title: Characterisation of deep arterio-venous anastomoses within monochorionic placentae by vascular casting.
abstract: OBJECTIVE
  To characterise arterio-venous anastomoses (AVA) in monochorionic (MC) placentae and determine (i) whether shared cotyledons lie beneath the co-termination of an artery from one twin and a vein to the contralateral twin and (ii) whether all AVA can be detected by visual inspection of the chorionic plate.
  
  
  METHODS
  Vascular casts were made of 15 MC placentae. The number of typical AVAs suspected visually before digestion was compared with the number of AVAs identified after acid digestion.
  
  
  RESULTS
  Thirty-three of 67 (49%) suspected typical AVAs were confirmed as typical after casting. There were five false positives and no false negatives. The remainder were classified as atypical AVAs, found in > or =90% of MC placentae. Type I (small vascular connections between two apparently normal cotyledons not seen before casting) and Type II (shared cotyledons arising within larger apparently normal cotyledons) atypical AVAs were found in 53% and 73% of placentae, respectively.
  
  
  CONCLUSIONS
  Only half the shared cotyledons in MC placentae are characterised by co-termination of an artery and vein on the chorionic plate. We report the existence of deep anastomoses beneath the chorionic plate that cannot be visualised by chorionic plate inspection. These findings have implications for laser treatment of twin-twin transfusion syndrome.
authors.affiliation: Centre for Fetal Care, Queen Charlotte's & Chelsea Hospital, United Kingdom. l.wee@ic.ac.uk
authors.forename: L Y
authors.initials: LY
authors.lastname: Wee
authors.forename: M
authors.initials: M
authors.lastname: Taylor
authors.forename: N
authors.initials: N
authors.lastname: Watkins
authors.forename: V
authors.initials: V
authors.lastname: Franke
authors.forename: K
authors.initials: K
authors.lastname: Parker
authors.forename: N M
authors.initials: NM
authors.lastname: Fisk
mesh_terms: D000328:Adult; D001163:Arteriovenous Anastomosis / Q000033:anatomy & histology*; D002823:Chorion; D016319:Corrosion Casting / Q000379:methods*; D005260:Female; D005330:Fetofetal Transfusion / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D010920:Placenta / Q000098:blood supply*; D011247:Pregnancy; D014430:Twins, Monozygotic