Choanal atresia: Blockage of the choana, the passageway from the back of one side of the nose to the throat. The choana is shaped like an inverted funnel which opens into the upper throat. There are two choanae. The choanae must be open to permit breathing through the nose. Choanal atresia can occur as an isolated birth defect in an otherwise normal baby or it may be part of a syndrome such as the CHARGE association. Surgery is needed to repair choanal atresia.