title: Pathogenesis of acardiac twinning: clues from an almost acardiac twin.
abstract: OBJECTIVE
  To search for clues to the pathogenesis of acardiac twinning.
  
  
  METHODS
  We examined a case of monoamniotic twins in which twin A's only sonographic abnormality was a dilated, tortuous ductus venosus. Twin B also had this abnormality as well as multiple other anomalies that included enormous hydrops and a severely hypoplastic heart. Following termination of pregnancy, autopsy was performed.
  
  
  RESULTS
  Postmortem examination of the placenta confirmed monochorionic, monoamniotic placentation with two adjacent trivascular cords. Autopsy confirmed the sonographic findings of enormous hydrops in twin B with a severely malformed, almost nonexistent heart. In addition, the liver was small and was represented by a cyst-like structure with thin rims of congested parenchyma surrounding large vascular spaces.
  
  
  CONCLUSIONS
  We believe the sequence of events in this case was early twin-to-twin transfusion resulting in a dysfunctional heart in twin B. This enabled a twin reversal arterial perfusion sequence with further deterioration of twin B's heart and extreme congestion of deoxygenated blood exiting the heart into the inferior vena cava and ductus venosus. This case supports the concept that circulatory reversal in the face of an initially functioning heart may lead to congestion, tissue hypoxia and secondary organ atrophy.
authors.affiliation: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA. rdrigge@jhmi.edu
authors.forename: R W
authors.initials: RW
authors.lastname: Driggers
authors.forename: K J
authors.initials: KJ
authors.lastname: Blakemore
authors.forename: C
authors.initials: C
authors.lastname: Bird
authors.forename: K E
authors.initials: KE
authors.lastname: Ackerman
authors.forename: G M
authors.initials: GM
authors.lastname: Hutchins
mesh_terms: D000328:Adult; D004200:Diseases in Twins; D005260:Female; D005315:Fetal Diseases / Q000473:pathology; D005330:Fetofetal Transfusion / Q000150:complications; D005865:Gestational Age; D006330:Heart Defects, Congenital / Q000209:etiology / Q000473:pathology*; D006801:Humans; D015160:Hydrops Fetalis / Q000473:pathology; D008099:Liver / Q000002:abnormalities; D010920:Placenta / Q000473:pathology; D011247:Pregnancy; D016216:Ultrasonography, Prenatal