A congenital abnormality that is characterized by a blocked CHOANAE, the opening between the nose and the NASOPHARYNX. Blockage can be unilateral or bilateral; bony or membranous.

Absence or abnormal closure of the choana (the posterior nasal aperture). Most embryologists believe that posterior choanal atresia results from a failure of rupture between the 35th and 38th day of fetal life of the partition which separates the bucconasal or buccopharyngeal membranes. The resultant choanal atresia may be unilateral or bilateral, bony or membranous, complete or incomplete. In over 90 per cent of cases the obstruction is bony, while in the remainder it is membranous. The bony type of atresia is commonly located 1-2 mm. anterior to the posterior edge of the hard palate, and the osseous septum varies in thickness from 1 to 10 mm. In the membranous form of choanal atresia the obstruction usually occurs further posteriorly. In approximately one third of cases the atresia is bilateral.

Choanal atresia (CA) is a congenital anomaly of the posterior nasal airway characterized by the obstruction of one (unilateral) or both (bilateral) choanal aperture(s), with clinical manifestations ranging from acute respiratory distress to chronic nasal obstruction.

Complete nasal obstruction in a newborn may cause death from asphyxia. During attempted inspiration, the tongue is pulled to the palate, and obstruction of the oral airway results.