title: Absorption of the Wolffian duct and duplicated ureter by the urogenital sinus: morphological study using human fetuses and embryos.
abstract: OBJECTIVE
  To describe the embryological origin of the duplicated ureter and to investigate whether the urogenital sinus absorbs not only the Wolffian duct (WD) but also the ureter.
  
  
  METHODS
  During studies using sections of human fetuses (45 specimens), we incidentally found a specific type of ureteric duplication (at ~7 weeks) in which two unilateral ureters joined at the vesico-ureteric junction, apparently representing a morphology arising at an intermediate stage between complete and partial ureteric duplication. The existing literature lacks any photographic representation of early development of the vesico-ureteric junction, and we therefore studied horizontal sections of 10 human embryos (at ~5-6 weeks' gestation) in which the ureter did not join the urogenital sinus (future bladder) but instead joined the WD (future vas deferens).
  
  
  RESULTS
  The sinus consistently showed a reversed Y-shape, the arms of which extended posteriorly to receive the WD. When absorption of the duct into the sinus wall reached the distal end of the ureter, the arm-like parts appeared to enlarge posteriorly for further involvement of the duct, with little or no incorporation of the ureter; therefore, the future trigone of the bladder might develop from these arm-like parts of the sinus posterior wall. Consequently, in the case of ureteric duplication included in the present study, it is considered that the ureters would probably have merged with the WD at closely adjacent sites.
  
  
  CONCLUSIONS
  The present study represents the first photographic illustration of the early development of the human vesico-ureteric junction.
authors.affiliation: Department of Anatomy, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Naito
authors.affiliation: Department of Urology, Kobe University Graduate School of Medicine, Kobe, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Hinata
authors.affiliation: Faculty of Medicine, Institute of Embryology, Universidad Complutense Madrid, Madrid, Spain.
authors.forename: Jose Francisco
authors.initials: JF
authors.lastname: Rodriguez-Vazquez
authors.affiliation: Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, Iwamizawa, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.affiliation: Department of Anatomy, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Aizawa
authors.affiliation: Department of Urology, Kobe University Graduate School of Medicine, Kobe, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Fujisawa
mesh_terms: D005837:Genitalia, Male / Q000196:embryology*; D006801:Humans; D008297:Male; D014513:Ureter / Q000196:embryology*; D014928:Wolffian Ducts / Q000196:embryology*
keywords: Wolffian duct; human embryo; ureteric duplication; urogenital sinus; vesico-ureteric junction