title: MRI findings in multifetal pregnancies complicated by twin reversed arterial perfusion sequence (TRAP).
abstract: BACKGROUND
  Twin reversed arterial perfusion sequence (TRAP) is a rare complication in multifetal monochorionic pregnancies in which a normal "pump" twin provides circulation to an abnormal acardiac co-twin, resulting in high-output cardiac dysfunction in the pump twin.
  
  
  OBJECTIVE
  To define fetal MRI findings of TRAP sequence.
  
  
  METHODS
  Fetal MR images were retrospectively reviewed in 35 pregnancies complicated by TRAP sequence. Abnormalities of the pump twin, acardiac twin, umbilical cord, placenta and amniotic fluid were reviewed.
  
  
  RESULTS
  Acardiac twins were classified as: acephalus (51%), anceps (40%), amorphus (9%), acormus (0%). Common findings in acardiac twins include subcutaneous edema (77%), absent cardiac structures (86%), absent or abnormal thoracic cavity (100%), abnormal abdominal organs (100%), superior limbs absent (46%) or abnormal (51%), and inferior limbs present but abnormal (83%). There were pump twin findings of cardiac dysfunction in 43% and intracranial ischemic changes in 3%. Umbilical cord anomalies were present in 97%.
  
  
  CONCLUSIONS
  Acardiac twins present with a predictable pattern of malformation with poorly developed superior structures, more normally formed inferior structures and absent or rudimentary heart. Although usually absent, abnormal heart structures can be seen and do not exclude TRAP sequence. Pump twins are commonly normal with exception of findings of cardiac dysfunction and possible brain ischemia.
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., MLC 5031, Cincinnati, OH 45229-3039, USA. carolina.guimaraes@cchmc.org
authors.forename: Carolina V A
authors.initials: CV
authors.lastname: Guimaraes
authors.forename: Beth M
authors.initials: BM
authors.lastname: Kline-Fath
authors.forename: Leann E
authors.initials: LE
authors.lastname: Linam
authors.forename: Maria A Calvo
authors.initials: MA
authors.lastname: Garcia
authors.forename: Eva I
authors.initials: EI
authors.lastname: Rubio
authors.forename: Foong-Yen
authors.initials: FY
authors.lastname: Lim
mesh_terms: D005260:Female; D005330:Fetofetal Transfusion / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011296:Prenatal Diagnosis / Q000379:methods*; D014427:Twins