The effect of childbirth on the anal sphincters demonstrated by anal endosonography and neurophysiological tests.

Abstract

Obstetric trauma is a major cause of faecal incontinence in women resulting in considerable social disability. Until recently the development of faecal incontinence has been attributed largely to damage to the pelvic nerves. However the advent of anal endosonography has added a new dimension to our understanding of the pathophysiology of faecal incontinence. In this thesis, gross dissection and histological studies of 19 anorectal specimens was performed to demonstrate the normal anatomy. Simultaneous dissection and sonography of the anorectum (14 in vivo and 12 in vitro studies) has clarified the normal sonographic anatomy of the anal sphincters. Anal endosonography was performed in 114 healthy volunteers to demonstrate gender differences in anal sphincter anatomy. A prospective study of 12 patients undergoing secondary sphincter repair and 15 patients undergoing lateral internal anal sphincterotomy has validated the appearance of sonographic sphincter defects. A new technique of demonstrating the anal sphincters at rest using vaginal endosonography has been demonstrated in 20 women. A prospective study of 202 pregnant women using anal endosonography and neurophysiological tests has demonstrated that 35% of primigravidae (13% symptomatic) and 44% of multigravidae (23% symptomatic) develop occult anal sphincter defects during vaginal delivery. Although pudendal nerve damage can be identified in 16% of women 6 weeks after delivery, in the majority this recovers with time. Forceps delivery was identified as the single independent variable associated with sphincter damage although damage was also sustained in the absence of instrumental delivery. In a separate study of 50 women who sustained a recognized third degree tear 47% were found to be symptomatic despite a primary sphincter repair. In 85% of these women persistent anal sphincter defects were identified sonographically. In a further study of 43 women who had an instrumental delivery (17 vacuum and 26 forceps) anal sphincter defects were identified in 81% (38% symptomatic) of women who were delivered by forceps compared to 12% (21% symptomatic) delivered by the vacuum extractor. One hundred and fifty doctors and midwives were interviewed to assess their knowledge and training in perineal anatomy and repair. There was a clear deficiency in knowledge and inconsistencies in classification of third degree tears were apparent highlighting the need for more focused training in perineal anatomy and repair.