Comparison of dynamic magnetic resonance defaecography with rectal contrast and conventional defaecography for posterior pelvic floor compartment prolapse.

AIM: This study compared the diagnostic capabilities of dynamic magnetic resonance defaecography (D-MRI) with conventional defaecography (CD, reference standard) in patients with symptoms of prolapse of the posterior compartment of the pelvic floor.

METHOD: Forty-five consecutive patients underwent CD and D-MRI. Outcome measures were the presence or absence of rectocele, enterocele, intussusception, rectal prolapse and the descent of the anorectal junction on straining, measured in millimetres. Cohen's Kappa, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the positive and negative likelihood ratio of D-MRI were compared with CD. Cohen's Kappa and Pearson's correlation coefficient were calculated and regression analysis was performed to determine inter-observer agreement.

RESULTS: Forty-one patients were available for analysis. D-MRI underreported rectocele formation with a difference in prevalence (CD 77.8% vs D-MRI 55.6%), mean protrusion (26.4 vs 22.7 mm, P = 0.039) and 11 false negative results, giving a low sensitivity of 0.62 and a NPV of 0.31. For the diagnosis of enterocele, D-MRI was inferior to CD, with five false negative results, giving a low sensitivity of 0.17 and high specificity (1.0) and PPV (1.0). Nine false positive intussusceptions were seen on D-MRI with only two missed.

CONCLUSION: The accuracy of D-MRI for diagnosing rectocele and enterocele is less than that of CD. D-MRI, however, appears superior to CD in identifying intussusception. D-MRI and CD are complementary imaging techniques in the evaluation of patients with symptoms of prolapse of the posterior compartment.