[Congenital anomalies of the anus and rectum].

There is confusion in the minds ofmany clinicians about the exact anatomical features of the individual lesions of anorectal anomalies and therefore about the way in which they should be treated. This arises partly because some, like the covered anus, are visible in the perineum, whereas in others part of the anomaly is visible, for example, in a low vaginal fistula, but the more important part, the blind end of the rectum, lies deep in the pelvis separated from the skin by the levator ani sheet of muscle. The indiscriminate use of the term 'imperforate anus' adds to the confusion because it implies that only the anus is abnormal and that the rest of the anal canal and rectum are unaffected. This term suggests that by incising the skin over the anus and cutting deep enough into the midline of the perineum the bowel can be opened and the obstruction relieved. As will be seen later, this term can properly be applied only to the so-called 'covered anus', and the other types should be classified anatomically according to their nature. Confusion also arises because of the misleading classification of these anomalies into 'high' and 'low' types, the 'low' types including all those in which there is a visible external fistula, and the 'high' those in which the lesion is believed to lie above the levator ani which forms the muscular sheet of the pelvic floor. In fact only covered anus and anorectal stenosis are 'low' lesions in the sense that the abnormality lies below the levator ani. All the others are 'high' lesions in the sense that the rectum ends blindly above the levator ani muscular diaphragm, though it may communicate with the exterior by a fistulawhich passes between the limbs of the puborectalis sling ofthe levator ani to the urethra, the posterior fornix or lower end of the vagina, or to the perineum. The passage of meconium through such a fistula may be another source of confusion, since even when the perineum is carefully