Choanal atresia (Fig. 13.3) results from persistence of the primitive oronasal membrane that separates the nasal cavity from the oral cavity, either unilaterally or bilaterally. When choanal atresia is bilateral, it is symptomatic at birth. In the absence of symptoms, choanal atresia is suspected when the pediatrician is unable to pass a nasogastric tube. The atresia may be osseous, membranous, or osteomembranous and is best evaluated by CT. The most common finding on imaging is thickening of the vomer. It is important to obtain axial images of the nasal cavity in a plane parallel to the hard palate; if this is not done, the posterior choanae may appear artifactually narrowed. It is also important to suction secretions from the nasal cavity prior to imaging in order to be able to assess the cause of atresia accurately. The orbits and temporal bones should be evaluated for coexisting anomalies that may indicate the CHARGE association (coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities/deafness). Imaging features of the CHARGE association are discussed in the chapter on the temporal bone and skull base.

Piriform aperture stenosis (Fig. 13.4) arises from abnormal development of the medial nasal eminences which results in failure of formation of the primary palate. The piriform aperture of the nasal cavity is therefore stenotic and the palate is narrow. It may be recognized clinically by a complete inability to pass a nasal catheter. This abnormality may be associated with fusion of the central maxillary incisors, forming a single central or mega incisor. Midline abnormalities of the brain including corpus callosal agenesis and holoprosencephaly may coexist. The stenotic piriform aperture is best evaluated with CT; it is useful to obtain an MRI to evaluate for coexisting brain abnormalities.

These mucoceles (Fig. 13.5) result from obstruction of the nasolacrimal duct by an imperforate valve of Hasner, a membrane that guards the inferior opening of the nasolacrimal duct. Normally, perforation of the valve of Hasner occurs immediately after birth due to increase in pressure within the lacrimal system when the infant cries. If perforation does not occur, a mucocele results. The process may be bilateral, and when the mucoceles are large enough, they may encroach upon the nasal cavity to produce respiratory distress. The lacrimal sac may also be dilated, especially if the valve of Rosenmuller, a membrane that is normally present at the junction of the common lacrimal canaliculus and the sac, is also imperforate. These are best evaluated by unenhanced CT. The most important differential diagnoses for an intranasal mass in a neonate are encephaloceles, dermoids, teratomas, and hemangiomas. The characteristic low density of the mucocele and its location along the course of the nasolacrimal duct are usually diagnostic.

Box 13.2 summarizes the embryological mechanisms that underlie the four types of midline nasal anomalies (Figs. 13.6, 13.7, and 13.8) and their typical imaging features. Each of these may present as a sinus or as a midline mass. An encephalocele is likely when the mass increases in size with crying. A firm mass may be a nasal heterotopia or a dermoid. Nasal glial heterotopias (also called nasal gliomas) are nonneoplastic disorganized rests of brain tissue that present as firm midline nasal masses and are best investigated with a combination of CT and MRI. The most important determination is if there is communication with the cranial cavity. With larger encephaloceles, this is usually not problematic and the herniation of meninges, CSF, and brain tissue through the midline frontonasal defect is usually obvious on MRI. Intracranial extension may not be as obvious in the case of dermal sinuses, nasal gliomas, and dermoid/epidermoid cysts. The presence of a widened foramen cecum or of a bifid crista galli is indicative of intracranial extension.