The anatomy of the perineal membrane: its relationship to injury in childbirth and episiotomy.
BACKGROUND
Episiotomy during childbirth, intended to protect the anal sphincter, may fail to do so. Furthermore damage to the anal sphincter complex may occur without complete perineal tear. We hypothesise that these particular injuries may occur due to posterior displacement of the anus leading to distraction of the anal sphincter complex from an anterior attachment to the perineal membrane. However, the anatomical basis for this has not been well defined.


OBJECTIVE
To investigate the relationship between the anal sphincter and the perineal membrane.


METHODS
High-resolution MRI scans of a female cadaver perineum were performed. The imaging findings were correlated with the anatomical structure identified on dissection and histological examination.


RESULTS
The perineal membrane was easily identified on MR imaging. Fibres from the perineal membrane could be seen to attach to the anal sphincter complex at the apex of the perineal body This was confirmed on histological examination and was a deeper layer than that of the decussation of the superficial transverse perineal muscle with the superficial part of the external anal sphincter.


CONCLUSIONS
The upper ano-rectal canal and apex of the perineal body have demonstrable attachment to the free margin of the perineal membrane postero-lateral to the lower vagina. This attachment would resist posterior displacement of the anal canal.
Hudson
Christopher N
CN
Department of Obstetrics and Gynaecology, St Bartholomew's and Royal London School of Medicine and Dentistry of Queen Mary College, United Kingdom.
Sohaib
Syed A
SA
Shulver
Helen M
HM
Reznek
Rodney H
RH
D000368:Aged; D002102:Cadaver; D004210:Dissection; D004841:Episiotomy / Q000009:adverse effects* / Q000379:methods; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007743:Labor, Obstetric; D008279:Magnetic Resonance Imaging; D010298:Parity; D036801:Parturition; D010502:Perineum / Q000033:anatomy & histology* / Q000293:injuries* / Q000473:pathology; D011237:Predictive Value of Tests; D011247:Pregnancy; D018570:Risk Assessment