title: 3D Topography of the Young Adult Anal Sphincter Complex Reconstructed from Undeformed Serial Anatomical Sections.
abstract: Pelvic-floor anatomy is usually studied by artifact-prone dissection or imaging, which requires prior anatomical knowledge. We used the serial-section approach to settle contentious issues and an interactive 3D-pdf to make the results widely accessible.
  
  
  
  3D reconstructions of undeformed thin serial anatomical sections of 4 females and 2 males (21-35y) of the Chinese Visible Human database.
  
  
  
  Based on tendinous septa and muscle-fiber orientation as segmentation guides, the anal-sphincter complex (ASC) comprised the subcutaneous external anal sphincter (EAS) and the U-shaped puborectal muscle, a part of the levator ani muscle (LAM). The anococcygeal ligament fixed the EAS to the coccygeal bone. The puborectal-muscle loops, which define the levator hiatus, passed around the anorectal junction and inserted anteriorly on the perineal body and pubic bone. The LAM had a common anterior attachment to the pubic bone, but separated posteriorly into puborectal and "pubovisceral" muscles. This pubovisceral muscle was bilayered: its internal layer attached to the conjoint longitudinal muscle of the rectum and the rectococcygeal fascia, while its outer, patchy layer reinforced the inner layer. ASC contraction makes the ano-rectal bend more acute and lifts the pelvic floor. Extensions of the rectal longitudinal smooth muscle to the coccygeal bone (rectococcygeal muscle), perineal body (rectoperineal muscle), and endopelvic fascia (conjoint longitudinal and pubovisceral muscles) formed a "diaphragm" at the inferior boundary of the mesorectum that suspended the anorectal junction. Its contraction should straighten the anorectal bend.
  
  
  
  The serial-section approach settled contentious topographic issues of the pelvic floor. We propose that the ASC is involved in continence and the rectal diaphragm in defecation.
authors: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands; Institute of Computing Medicine, Third Military Medical University, Chongqing, 400038, China.
authors: Yi
authors: Y
authors: Wu
authors: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors: Noshir F
authors: NF
authors: Dabhoiwala
authors: Department of Anatomy & Embryology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors: Jaco
authors: J
authors: Hagoort
authors: Institute of Computing Medicine, Third Military Medical University, Chongqing, 400038, China.
authors: Jin-Lu
authors: JL
authors: Shan
authors: Institute of Computing Medicine, Third Military Medical University, Chongqing, 400038, China.
authors: Li-Wen
authors: LW
authors: Tan
authors: Institute of Computing Medicine, Third Military Medical University, Chongqing, 400038, China.
authors: Bin-Ji
authors: BJ
authors: Fang
authors: Institute of Computing Medicine, Third Military Medical University, Chongqing, 400038, China.
authors: Shao-Xiang
authors: SX
authors: Zhang
authors: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors: Wouter H
authors: WH
authors: Lamers
mesh_terms: D001003:Anal Canal / Q000473:pathology* / Q000601:surgery*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009132:Muscles / Q000601:surgery; D010502:Perineum / Q000601:surgery; D019651:Plastic Surgery Procedures / Q000379:methods*; D012007:Rectum / Q000473:pathology; D055815:Young Adult