Could the presence of a Carhart notch predict the presence of glue at myringotomy?

Abstract

The Carhart notch is a dip in the bone conduction at 2000 Hz without a corresponding dip in the air conduction. The main objective of this study was to establish how reliable is the presence of the Carhart notch in a preoperative audiogram in predicting the presence of glue at myringotomy. A prospective study has been carried out in 50 children presenting with glue ear to find out the association between the Carhart notch and the presence of glue at myringotomy. Children were seen before the operation and an audiogram and tympanogram were carried out. Myringotomy was carried out in 95 ears and the presence or absence of glue was recorded. The significance of the air-bone gap and the type of tympanogram in predicting a middle ear effusion were also examined. The audiograms of 37 ears showed a Carhart notch; of these, 36 ears were noted to have glue ear. The correlation between the presence of a Carhart notch in the preoperative audiogram and the presence of glue at myringotomy was found to be significant (P < 0.001) (chi-square test). Using the decision rule that the presence of a Carhart notch predicts the presence of glue, the following operating characteristics were determined: correct, 83 ears (87.4%); false positive, one ear (1.1%); false negative, 11 ears (11.6%). The presence of a Carhart notch was found to be a strong predictor of the presence of glue at myringotomy.