Abstract
The region anterior to the anal canal in women is composed of intertwined smooth and skeletal muscles. The present study aimed to clarify skeletal muscle morphology in the anterior region of the anal canal. The pelvic floor muscles of 28 pelvic halves from 16 female cadavers (mean age 79.75 years) were dissected from the inferior aspect to examine the perineal muscles, followed by midline transection and dissection from the inner surface to examine the pelvic outlet muscles. The bulbospongiosus muscle was found to be attached to the lateral surface of the external anal sphincter. The superficial transverse perineal muscle crossed superiorly to the bulbospongiosus and coursed medially toward its contralateral muscle bundle deep to the anterior portion of the external anal sphincter. The superficial transverse perineal muscle formed the middle sling. From the medial aspect, the anterior part of the levator ani was divided into anterior and posterior bundles to form the anterior and posterior slings, respectively. This study proposes that three muscular slings could be important in supporting the pelvic floor in women. In addition, this study shows that the anterior skeletal muscular wall of the anal canal is composed of the anterior muscle bundle of the levator ani, superficial transverse perineal, and proper external anal sphincter muscles.
Highlights
The normal complex anatomy of the pelvic floor in women has been discussed extensively, especially with reference to the perineal body (DeLancey 1999; Petros 2001; Shafik et al 2007; Soga et al 2007; Abendstein et al 2008; Stein and DeLancey 2008; Larson et al 2010; Santoro et al 2015)
The longitudinal and circular layers of the smooth muscle are believed to be in the anorectal anterior wall, and the perineal body is described as a fibromuscular mass located between the anorectal canal and the vagina (Woodman and Graney 2002; Wu et al 2015; Plochocki et al 2016)
Previous studies investigating the positional relationships among the bulbospongiosus muscle (BS), the superficial transverse perineal muscle (STP), and the external anal sphincter (EAS) reported that these three muscles were continuous anatomically (Plochocki et al 2016), and demonstrated the relationships among the pelvic outlet muscles in three-dimensional (3D) topography (Larson et al 2010; Wu et al 2015)
Summary
The normal complex anatomy of the pelvic floor in women has been discussed extensively, especially with reference to the perineal body (DeLancey 1999; Petros 2001; Shafik et al 2007; Soga et al 2007; Abendstein et al 2008; Stein and DeLancey 2008; Larson et al 2010; Santoro et al 2015). The longitudinal and circular layers of the smooth muscle are believed to be in the anorectal anterior wall, and the perineal body is described as a fibromuscular mass located between the anorectal canal and the vagina (Woodman and Graney 2002; Wu et al 2015; Plochocki et al 2016). Previous studies investigating the positional relationships among the bulbospongiosus muscle (BS), the superficial transverse perineal muscle (STP), and the external anal sphincter (EAS) reported that these three muscles were continuous anatomically (Plochocki et al 2016), and demonstrated the relationships among the pelvic outlet muscles in three-dimensional (3D) topography (Larson et al 2010; Wu et al 2015). The positional relationships between the STP and the EAS remain unclear and controversial
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