Two Cases of Low Intersphincteric Anal Fistulas with Intrafistulous Calculi

Anal fistulas with intrafistulous calculi are extremely rare. Enterolithiasis generally occurs due to the precipitation, aggregation, and calcification of non-digestible materials; however, its occurrence within anal fistulas remains poorly understood. Here, we report two cases of low intersphincteric anal fistulas with intrafistulous calculi, diagnosed via endoanal ultrasonography and treated surgically. We discuss the possible pathophysiological mechanisms, imaging characteristics, and clinical significance of these calculi.