The posterior choanae (funnel in Greek), also known as the posterior nasal apertures in English, are the holes that connect the nasal cavity with the nasopharynx. They are separated by the vomer (plowshare in Latin), the thin flat bone that forms the posteroinferior portion of the nasal septum.
Choanal atresia refers to the obstruction of one or both of these posterior choanae. This obstruction can be either bony or membranous. Because babies are obligate nose breathers, bilateral obstruction leads to severe respiratory distress. Unilateral choanal atresia, on the other hand, is ususally first diagnosed when the child is older.
The diagnosis can be made in the clinic by failure to pass a nasogastric tube. CT is needed, however, to differentiate membranous from bony atresia and to define the length of the obstruction, distinctions that determine the surgical management.
In bony choanal atresia, there is bony narrowing of the posterior choanae, < 3.4 mm (blue arrows); enlargement of the vomer (pink arrow); and inward bowing and thickening of the lateral walls of the nasal cavity (white arrows), which are apposed or fused to the vomer. These findings are not seen in membranous atresia.
A potential pitfall in estimating the thickness of the membranous atretic segment is the accumulation of secretions in the nose, which may give a falsely thick appearance of the atretic segment. CT, therefore, should be done after properly suctioning the nose and applying a topical vasoconstrictor.
nicely put, concise and to the point
ReplyDeleteDr, A. AbdelRahman, MD