Magnetic resonance imaging with rectal Gd-DTPA: new tool for the diagnosis of perianal fistula.

This study investigated the effectiveness of magnetic resonance imaging (MRI) with rectal administration of the enteral contrast agent gadolinium diethylene triamine pentaacetic acid (Gd-DTPA) in the diagnosis of recurrent perianal fistulae, assessing the number, anatomical extent, location, and signal intensities of various lesions. Fistulas were examined by MRI before and after rectal administration of Gd-DTPA in 50 patients (excluding fistulas due to inflammatory bowel disease). Surgical findings were compared with both pre- and postcontrast T1-weighted, T2-weighted, and short T1 inversion recovery (STIR) sequences. Of the 68 fistulous tracts detected surgically, precontrast imaging identified 16 by T1-weighted images (hypointense), 27 by T2-weighted images (hyperintense or iso- to weakly hyperintense), and 54 by STIR. Postcontrast imaging identified 29 by T1-weighted images, 58 by T2-weighted, and 54 by STIR. MRI with rectal administration of Gd-DTPA thus facilitates determination of fistula tracts, which are better resolved by precontrast STIR than by either precontrast T1- or T2-weighted images. Postcontrast T2-weighted images were substantially superior to T1-weighted. Both noncontrast STIR and postcontrast T2-weighted sequences were adequate for classifying fistulas in ano, but in complex recurrent anal fistula postcontrast T2-weighted images were more helpful.