Imaging protocols vary according to patient positioning, filling media, pelvic organ opacification, patient maneuvers (i.e., rest, Kegel, Valsalva, evacuation) and MRI sequences and planes [1–5]. 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, 3–5]. 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 [3–5]. The anatomical landmarks used for pelvic measurements are easily identified inMRI and this is expected to increase the validity of measurement [5]. The intraand inter-observer reliability of most MRI measurements is, however, rarely described in POP studies [2]. Furthermore, the reference line used for MRI interpretation of POP is not consistent in all studies as this is often based on radiologist experience and referring physician preference [1, 5]. In a recent systematic review, seven different reference lines in relation to a wide variety of reference points have been used in different studies with imprecise definition or interchangeable use of some lines, e.g. “MPL/hymenal line” and “PCL/sacrococcygeal inferior pubic point line” [2]. Although the MPL corresponds anatomically to the level of the hymen on cadaveric dissection, the landmark used for clinical staging of POP, the reliability of MRI using the MPL versus clinical findings in women with POP was lower than that of the PCL in most reports [1, 2]. It is obvious that we lack a proper validation system for interpreting MRI measurements of POP and we urgently need to reach a consensus on a more standardized and scientifically robust MRI protocol for examination of the pelvis. Betschart et al. review this topic further in a seminal Clinical Opinion D. E. E. Rizk Department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University, Cairo, Egypt