title: Morphology of the region anterior to the anal canal in males: visualization of the anterior bundle of the longitudinal muscle by transanal ultrasonography.
abstract: OBJECTIVE
  The anterior bundle of the longitudinal muscle in the region anterior to the anal canal in males has been described, although the anatomical details remain unclear. The present study was undertaken to clarify the precise morphology of the anterior bundle of the longitudinal muscle and its relationship to the surrounding structures, and to visualize the anterior bundle of the longitudinal muscle via transanal ultrasonography.
  
  
  METHODS
  Histological examination was carried out using seven male cadavers; an additional three male cadavers were used for transanal ultrasonography, and the ultrasonography images were compared with the actual sagittal sections. In addition, transanal ultrasonography images of 50 male patients at Tokatsu-Tsujinaka Hospital were studied.
  
  
  RESULTS
  The region anterior to the anal canal consisted of smooth muscles and skeletal muscles. The anterior bundle of the longitudinal muscle was situated between the bulbospongiosus and the external anal sphincter, and consisted of smooth muscle. The bundle was identified in the transanal ultrasonography of cadavers by comparison with the actual sections. Transanal ultrasonography images of living bodies showed the anterior bundle of the longitudinal muscle as a hypoechoic layer of approximately 17.7 mm in length.
  
  
  CONCLUSIONS
  The detailed anatomical findings of the anterior bundle of the longitudinal muscle suggested "an alternate arrangement of smooth muscles and skeletal muscles" in the region anterior to the anal canal and facilitated the visualization of the anterior bundle of the longitudinal muscle in transanal ultrasonography.
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.|Tokatsu-Tsujinaka Hospital, Shimbashi, Tokyo, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Muro
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.
authors.forename: Hisayo
authors.initials: H
authors.lastname: Nasu
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.
authors.forename: Masayo
authors.initials: M
authors.lastname: Harada
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Yamaguchi
authors.affiliation: Department of Clinical Anatomy, Tokyo Medical and Dental University (TMDU), 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8510, Japan. akita.fana@tmd.ac.jp.
authors.forename: Keiichi
authors.identifier: http://orcid.org/0000-0002-2927-2937
authors.initials: K
authors.lastname: Akita
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D002102:Cadaver; D006652:Histological Techniques; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D009130:Muscle, Smooth / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D014463:Ultrasonography / Q000379:methods*
keywords: Anal canal; External anal sphincter; Longitudinal muscle; Perineal body; Rectourethralis muscle; Ultrasonography