Comparison of Surface and Saddle Endoanal Coil to Evaluate anal Sphincter in Infants and Young Children: Experimental Study Using Phantom and Cats

PURPOSE: We designed an inside-out-type endoanal surface and saddle coil to evaluate the anal sphincter of young children who have difficulty in controlling defecation after the correction of anorectal malformation, and compared two coils using an imaging phantom and cats. MATERIALS AND METHODS: Using two coils, T1- and T2-weighted axial and coronal images of the phantom and of the anorectal region of cats were obtained, and the results were compared in terms of changes in signal intensity and SNR according to the distance from the coil's surface. We also compared the capability of the coils to delineate the internal and external anal sphincter of cat anorectum, both of which are important in the control of defecation. RESULTS: The saddle coil was slightly superior to the surface coil in terms of SNR, but inferior in terms of the signal intensity of the region of interest of the cat's anorectum. Moreover, artifacts of low signal intensity appeared in an azimuthal direction on axial images acquired using the saddle coil and prohibited delineation of the whole of the anal sphincter. In terms of image quality, the surface coil was therefore superior to the saddle coil. CONCLUSION: Our findings suggest that among inside-out-type endoanal coils, the surface coil may be superior to the saddle coil in MR imaging to evaluate the anal sphincter of young children.

Usefulness of Preoperative MRI in Recurrent Anorectal Fistula

PURPOSE: To evaluate the usefulness of preoperative MRI in the patient with recurrent anorectal fistula. MATERIALS AND METHODS: Fourteen patients with recurrent anorectal fistula underwent non-contrast MRI. In eight patients, T1-, T2- and proton-weighted images were taken in the axial, coronal and sagittal planes, and T1- andT2-weighted images taken in the axial and coronal planes were obtained from the other six. RESULTS: Fourteen cases of anorectal fistula and eight cases in which there was a combined abscess were detected. Preoperative MRI clearly showed the exact anatomical relationship with the anal sphincter, levator ani and surrounding soft tissue. In two cases in which there was fibrous scarring of the fistula tract, low signal intensities were seen on all MRI sequences. Preoperative information in the group in which only axial and coronal T1- and T2-weighted images were obtained was sufficient. CONCLUSION: Preoperative MRI in patients with recurrent anorectal fistula or suspected multiple fistulous tracts provide objective information concerning the anatomical location and extension of a fistula and combined abscess and could thus reduce the reoperation rate. An understanding of pathologic state through MRI signal intensity can help decide the most appropriate course of treatment.