Magnetic resonance imaging in anterior ectopic anus

Different criteria have been used in literature to describe the anterior ectopic anus (AEA) anomaly, resulting in uncertainty over its prevalence, association with constipation and definition of the indications for surgery. It has been recently proposed that the term AEA should be restricted to anomalies in which a normal appearing anal orifice is located in the perineum in a more anterior location than normal, with an anal canal of normal calibre that is shown by electrical stimulation to be surrounded by the voluntary external anal sphincter (EAS). We report about four infants, three females and one male, who presented with constipation and had an anteriorly located anal orifice of normal calibre. The anal position index measured clinically was less than 0.34 in all the female patients and 0.44 in the male patient. In preoperative magnetic resonance imaging (MRI), the EAS was distributed all around the circumference of the anal canal, including the ventral aspect of the anal canal, in all the patients. Preoperative MRI documentation of sphincter distribution is recommended for the diagnosis of AEA, as it would help in better definition of its association with constipation and the results of surgical management.