Choanal atresia is due to the persistence of
Choanal atresia 
Choana, also called posterior nares, is an opening in the posterior part of each nasal cavity, through which the nasal cavity communicates with nasopharynx.
Choanal atresia is a congenital anomaly characterized by closure of one or both posterior nasal cavies (i.e., choana). It is due to the persistence of bucconasal membrane.
Approximately 60- 70% of cases are unilateral and are more common on the right side.
Bilateral cases occur in 20-30% of patients and 50% of these patients are associated with other congenital anomaly, i.e.,
CHARGE syndrome
→ Coloboma, Heart defects, Choanal atresia, Retarded growth, Genitourinary abnormalies and Ear defects.
Diagnosis - Unilateral lesions go unnoticed until the child presents with persistent unilateral nasal discharge.
There is the absence of air bubbles in nasal discharge.
A simple test for unilateral choanal atresia is to have the child attempt nose blowing with opposite nostril occluded by external pressure.
Failure to detect any air movement is suspicious for complete obstruction.
Bilateral choanal atresia presents as respiratory distress in newborn and requires support immediately after birth.
Bucconasal membrane
Oropharyngeal membrane
Laryngotracheal fold
Tracheoesophageal fold