Choanal Atresia

MICHAEL E. DUNHAM, MD

aFall 1998

CHOANAL ATRESIA IS a congenital anomaly of the anterior skull base characterized by closure of one or both posterior nasal cavities. The condition occurs in 1 out of every 7,000 to 8,000 live births. Approximately 60% of reported cases are unilateral with a right-sided predominance.

Bilateral choanal atresia is commonly associated with other congenital anomalies. The CHARGE association (Coloboma, Heart defects, choanal Atresia, Retarded growth, Genitourinary abnormalities, and Ear anomalies) is present to varying extent in approximately 50% of bilateral cases. Bilateral choanal atresia has been reported in association with other craniofacial syndromes and skull-based defects including encephalocele. Most unilateral cases are isolated anomalies.

FIGURE 1. Developmental anatomy of the face and nasal cavities (5 to 10 weeks gestational age). A. Development of the face. B. Sagittal sections through the developing nasal cavity. C. Coronal sections through the developing choanae—normal sequence. D. Coronal sections through the developing choanae—choanal atresia.

Embryology

During the fifth gestational week (see Figure 1), the nasal pits form on the developing face. The nasal pits invaginate the surrounding mesenchyme to form the nasal sacs. The oronasal membrane separates the nasal sacs from the primitive oral cavity. The primitive nasal choanae communicate with the oral cavity when the oronasal membrane ruptures during the eighth gestational week. As the lateral palatal shelves fuse to form the secondary palate, the definitive choanae are located at the junction of the nasal cavities and the nasopharynx. During development of the membranous nasal cavities, neural crest cells migrate from the anterior skull base region into the facial processes. These cells proliferate to form the bony/cartilaginous skull base and nasal vaults. The nasal vaults and choanae are completely formed by the end of the tenth week. Ossification of the anterior skull base is not complete until after birth.

Current theories of choanal atresia embryogenesis cite either failed oronasal membrane rupture or abnormal migration of neural crest cells into the nasal vault.¹ Failure of oronasal membrane rupture offers a simple explanation of choanal closure. The mesodermal flow theory more adequately explains the bony configuration of the atretic posterior nasal vault and the associated skull base deformities.²

Diagnosis

Bilateral choanal atresia causes respiratory distress at birth. Most newborns with the condition require early intubation. Neonatologists suspect the diagnosis when they can not pass a 6 French catheter through the nasal cavities into the nasopharynx.

FIGURE 2. Transnasal endoscopic view of choanal atresia.

Unilateral lesions may go undiagnosed until the child presents with persistent unilateral nasal drainage. Parents often report elaborate rituals of pulling strands of mucus from their child's nose. Careful questioning reveals an unusual susceptibility to upper respiratory symptoms. A few children have signs of respiratory distress at birth or develop obstructive sleep apnea during infancy if the nonatretic side is not sufficiently patent. A simple test for unilateral choanal stenosis is to have the child attempt nose blowing with the opposite nostril occluded by external pressure. Failure to detect any air movement is suspicious for complete obstruction. The differential diagnosis includes nasal septal deformity, nasal foreign body and choanal polyp. Failure to pass a catheter through the occluded nostril can be misleading in the older child because there is enough space in the nasal cavity for the catheter to curl without passing into the nasopharynx. The otolaryngologist can visualize the choanal closure with a small, flexible scope passed through the nostril (see Figure 2).

FIGURE 3. Axial CT scan demonstrating unilateral choanal atresia.

The CT scan with 3 mm transverse sections is the preferred method to confirm a diagnosis of unilateral or bilateral choanal atresia (Figure 3). The composition (membranous or bony) and thickness of the atresia is assessed. The depth of the nasopharynx and any associated skull base anomalies are detected. From the CT scan it is generally determined that there is some bony contribution from vomer thickening and medial displacement of the medial pterygoid plate. This causes a cone-shaped configuration to the atresia instead of the "atretic plate" that is commonly described. This has important implications for the managing surgeon with regard to the skull base structures that lie directly behind the atresia and the ultimate orientation of the surgically reconstructed opening.

Management

Bilateral choanal atresia requires airway support immediately after birth. Oral intubation usually precedes the diagnosis. In cases associated with severe craniofacial anomalies, longer term airway support with a tracheotomy may be needed until definitive repair can be performed safely. In cases where the skull base has a relatively normal shape and there are no cardiac contraindications to general anesthesia, bilateral choanal atresia should be repaired shortly after birth.

Timing recommendations for repair of unilateral atresia vary in the literature. Repair at around 2 to 3 years of age is generally accepted. Nasal mucus drainage symptoms seem to become troublesome for parents, day-care attendants and the child at this time. The anatomy is sufficiently developed to facilitate easy access to the posterior choanae, and intraoperative blood transfusion is not normally required for repair at this age. If there is associated obstructive sleep apnea, failure to thrive or respiratory distress, early repair of a unilateral lesion may be indicated.

Surgical procedures to correct choanal atresia can be broadly classified into transnasal and transpalatal approaches. The decision to use a transnasal versus a transpalatal approach rests on the surgeon's assessment of the choanal anatomy.³ The composition of the atretic plate, the depth and shape of the nasopharynx, and the presence of other anomalies are the most important factors. The transnasal approach requires less operative time and causes slightly less morbidity related to the incision. The transpalatal approach provides better exposure and more accurate bone removal. The palatal incision increases operative time and blood loss. The transpalatal approach probably reduces the risk of major vascular injury, intracranial complications, and restenosis.

FIGURE 4. Intraoperative transpalatal exposure of the posterior choanae.

The transnasal procedure is best for thin membranous atresias in older children. It does not allow sufficient exposure for extensive bone removal. The thickened vomer and lateral pterygoid plates can not be approached effectively in patients with small nasal cavities. Because the surgeon is "blinded" to the posterior nasopharyngeal wall during transnasal choanal atresia repair, a shallow nasopharynx is a relative contraindication to this approach.

The transpalatal approach (Figure 4) is best for thick bony atresias, bilateral atresias in neonates, and in cases where there are anomalies affecting the anterior nasal cavities or nasopharynx. The surgeon exposes the nasopharynx through a U-shaped incision in the hard palate musosa.

FIGURE 5A. Transpalatal surgical repair of choanal atresia. Palatal mucosal flap elevation.

The mucosal flap is elevated to the posterior edge of the hard palate and the soft palate muscular layer is incised where it inserts into the posterior edge of the hard palate (Figure 5a).

FIGURE 5B. Transpalatal surgical repair of choanal atresia. Exposure of the posterior hard palate and opening of the atresia.

A drill is used to remove the bone along the posterior edge of the hard palate, vomer, and pterygoid region (Figure 5b). Nasal mucosal flaps are elevated and preserved. Stents are then positioned through the new choanal openings and secured with the anterior ends of the stent just within the nasal vestibule. Operative complications including bleeding, skull base injury, and orbital injury are rare with the transpalatal procedure.

Older children with unilateral atresias are discharged one or two days after surgery and resume normal activities one week later. Newborns undergoing bilateral repair require hospitalization and airway observation for 3 to 4 days after surgery. The parents learn nasal stent care, airway precautions, and basic cardiopulmonary resuscitation before discharge. Home bradycardia-apnea monitoring is continued until the child is 3 months old. The parents are instructed to use saline drops and sterile suction technique to keep the stents patent. The stents are suctioned with an 8 French suction catheter 2 to 3 times daily.

The nasal stents are usually removed under general anesthesia 6 to 10 weeks after repair. The choanae are inspected endoscopically to assess healing. Subsequent choanal dilation is scheduled depending on the child's nasal breathing and the endoscopic appearance of the choanae.

Re-stenosis is the most common long-term complication after choanal atresia repair. Surgery is successful in more than 90% of unilateral cases. Revision surgery for re-stenosis is necessary for 20 to 25% of patients undergoing bilateral choanal atresia repair.

REFERENCES

1. Heneger AS, Strom M: Choanal atresia: A new embryonic theory and its influence on surgical management. Laryngoscope 1982;92:913–921.

2. Dunham ME, Miller RP: Bilateral choanal atresia associated with malformation of the anterior skull base: Embryogenesis and clinical considerations. Ann Otol Rhinol Laryngol 1992;101:916–919.

3. Jacobs IN: Choanal atresia repair. Current Opinion in Otolaryngology and Head and Neck Surgery 1996;4:434–439.

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