Carhart's notch: a finding in otitis media with effusion

Abstract

Introduction: Carhart's notch (CN) is a false depression of bone conduction (BC) thresholds at 2–4 kHz initially described in cases of stapes fixation. This study was designed to estimate the incidence and assess the clinical significance of CN in cases of otitis media with effusion (OME) in children. Patients and methods: Clinical records of 50 patients of OME that showed CN were analysed, retrospectively. First 24 were identified as seen in outpatients and 26 were found out of 100 consecutive cases of OME. The criteria of CN were a minimum 10 dB depression in BC at any frequency 500–4000 Hz. Results: Fifty patients showed CN, with mean age of 8.8 years. All had myringotomies with or without insertion of grommets. The CN ranged from 10 to 20 dB in the majority and up to 30 dB in few cases. In 85 ears studied, the affected frequencies comprised of 2000 Hz in 80 (94%), 4000 Hz in 4 and 1000 Hz in one ear. Pre-operative tympanograms were of type B in 68 (80%), type C in 16 (18.8%) and type A in one ear. Middle ear fluid was thick glue in 57 (67%), serous in 5 (5.8%), and no fluid found in 23 (27%) cases. Oedematous, granular or polypoidal appearances of middle ear mucosa were noted in 57 (67%) of the ears. A normal mucosa was seen in 17 (20%), and no details were available in 11 (13%) ears. Post-operative audiograms showed improvements of BC thresholds in 72 (84.7%) of the ears. Conclusion: Our results show 26% incidence of CN in paediatric cases of OME, with evidence of thick fluid and abnormal middle ear mucosa in about two-thirds of cases. This suggests that CN may be of prognostic value for myringotomy outcomes. Statistically there is a significant correlation between presence of fluid on myringotomy and CN, and type of tympanogram and post-operative BC threshold improvement. There is no predictive value of CN in terms of character of the middle ear fluid. Studies with larger numbers may be required to determine this with more certainty. It can help clinically, however, in pre-operative assessment of these cases. It is our opinion that BC should be an essential part of routine audiometry in all cases of OME.