Anterior Perineal Anus (Differential Diagnosis)

obst_19_n.jpg: Young infant with signs of constipation. A short and protruding perineum is obvious on inspection of the anus. The distance between the posterior commissure and the anterior rim of the anus amounts to less than 1 cm. The linea dentata is just recognizable while the posterior wall of the anus is slightly evaginated. The diagnosis is an anterior perineal anus (anterior ectopic anus) as cause of the constipation. The so-called Anus-Position-Index (= distance between the middle of the anus and the posterior commissure/distance between the tip of the coccyx and the posterior commissure) is less than 0.34 which means abnormal. (I owe this picture to K. Roth, Pediatric Surgery, CH- Aarau and Baden).