<prompt> Choanal atresia is due to persistence of ?Bucconasal membraneOropharyngeal membraneLaryngo tracheal foldTracheoesophageal fold  <response>: Choanal atresia is an abnormality of canalization during development of the nasal passages. It involves bone andor soft tissue and may result in either paial choanal stenosis or complete obstruction of the posterior nasal airway. The most widely accepted mechanism for the development of choanal atresia is the persistence of the bucconasal membrane beyond the sixth week of gestation, but abnormal migration of cephalic neural crest cells following neural tube closure also has been implicated. The incidence of choanal atresia is 1 in 7000 to 8000 live bihs. It is more common in females 2:1, more likely to be bony or cailaginous than membranous 9:1, and more commonly unilateral and right-sided 2:1. 