MAGNETIC-RESONANCE-IMAGING OF THE ANAL-SPHINCTER USING AN INTERNAL COIL

A surface coil placed within the anal canal was used to image the anal sphincter and determine normal anatomy and contrast enhancement patte rns as well as appearances in disease. Sixteen normal volunteers and 2 4 patients were examined. Imaging was performed on a 0.5-T Picker Asse t and a 1.0-T Picker HPQ Vista MRI scanner. T1-weighted and T2-weighte d spin-echo, T1-weighted gradient-echo, STIR images transverse to the sphincter, and T1-weighted spin-echo images parallel to the sphincter in the coronal oblique plane were obtained. Intravenous gadopentetate dimeglumine (0.1 mmol/kg) was given to two normal subjects and 10 pati ents. The coil was easy to insert and well-tolerated and provided high spatial resolution. The internal sphincter had a higher signal intens ity than the external sphincter on ah sequences but particularly on ST IR images. Brisk contrast enhancement of the internal sphincter was se en. Sphincteric abscesses and fistulous tracks were identified in thre e patients and confirmed at surgery. Sphincter defects were seen in th ree patients with obstetric trauma, and these were confirmed at surger y. Sphincter atrophy was seen in four patients with idiopathic fecal s oiling. High resolution magnetic resonance imaging with a dedicated en doanal coil provides excellent visualisation of normal anatomy and pat hology in and around the anal sphincter and may be of considerable val ue in diagnosis.