title: Anal canal anatomy showed by three-dimensional anorectal ultrasonography.
abstract: BACKGROUND
  Demonstrate precisely the anatomic configuration of the anal canal and the length and thickness of the anal sphincters using three-dimensional (3-D) anorectal ultra-sonography in both genders.
  
  
  METHODS
  Twelve normal volunteer males and 14 females, with a mean age of 52.4 and 50.3 years, respectively, were prospectively enrolled in this study. All individuals from both groups were submitted to anorectal ultra-sonography. The anal canal was analyzed, measuring the length and thickness of the external anal sphincter (EAE), internal anal sphincter (IAS), puborectalis muscle (PR) and the gap (distance from the anterior EAS to the anorectal junction) in the midline longitudinal (ML) and transverse (MT) planes, and the results were compared between quadrants and genders.
  
  
  RESULTS
  The distribution of sphincter muscles is asymmetric in both genders. The anterior upper anal canal is an extension of the rectal wall with all layers clearly identified. The anterior IAS is formed in the distal upper anal canal and is significantly shorter in female than in male in all quadrants. The anterior IAS length is shorter than the posterior and lateral in both genders. The anterior EAS length is significantly shorter (2.2 cm) and the gap is longer (1.2 cm) in female than in male (3.4 cm) (0.7 cm) (p < 0.05), respectively. The posterior and lateral EAS-PR is significant longer in males (3.6 cm) (3.9 cm) than in females (3.2 cm) (3.5 cm) (p < 0.05), respectively. The lateral EAS-PR is significant longer than the posterior part in both genders. The anterior IAS is significantly thicker in males (0.19 cm) than in females (0.12 cm) (p = 0.04).
  
  
  CONCLUSIONS
  3-D anal endosonography enabled measurement of the different anatomical structures of the anal canal and demonstrated its asymmetrical configuration. The shorter anterior EAS and IAS associated with a longer gap could justify the higher incidence of pelvic floor dysfunction in females, especially fecal incontinence and anorectocele with rectal intussusception.
authors.affiliation: Department of Surgery, Medical School of the Federal University of Ceara and Hospital Sao Carlos, Av Edilson Brasil Soares, 1892. Edson Queiroz, 60834-220, Fortaleza, Ceara, Brazil. sregadas@hospitalsaocarlos.com.br
authors.forename: F Sergio P
authors.initials: FS
authors.lastname: Regadas
authors.forename: Sthela M
authors.initials: SM
authors.lastname: Murad-Regadas
authors.forename: Doryane M R
authors.initials: DM
authors.lastname: Lima
authors.forename: Flavio R
authors.initials: FR
authors.lastname: Silva
authors.forename: Rosilma G L
authors.initials: RG
authors.lastname: Barreto
authors.forename: Marcellus H L P
authors.initials: MH
authors.lastname: Souza
authors.forename: F Sergio P
authors.initials: FS
authors.lastname: Regadas Filho
mesh_terms: D001003:Anal Canal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D019160:Endosonography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012727:Sex Characteristics