Congenital nasal pyriform aperture stenosis is a rare cause of nasal obstruction in the neonate. This condition is caused by a bony overgrowth of the median nasal process of the maxilla. An appropriate workup includes evaluation for associated anomalies and fine-cut CT. Surgical treatment is indicated in patients with respiratory difficulty or poor weight gain.
Congenital nasal pyriform aperture stenosis (CNPAS) is a rare cause of nasal obstruction in neonates. It is caused by a bony overgrowth of the medial nasal process of the maxilla. In their landmark article in 1989, Brown and colleagues first clinically described this condition. In their series of six patients, they suggested that this condition arose as an isolated anomaly. In 1992, Arlis and Ward described a series of six patients who had CNPAS, four of whom had evidence of associated anomalies. Since that time, approximately 30 cases have been described in the literature in the form of case reports and small case series. It is now clear that pyriform aperture stenosis can occur in isolation or can be associated with other anomalies. The true incidence of CNPAS is unknown, given the variable degrees of stenosis and clinical manifestations. When present, CNPAS is usually bilateral. CNPAS can easily be mistaken for choanal stenosis or even atresia, given the similar clinical presentation.
Anatomy and embryology
The normal development of the lip and palate occurs during the embryonic period, which is the first 12 weeks of intrauterine development. Specifically, nasal development begins at approximately 3 weeks of gestation. The nasal development begins with the formation of paired olfactory nasal placodes that develop into nasal pits. The nasal pits gradually deepen to separate the frontonasal process into medial and lateral nasal processes. The paired medial processes fuse in the midline at approximately 4 to 7 weeks of gestation to form the primary palate. This fusion also forms the premaxilla, philtrum of the upper lip, columella, and nasal tip. The lateral processes eventually fuse with the maxilla to form the pyriform aperture and lateral nasal wall. Secondary palate development begins after the primary palate is formed at approximately 8 weeks of gestation.
The pyriform aperture is a pear-shaped bony inlet bounded by the nasal bone superiorly, the nasal process of the maxilla laterally, and the horizontal process inferiorly. The pyriform aperture is the narrowest most anterior bony portion of the nasal airway. Any decrease in cross-sectional area leads to a significant increase in nasal airway resistance and associated nasal airway obstruction.
The developmental mechanism for formation of CNPAS remains unclear. Brown and colleagues hypothesized that at 4 months of gestation, an overgrowth of maxillary ossification at the nasal process of maxilla leads to CNPAS ( Fig. 1 ).
Evaluation
The differential diagnosis for nasal obstruction in the infant is limited and should include septal displacement, nasopharyngeal mass, pyriform aperture stenosis, choanal stenosis, and atresia. It is important to remember that infants are obligate nasal breathers until the age of approximately 4 months. In those patients in whom there is difficulty passing a catheter by way of the nose, choanal stenosis and pyriform aperture stenosis should be included in the differential diagnosis.
Patients who have CNPAS typically present with evidence of nasal airway obstruction with cyclic cyanosis relieved by crying, similar to patients who have bilateral posterior choanal atresia. Initial management centers on the establishment of an adequate airway, usually with an oral airway or McGovern nipple. In mild cases of obstruction with a stable airway and absence of feeding difficulties, conservative treatment is adequate. Conservative treatment consists of nasal humidification and decongestants with diligent follow-up. In severe cases, patients may require immediate intubation with ventilatory support. Ultimately, infants with severe nasal obstruction or congestion and difficulty in breathing have poor weight gain. These children are strong candidates for surgical intervention.
Although the diagnosis is often suggested by history and physical examination, radiographic confirmation should always be obtained. The radiographic imaging of choice is fine-cut CT with axial and coronal sections from the palate to the orbit. Intravenous contrast is usually not necessary. CT provides excellent bony detail, and therefore accurate analysis of the bony pyriform aperture and choanal anatomy. The finding of bony overgrowth of the nasal processes with resultant narrowing of nasal passages anteriorly confirms the diagnosis ( Fig. 2 ).
More recently, Lee and colleagues have described the use of three-dimensional (3D) CT for the evaluation of CNPAS. These researchers suggested that using 3D CT gives a more precise evaluation of the amount of nasal process of the maxilla to be ablated, and therefore aids surgeons in the preoperative treatment planning and postoperative evaluations.
Patients who have CNPAS in association with a single central maxillary incisor should be further evaluated, because there may be an association with holoprosencephaly (HPE) ( Fig. 3 ).
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