Effects of adenoid hypertrophy on nasopharyngeal airway ventilation: A computational fluid dynamics study

Adenoid hypertrophy causes impaired nasopharyngeal airways (NA) ventilation. However, it is difficult to evaluate the ventilatory conditions of NA. Therefore, this study aimed to analyze the nasopharyngeal airway resistance (NA_RES) based on computational fluid dynamics simulations and the nasopharyngeal airway depth (NA_D) and adenoid hypertrophy grade measured on cephalometric cone-beam computed tomography images and determine the relationship between NA_D and grade and NA_RES to ultimately assess using cephalometric measurements whether NA has airway obstruction defects.

Cephalogram images were generated from cone-beam computed tomography data of 102 children (41 boys; mean age: 9.14 ± 1.43 years) who received orthodontic examinations at an orthodontic clinic from September 2012 to March 2023, and NA_D and adenoid grade and NA_RES values were measured based on computational fluid dynamics analyses using a 3D NA model. Nonlinear regression analyses were used to evaluate the relationship between NA_RES and NA_D and correlation coefficients to evaluate the relationship between grade and NA_RES.

NA_RES was inversely proportional to the cube of NA_D (R² = 0.786, P < 0.001), indicating a significant relationship between these variables. The resistance NA_RES increased substantially when the distance NA_D was less than 5 mm. However, adenoid Grade 4 (75 % hypertrophy) was widely distributed.

These study findings demonstrate that the ventilatory conditions of NA can be determined based on a simple evaluation of cephalogram images. An NA_D of less than 5 mm on cephalometric images results in NA obstruction with substantially increased airflow resistance.