Choanal Stenosis and Atresia

Posterior choanal stenosis or atresia is the most common developmental narrowing of the nasal cavity, and is the most common cause of symptomatic neonatal nasal obstruction (Table 29-1). Choanal stenosis and atresia are due to failure of breakdown of the embryologic nasobuccal membrane at the level of the posterior choanae. In approximately 30% of cases, the narrowing or occlusion is purely bony. Most other patients have membranous occlusion in combination with bony narrowing. A pure membranous atresia is rare. Approximately 40% of children with choanal atresia have bilateral involvement. Choanal atresia occurs in approximately 1 in 5000 births.^1,2

In the neonate, bilateral choanal obstruction results in respiratory distress that is mitigated by crying (paradoxical cyanosis). Feeding difficulty is common because the infant cannot nurse and breathe at the same time. Because neonates are obligate nose breathers, immediate therapy is required in the presence of bilateral high-grade nasal airway obstruction. Unilateral choanal obstruction may not become clinically apparent until later in childhood. Potential symptoms of unilateral obstruction include nasal stuffiness, rhinorrhea, sleep apnea, and recurrent infection. In the young infant, passage of a nasal catheter of at least an 8 Fr diameter excludes the presence of clinically significant choanal obstruction.

The diagnostic imaging evaluation of choanal stenosis and atresia is best achieved with thin-section CT. Suctioning of the nasal cavity and the instillation of vasoconstrictive nasal drops prior to image acquisition improve the diagnostic quality of the examination. An air–fluid level is often present within the obstructed nasal cavity. The osseous alterations consist of medial deviation of the medial maxillary wall, lateral deviation and thickening of the vomer, and fusion or bridging of the vomer to the perpendicular plate of the palatine bone (Figures 29-1 and 29-2). By definition, abnormal narrowing is indicated by the demonstration of a posterior choanal width of less than 3.4 mm in a child younger than 2 years. A vomer width of more than 3.4 mm in a child less than 8 years of age is abnormal. Membranous obstruction occurs at the level of the junction of the perpendicular portion of the palatine bone with the pterygoid processes, anterior to the pterygoid plates.^3–5

Associated anomalies are present in about half of children with congenital posterior choanal atresia or stenosis, and are more frequent when there is bilateral disease. These anomalies include the CHARGE association (coloboma, heart defects, atresia of the choanae, retarded growth and development, genital anomalies, ear anomalies), Treacher Collins syndrome, and Pierre Robin syndrome.

Pyriform Aperture Stenosis

Narrowing of the nasal pyriform aperture can occur due to maldevelopment of the nasal process of the maxilla. This is a rare anomaly. The usual clinical manifestation is neonatal respiratory distress; the presentation can mimic that of choanal atresia. Infants with less severe involvement may present with feeding difficulties or episodes of cyclical cyanosis that are relieved by crying. Conservative therapy that includes decongestants is often sufficient for patients with mild pyriform aperture stenosis, whereas more severe forms usually require surgical correction.^6–8

Various other facial and intracranial anomalies have an association with pyriform aperture stenosis, including holoprosencephaly, pituitary abnormalities, and facial hemangiomas. Central midline incisor syndrome describes patients with a small nasal bridge, nasal pyriform aperture stenosis, and a single enlarged midline incisor. Other potential findings in patients with this syndrome include posterior pituitary ectopia, medial deviation of the cavernous portions of the carotid arteries, and Chiari I malformation.

CT imaging of pyriform aperture stenosis shows thickening and medial bowing of the nasal processes of the maxilla (Figure 29-3). Occasionally, there is a shelf of tissue that extends across the nostrils just inside the nares. The overall width of the nasal passage is narrow. A pyriform aperture width of less than 11 mm in a term infant is diagnostic. Abnormal dentition and a bony ridge along the underside of the palate (mid-palatal vomerine ridge) are confirmatory imaging findings. Imaging of children with central midline incisor syndrome shows a central megaincisor in addition to the manifestations of pyriform aperture stenosis. The hard palate is hypoplastic and has a triangular configuration. Careful examination of the pituitary gland with MR is indicated for these patients.^1,3,9

Arhinia

Arhinia, or congenital absence of the nose, is a rare anomaly. The anomaly can be unilateral or bilateral. There is lack of development of the nasal bones, nares, and nasal cavity. Ocular anomalies, maxillary hypoplasia, and occluded or absent nasolacrimal ducts are common in these children. Other potential associated anomalies include cleft palate, frontal cephalocele, frontal lobe gyral dysplasia, dysgenesis of the corpus callosum, microphthalmia, hypertelorism, and absence of the olfactory bulbs and tracts. Cross-sectional imaging studies serve to define the pathological anatomy and to assess for associated anomalies (Figure 29-4).^10,11

Developmental Abnormalities of the Nasal Septum and Turbinates

Developmental variations of the nasal septum include septal deviation, septal spur, and septal pneumatization. Substantial deviation of the septum occurs in approximately 20% of the general population. This deformity occasionally interferes with paranasal sinus function; for example, obstruction of the middle meatus due to lateral displacement of the middle turbinate. A septal spur can also interfere with drainage in the middle meatus. A large septal spur or a spur arising from a markedly deviated septum is a potential cause of facial pain, headache, or epistaxis (Figure 29-5). Expansion of the septum due to pneumatization occasionally is of sufficient severity to produce symptomatic interference with middle meatus drainage.¹²

Anomalies of the turbinates include pneumatization (concha bullosa) (see Figure 28-1), paradoxical turbinate, accessory turbinate, and duplicate turbinates. These developmental variations are usually of no clinical significance. Occasionally, turbinate anomalies lead to manifestations of nasal obstruction or paranasal sinus obstruction. Enlargement or deviation of a middle turbinate, such as with a prominent concha bullosa, can displace and narrow the ethmoid infundibula or interfere with drainage into the middle meatus.

Uncinate process anomalies are common. Some of these variations interfere with function of the ostiomeatal unit and thereby can lead to sinusitis. The most common variation is lateral deviation of the uncinate process and secondary narrowing of the semilunar hiatus. Coronal CT images of patients with this anomaly often have the appearance of fusion of the uncinate process tip to the floor of the ethmoid sinus or orbital wall (Figure 29-6). With true uncinate process tip fusion, however, there is lack of development of the ipsilateral maxillary sinus. Pneumatization of the uncinate process tip can cause obstruction of the infundibulum or semilunar hiatus.

Masses of the pediatric nasal cavity include various developmental and acquired lesions (Table 29-2). Most of these masses are nonneoplastic.

Nasolacrimal Mucocele

Congenital nasolacrimal mucocele (nasolacrimal duct cyst; endonasal dacryocystocele) is an endonasal cyst that is due to obstruction of the lacrimal duct at its insertion into the inferior meatus. The dilated lacrimal duct bulges into the nasal cavity. When large, the mucocele can cause clinical manifestations of nasal obstruction. This is the second most common cause of neonatal nasal obstruction, after choanal atresia. Bilateral lesions are present in about half of patients with nasolacrimal mucocele. Distal nasolacrimal duct obstruction, with or without mucocele formation, can lead to dilation of the lacrimal sac, that is, dacryocystocele or lacrimal sac mucocele. Imaging with CT or MR shows a nasolacrimal mucocele as a cystic mass in the inferior meatus on the nasal cavity (Figure 29-7). The inferior turbinate may be thinned and displaced. A dacryocystocele appears as a cystic medial orbital mass, just inferior to the medial canthus (Figures 29-8 and 29-9). Enlargement of the bony nasolacrimal canal is usually present in patients with congenital ductal obstruction (see Figure 27-11 in Chapter 27).¹³

Inflammatory Polyp

An inflammatory nasal polyp is a benign mass that arises from the mucosa. This is the most common etiology of a nasal cavity mass in children beyond infancy. Most occur in association with a chronic inflammatory process such as chronic sinusitis. Commonly associated conditions include cystic fibrosis, allergic rhinitis, asthma, and allergic fungal sinusitis. Coexistent paranasal sinus polyps are common. Imaging studies show 1 or more round or pedunculated soft tissue masses in the nasal cavity (Figure 29-10). On CT and MR, the attenuation values and signal intensities of the polyp are usually identical to those of sinonasal mucosa. However, polyps in patients with allergic fungal sinusitis often are hyperattenuating on unenhanced CT and hypointense on T2-weighted MR. (For additional discussion of sinonasal polyps, please see Chapter 28.)

Nasal Glioma

A nasal glioma is a mass of ectopic glial tissue at or near the root of the nose. The term glioma is a misnomer because this developmental lesion is not a neoplasm. The ectopic glial tissue is completely separate from the brain. The pathogenesis of this lesion is sequestration of glial tissue during closure of the normal transient anterior midline dural diverticula that are present during the embryonic phase of development (see Chapter 26). The mass consists of small islands of glial tissue within a matrix of fibrous tissue. Granulation tissue may also be present. Nasal glioma accounts for less than 5% of developmental nasal masses. Up to 15% of patients with nasal glioma have associated cerebral heterotopias. The differential diagnosis of a congenital midline nasal mass in an infant includes nasal glioma, dermoid/epidermoid, and cephalocele.^2,14–16

Nasal gliomas tend to grow slowly. Deformities of adjacent structures due to mass effect are common. The 3 forms of nasal glioma are extranasal, intranasal, and mixed. The extranasal type is most common, accounting for approximately 60% of cases. The location of an extranasal glioma is external to the nasal bones. The lesion is usually slightly offmidline at the bridge of the nose. An extranasal glioma can also occur adjacent to the inner canthus. The overlying skin is intact, although a capillary telangiectasia may be present. The lesion is firm to palpation and a reddish or bluish discoloration may be visible deep to the skin surface.

An intranasal glioma can occur as an isolated lesion (30%) or in combination with an extranasal component (10%). An intranasal glioma is located in the nasal cavity and/or nasopharynx; occasionally the mass protrudes through the nostril. The most common location is between the middle turbinate and the nasal septum. The nasal fossa is widened and the septum is deviated. A large lesion in an infant can lead to respiratory distress, particularly during feeding.

Cross-sectional imaging studies demonstrate a nasal glioma as a mass with characteristics of soft tissue. The margins of the lesion are well defined; invasion of adjacent structures does not occur. There is only minimal contrast enhancement. The lesion is isointense or hypointense relative to gray matter on T1-weighted MR images, and hyperintense on T2-weighted images. There is usually a heterogeneous appearance on T2-weighted MR sequences. Approximately 15% of nasal gliomas connect to the dura (Figure 29-11). In some instances, the connection consists of a fibrous stalk. Occasionally, there is an open communication with the subarachnoid space; in this situation, the lesion represents a form of encephalocele. As with nasal dermal sinuses, the foramen cecum may be enlarged in conjunction with a nasal glioma.^3,13,17