Study Objectives: Obstructive sleep apnea (OSA) is a respiratory disorder caused by the obstruction of the upper airway during sleep. The most common cause of pediatric OSA is adenotonsillar hypertrophy. Adenotonsillectomy is the first-line treatment for pediatric OSA; however, OSA persists in a significant number of patients due, in part, to the method of evaluating enlarged adenoids and tonsil tissue. The reason for these effects on OSA severity is not clear. This study aimed to establish a method to diagnose the need for adenoidectomy or tonsillectomy. Methods: Twenty-seven Japanese children (mean age 6.6 years) participated in this study, undergoing polysomnography and computed tomography examination. Pharyngeal airway morphology (adenoids and tonsil tissue size, volume, and cross-sectional area [CSA]) and pressure on the upper airway were evaluated at each site using computational fluid dynamic analysis. Results: Apnea-hypopnea index (AHI) showed a strong linear association with maximum negative pressure (P max ) (AHI = −0.055* events/h P max −1.326, R 2 = .805). The relationship between minimum CSA (CSA min ) and P max was represented by an inversely proportional fitted curve (P max = −4797/CSA min −5.1, R 2 = .507). The relationship between CSA min and AHI was also represented by an inversely proportional fitted curve (AHI = 301.6 events/h/CSA min 1.22 , R 2 = .680). P max greatly increased if CSA min became ≤ 30 mm 2 . The negative pressure of each site increased when CSA measured ≤ 50 mm 2 . Conclusions: In children, when the CSA for each site is ≤ 50 mm 2 , AHI is likely to be elevated, and the patient may require tonsillectomy or adenoidectomy.

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