Introduction and Hypothesis <p>The utility of magnetic resonance imaging (MRI) in recognizing the severity of pelvic organ prolapse (POP) in patients with rectal prolapse (RP) remains underexplored. Understanding POP volume in these patients may be crucial for targeted interventions, particularly in RP cases where a multidisciplinary approach is often required. This study investigates whether volume measurements via MRI defecography can improve screening for symptomatic POP and provide better guidance for clinical interventions.</p> Methods <p>This retrospective cohort study involved 77 women with RP who underwent MRI defecography at a university hospital from 2017 to 2022. Estimated levator ani subtended volume (eLASV) was calculated both at rest (eLASV-R) and during strain (eLASV-S), with multivariable regression analysis used to compare these measures. Youden’s index identified optimal cutoff values for high and low volumetric POP.</p> Results <p>Measurements of eLASV-S were predictive of symptomatic POP. The optimal cutoff for eLASV-S was 102.5 cm³, significantly associated with the need for surgical interventions. eLASV-S provided clearer differentiation between symptomatic and asymptomatic patients than eLASV-R.</p> Conclusions <p>Magnetic resonance imaging defecography, particularly eLASV-S measurements, appears valuable for identifying high-volume POP in patients with RP. The finding of a significant eLASV-S cutoff suggests that MRI volume assessments could assist in guiding clinical decisions. Prospective studies are recommended to further validate these results and explore the full diagnostic potential of MRI.</p>