Objective assessment of posterior choanae and subglottis.

The assessment of children with suspected stenosis of the posterior choanae and the subglottis can be arbitrary and subjective. A study was therefore undertaken to assess the normal size of both posterior choanae and subglottis in normal children and ascertain their relationship. The size of the posterior choanae in 72 children ranged from 3-9.3 mm (3-5.5 mm when less than one year old, and 6.1-9.3 mm when older than one year). The two sides were of equal size in 51 children (p < 0.001), in 16 children the right side was larger than the left (p < 0.01), and in 5 children the left was larger than the right side. The subglottic size in 52 children ranged between 4.2-9.3 mm (1.2-5.5 mm when less than one year old, and 6.1-9.3 mm, when older than one year). The size of the subglottis was of equal size or within 1.0 mm of the average size of the two posterior choanae in 41 children (p < 0.001), and of different sizes in 11 children. Accurate and objective assessment of either area can therefore be made by measuring and comparing the two sizes in the same child.