Congenital choanal atresia is a condition in which the nasal cavity fails to communicate with the nasopharynx. This condition almost always presents in neonates, with history of episodes of cyclical cyanosis and respiratory distress that worsens during feeding and is relieved by crying. Up to two-thirds of cases of choanal atresia are unilateral, and bilateral cases are commonly associated with other congenital anomalies. It is not uncommon for unilateral disease to present later in life, whereas bilateral disease is considered to be incompatible with life and is rarely seen in adults.
Choanal atresia has an incidence of 1 in 5000 to 1 in 8000 live births. Fifty percent of all patients with choanal atresia and up to 75% of patients with bilateral disease have other associated congenital anomalies. Most common syndromes associated include CHARGE syndrome, Crouzon syndrome, and craniosynostosis. The incidence of mixed atresia is more common than pure membranous and bony atresias.
Generally, 65% to 75% of patients with choanal atresia are unilateral, whereas the rest are bilateral. About 30% are pure bony, whereas 70% are mixed bony-membranous. The atretic plate is usually sited in front of the posterior end of the nasal septum. The anatomic deformities include a narrow nasal cavity, lateral bony obstruction by the lateral pterygoid plate, medial obstruction caused by thickening of the vomer, and membranous obstruction. Acquired posterior choanal atresia rarely occurs. It is usually caused by rhinopharyngeal injury e.g. after adenoidectomy; radiotherapy for nasopharyngeal carcinoma); tuberculosis or syphilis of epipharynx, or sometimes by unknown causes.
There have been several theories regarding the embryogenesis of choanal atresia, but it is generally thought to be secondary to persistence of either the nasobuccal membrane of Hochstetter or the buccopharyngeal membrane from the foregut. This membrane normally ruptures between the fifth and sixth weeks of gestation to produce choanae. Failure of this membrane to rupture causes atresia of choanae. Other theories are abnormal persistence of mesoderm causing adhesions in the region of the nasal-choana or misdirection of mesodermal cell migration secondary to local factors. In addition, a defect in the region of the nasal and palatal processes surrounding the naso buccal membrane probably plays a role, leading to the associated findings of an accentuated arch of the hard palate, a medial location of the lateral and posterior nasal walls, and thickening of the vomer.
Since a newborn child is an obligate nasal breather, respiratory distress occurs with patients with bilateral choanal atresia at or shortly after birth. They present with cyclic cyanosis relieved by crying. Airway obstruction during feeding but relieved by crying demonstrates that the oral airway is intact while the nasal airway is obstructed. The improved respiratory distress after crying may delay the diagnosis. Respiratory collapse may occur, and feeding difficulties may lead to failure to thrive. Most patients with bilateral choanal atresia are detected within the first month of life. However, it can be diagnosed in adults with long-term bilateral nasal obstruction and rhinorrhea.
Patients with unilateral choanal atresia rarely present with immediate or severe airway obstruction. They normally present within the first 18 months of life with feeding difficulties and nasal discharge, but may present with unilateral nasal obstruction and discharge in later life. Obstruction of the contralateral side from infection or adenoid enlargement may precipitate airway symptoms and prompt medical evaluation. On anterior rhinoscopy, the occluded nasal cavity is typically filled with thick, tenacious secretions.
Initial clinical evaluation includes introduction of catheter via the nostrils, methylene blue dye test, cotton wisp test, and laryngeal mirror test. The distance of encountered resistance can provide insights into the etiology of nasal obstruction. An obstruction at approximately 1-2 cm from the ala rim in neonates is most likely deflection of the nasal septum or inferior turbinate while 3-3.5 cm from the alar rim indicates obstruction at the level posterior choanae. Flexible nasal endoscopy in a patient with proper preparation, such as nasal decongestion and mucous suctioning, allows direct visualization of the point of obstruction in the nasal passage and confirms the presence of an atretic plate in the choana.
Definitive evaluation is achieved with a CT of sinuses utilizing 2-5 mm cuts in patients with proper nasal preparation. CT demonstrated choanal atresia in form of the thickening of the anterior portion of the pterygoid plates and the enlargement of the posterior portion of the vomer, with or without membranous involvement.
Besides delineating the nature and severity of choanal atresia, CT is also useful in differentiating other causes of nasal obstruction from choanal atresia. Differential diagnoses include pyriform aperture stenosis, nasolacrimal duct cysts, turbinate hypertrophy, septal dislocation and deviation, antrochoanal polyp, or nasal neoplasm.