title: Fetal growth of the anal sinus and sphincters, especially in relation to anal anomalies.
abstract: OBJECTIVE
  The anal sinuses, small furrows above the pectinate line, sometimes form perianal abscesses in adults. We examined the pattern of fetal growth of the anal sinus and sphincters using 22 mid-term (8-18 weeks) and 6 late-stage (30-38 weeks) fetuses.
  
  
  RESULTS
  In mid-term fetuses, the external and internal sphincters gradually increased in thickness, depending on specimen size (from 0.2 to 1.5 mm), whereas the anteroposterior diameter of the anal canal at the epithelial junction was relatively stable (0.5-1.0 mm) irrespective of specimen size. Anal canal diameter increased less than twofold between mid-term and late-stage fetuses, from 0.5-1.0 to almost 2 mm, whereas sphincter thickness increased over tenfold, from 0.2-1.5 to almost 3.5 mm. The anal sinus often showed balloon-like enlargement when the sphincter muscle bundles were tightly packed in mid-term, but not in late-stage fetuses.
  
  
  CONCLUSIONS
  Large concentric mechanical stress from the sphincters in late-stage fetuses apparently prevented the anal sinus from expanding in a balloon-like manner. Conversely, to avoid anal stenosis, the growing sinuses maintained a luminal space of the anal canal in response to stress from rapidly growing sphincters. The inferiorly extending sinus usually provided temporal double canals separated by a thick column. In the presence of double lumens, anal canal duplication is likely to develop without any abnormalities of the anal epithelium and sphincters.
authors.affiliation: Fumon-in Clinic, Mashiko-cho, Tochigi, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Arakawa
authors.affiliation: Department of Surgery, Daejeon Sun Hospital, Daejeon, Republic of Korea.
authors.forename: Si Eun
authors.initials: SE
authors.lastname: Hwang
authors.affiliation: Department of Anatomy, Chonbuk National University Medical School, Geonji-ro 20, Deokjin-gu, Jeonju, 561-712, Republic of Korea. 407kk@hanmail.net.
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Anatomy, School of Medicine, Georg-August-Universität Gőtingen, Gőttingen, Germany.
authors.forename: Joerg
authors.initials: J
authors.lastname: Wilting
authors.affiliation: Department of Anatomy and Human Embryology, Institute of Embryology, Faculty of Medicine, Universidad Complutense, Madrid, Spain.
authors.forename: José Francisco
authors.initials: JF
authors.lastname: Rodríguez-Vázquez
authors.affiliation: Division of Internal Medicine, Iwamizawa Asuka Hospital, Iwamizawa, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.affiliation: Department of Surgery & Biomedical Research Institute, Chonbuk National University Hospital, Jeonju, Republic of Korea.
authors.forename: Hong Pil
authors.initials: HP
authors.lastname: Hwang
authors.affiliation: Department of Surgery & Biomedical Research Institute, Chonbuk National University Hospital, Jeonju, Republic of Korea.
authors.forename: Baik Hwan
authors.initials: BH
authors.lastname: Cho
mesh_terms: D001003:Anal Canal / Q000002:abnormalities* / Q000196:embryology* / Q000473:pathology; D018568:Crown-Rump Length; D047109:Fetal Development; D005333:Fetus / Q000002:abnormalities / Q000473:pathology; D006801:Humans
keywords: Anal canal duplication; Anal sinus; Anal sphincter; Anal stenosis; Anal transitional zone; Human fetus