massive pericardial effusion in down syndrome with supravalvar pulmonary stenosis associated to left pulmonary collapse

background:  pericardial effusion (pe) in down syndrome (ds) patients  usually occur s   secondary to hypothyroidism,  but  we have   no  report of massive pericardial effusion in   euthyroid   down syndrome patient with  supravalvar  pulmonary stenosis . case presentation:  we  report ed   an   11-month-old  male with down syndrome   with  massive  pericardial  effusion that  had conservative management with levothyroxin   who presented w ith cyanosis , respiratory distress  and  dominantly  left  upper lobe  pulmonary collapse .   there was  no response to medical man agement by antibiotic therapy ,   o2 therapy with hood  and chest physiotherapy  after five day s .   pericardio c entesis  guided echocardiography  performed  o n the sixth day after admission and 1 8 0 cc transudated pericardial fluids  has  extracted . clinical  and para clinical  finding s   w ere   relieved   dramatically  12-2 4 hour after  p ericardiocentesis . however,  angiography showed  supravalvar pulmonary stenosis (sps ). conclusion:  we   assume that  the  chronic compression  effect of  massive  pericardial effusion  may be  a major  cause of  sps .