High resolution magnetic resonance imaging of the anal sphincter using an internal coil.

An internal receiver coil was used to obtain high resolution transverse and oblique coronal magnetic resonance images of the anal sphincter in five normal volunteers and five patients. The internal sphincter had a high signal intensity on T1 weighted, T2 weighted, and STIR sequences whereas the conjoined longitudinal muscle and external sphincter had a low signal intensity. The internal sphincter (but not the external sphincter) showed contrast enhancement after administration of intravenous gadopentetate dimeglumine. The oblique coronal plane was particularly useful for showing the thickness and the relations of the external sphincter. Sphincteric abscesses as well as muscle defects, hypertrophy, and atrophy were clearly shown. The coil was well tolerated by most subjects. It has considerable potential for improving the diagnosis of anorectal disease.