Magnetic Resonance Defecography Criteria for the Diagnosis of Dyssynergic Defecation

Background/Aims: Evidence regarding the diagnostic value of MR defecography (MRD) for confirming dyssynergic defecation (DD) is limited.We aim to evaluate the diagnostic performance of MRD parameters in identifying patients with DD.Methods: This retrospective study was conducted at a university hospital.Data from 235 consecutive adult patients with chronic primary constipation who underwent high-resolution anorectal manometry (HR-ARM), balloon expulsion test, and MRD between 2020 and 2024 were analyzed.The diagnostic performance of each dynamic MRD parameter was assessed using HR-ARM combined with balloon expulsion test as the reference standard.Results: A total of 109 participants (86 females; mean age 53.1 ± 15.3 years) were included, of whom 70 patients (64.2%) were diagnosed with DD.Quantitative dynamic MRD parameters, including the M-line, anorectal angle (ARA), and anal canal width (ACW), demonstrated significantly good discriminatory ability for differentiating patients with DD (all P < 0.05).At cutoff values of 2.0 cm for the M-line at defecation combined with prominent puborectalis muscle or abnormal evacuation of contrast during defecation, 1.6 cm for M-line change, 114° for ARA at defecation, -5° for ARA change, and 10 mm for ACW during defecation, these parameters demonstrated acceptable diagnostic performance, achieving optimal specificities (82.1% to 92.3%), positive likelihood ratios (3.66 to 7.06), and diagnostic odds ratios (8.25 to 14.25).Multivariate analysis identified ARA and ACW at defecation as independent diagnostic predictors of DD (P < 0.05).Conclusions: These findings support the establishment of practical and reliable MR defecography-based diagnostic criteria for patients with dyssynergic defecation.