The author describes an adenoidal-nasopharyngeal ratio (AN ratio) obtained by simple linear measurements on lateral radiographs as a numerical expression of adenoidal size and of patency of the nasopharyngeal airway.
The adenoidal measurement“A”(Fig.1) represents the distance from A1, the point of maximal convexity along the inferior margin of the adenoidal shadow, to a line B, drawn along the straight portion of the anterior margin of the basiocciput. The distance“A”is measured along a line dropped perpendicularly from point A1 to its point of intersection with line B.
The nasopharyngeal space“N”(Fig.2) is measured as the distance between C1, the posteriorsuperior edge of the hard palate, and D1, the anteroinferior edge of the sphenobasioccipital synchondrosis.When the synchondrosis is not clearly visualized, point D1 is determined as the point of crossing of the postero-inferior margin of the lateral pterygoid plate (P) and the floor of the bony nasopharynx. The AN ratio is obtained by dividing the measurement for “A” by the value for“N”.
Based upon the statistical evaluation of 1, 398 infants and children between the ages of 1 month and 16 years (Table 1, Fig.3), the mean value for AN ratio increases for 0.33 at 1.5 months of age to 0.59 at 4 years 6 months of age, after which it decreases to 0.38 at 15 years 6 months of age. The AN ratio correlated well with visual estimation of adenoidal size made by experienced observers in 143 radiographs of 93 patients with adenoidal problems (Table 2, Fig.4).
The AN ratio is a valid means of assessing adenoidal size. AN ratio of 0.80 or greater represents enlargement of the adenoids in infants and children.