ObjectiveTo investigate the differences in middle ear function between adenoid hypertrophy (AH) children with type A tympanogram and normal children, and to evaluate the value of wideband acoustic immittance (WAI) in diagnosing middle ear dysfunction in AH children with type A tympanogram. MethodsThis retrospective cohort study included 96 children (192 ears) with AH and 40 healthy children (80 ears) as the control group. All children underwent pure tone audiometry, 226 Hz tympanometry, WAI, otoscopy, and electronic nasopharyngoscopy. Type A AH children were selected as the study group (AH group) to compare the 226 Hz tympanometry index and WAI between the two groups. A binary logistic regression model was constructed after dimensionality reduction by principal component analysis of the frequencies with statistical significance, and the diagnostic value of the model was evaluated by receiver operating characteristic (ROC) curve. ResultsThere was no significant difference in 226 Hz tympanometry between the two groups (P>0.05). This study found that there were significant differences in WAI between children with AH and healthy children. Under tympanic peak pressure, the wideband absorbance (WBA) of the AH group was significantly higher than that of the control group at 226～630 Hz and 3 150～6 000 Hz; Under ambient pressure, the WBA of the AH group was significantly lower than that of the control group at 1 250～1 600 Hz and significantly higher than that of the control group at 4 000～6 000 Hz. The dimensionality of 15 statistically significant frequencies was reduced to 3 principal components (89.79% of the original information) by principal component analysis. The binary logistic regression model constructed after dimensionality reduction by principal component analysis had a high diagnostic value, with an AUC of 0.813, a sensitivity of 62.18%, and a specificity of 87.50%. ConclusionWAI can be used as an effective method for evaluating the middle ear function of AH children with type A tympanogram.