MR defecography: prospective comparison of two rectal enema compositions

The objective of our study was to compare intraindividually two rectal enema compositions in MR defecography.

Twenty patients underwent MR defecography twice on a 0.5-T open-configuration system in the sitting position. During the first imaging session, MR defecography was performed with a rectal enema consisting of potato starch mixed with gadolinium (PS group). During the second session, the enema consisted of ultrasound gel mixed with gadolinium (US group). The imaging protocol consisted of midsagittal T1-weighted gradient-recalled echo MR images obtained at rest, at maximal sphincter contraction, at straining, and during defecation. All images were analyzed quantitatively by measuring the contrast-to-noise ratio (CNR) and reviewed by three independent observers with regard to the visibility of pelvic floor abnormalities and the extent of those abnormalities.

The CNR values in the PS group (mean +/- SD, 167.49 +/- 44.4) were significantly higher than those obtained in the US group (150.2 +/- 37.8) (p < 0.05). The visibility scores for anterior rectoceles and intussusceptions were higher in the PS group than in the US group (mean visibility scores: PS group, 2.8 +/- 0.42 and 2.6 +/- 0.56, respectively; US group, 2.3 +/- 0.77 and 2.2 +/- 0.74, respectively). The size and the number of incompletely emptying anterior rectoceles were higher in the PS group.

Ultrasound gel and potato starch provide good contrast and depiction of relevant pelvic floor abnormalities. However, the visibility of pelvic floor abnormalities and extent of those abnormalities depend on the composition of the rectal enema. In particular, the size and degree of anterior rectocele evacuation and intussusception size are often underestimated when ultrasound gel is used for rectal enema.