title: Nerve supply to the internal anal sphincter differs from that to the distal rectum: an immunohistochemical study of cadavers.
abstract: OBJECTIVE
  Fecal incontinence is a common problem after anal sphincter-preserving operations. The intersphincteric autonomic nerves supplying the internal anal sphincter (IAS) are formed by the union of: (1) nerve fibers from Auerbach's nerve plexus of the most distal part of the rectum and (2) the inferior rectal branches of the pelvic plexus (IRB-PX) running along the conjoint longitudinal muscle coat. The aim of the present study is to identify the detailed morphology of nerves to the IAS.
  
  
  METHODS
  The study comprised histological and immunohistochemical evaluations of paraffin-embedded sections from a large block of anal canal from the preserved 10 cadavers.
  
  
  RESULTS
  The IRB-PX came from the superior aspect of the levator ani and ran into the anal canal on the anterolateral side. These nerves contained both sympathetic and parasympathetic fibers, but the sympathetic content was much higher than in nerves from the distal rectum. All intramural ganglion cells in the distal rectum were neuronal nitric oxide synthase-positive and tyrosine hydroxylase-negative and were restricted to above the squamous-columnar epithelial junction. Parasympathetic nerves formed a lattice-like plexus in the circular smooth muscles of the distal rectum, whereas the IAS contained short, longitudinally running sympathetic and parasympathetic nerves, although sympathetic nerves were dominant.
  
  
  CONCLUSIONS
  The major autonomic nerve input to the IAS seemed not to originate from the distal rectum but from the IRB-PX. Injury to the IRB-PX during surgery seemed to result in loss of innervation to the major part of the IAS.
authors.affiliation: Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, 1007 Shimonagakubu, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan, y.kinugasa@scchr.jp.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kinugasa
authors.forename: Takashi
authors.initials: T
authors.lastname: Arakawa
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.forename: Mineko
authors.initials: M
authors.lastname: Fujimiya
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sugihara
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000294:innervation* / Q000601:surgery; D002102:Cadaver; D005242:Fecal Incontinence / Q000209:etiology; D005260:Female; D006801:Humans; D007001:Hypogastric Plexus / Q000033:anatomy & histology; D007150:Immunohistochemistry; D008297:Male; D009197:Myenteric Plexus / Q000033:anatomy & histology; D010275:Parasympathetic Nervous System / Q000033:anatomy & histology; D011183:Postoperative Complications / Q000209:etiology; D012007:Rectum / Q000294:innervation*; D013564:Sympathetic Nervous System / Q000033:anatomy & histology