Endocoil magnetic resonance imaging quantification of external anal sphincter atrophy

Anal function depends on the integrity and quality of the sphincter muscles . The diagnosis of external anal sphincter atrophy on endocoil magnetic res onography has been associated with poor outcome from sphincter repair, alth ough the imaging criteria for atrophy remain unclear. Women with intact sphincters on endosonography and either normal (more than 60 cmH(2)O) (n = 9) or low (n = 16) squeeze pressures had endocoil magneti c resonography and electromyography. The area and fat content of the extern al anal sphincter and puborectalis were measured on mid-coronal magnetic re sonography and images were graded as showing normal, intermediate or advanc ed atrophy. The definition of the external anal sphincter on endosonography and the thickness of the internal anal sphincter were also assessed. Women with a normal anal squeeze pressure had a larger external anal sphinc ter cross-sectional area (mean(s.d.) 240(56) versus 193(62) mm(2); P = 0.01 ) with a lower mean fat content (mean(s.d.) 23(4) versus 30(6) per cent; P < 0.001) than those with low squeeze pressures. There was an overall correl ation between squeeze pressure, cross-sectional area (r = 0.32, P = 0.02) a nd fat content (r = - 0.51, P < 0.001). Patients with a thin (less than 2 m m) internal anal sphincter and/or a poorly defined external sphincter on en dosonography were more likely to have atrophy (positive predictive value 74 per cent). Potential endosonographic markers for external anal sphincter atrophy are s uggested, and a visual scale for endocoil magnetic resonographic assessment has been validated.