Predictive role of Carhart's notch in pre-operative assessment for middle-ear surgery.

OBJECTIVES: To evaluate the predictive role of the audiometric Carhart's notch for the assessment of middle-ear pathology prior to surgical intervention.

METHOD: In this retrospective analysis, a total of 315 operated ears of 305 patients were evaluated regarding their pre-operative pure tone audiograms and peri-operative findings. The probable relationship between the middle-ear pathologies found and the Carhart's notch found on pre-operative pure tone audiometry was investigated. Patients with conductive hearing loss who obtained at least a 10 dB improvement (at 1 and 2 kHz frequencies) in their bone conduction threshold post-operatively were included in the Carhart's notch group. The pathologies underlying Carhart's notch were compared.

RESULTS: Three hundred and fifteen ears of 305 consecutive patients with conductive hearing loss were operated on due to middle-ear pathology. In patients with otosclerosis and tympanosclerosis, a Carhart's notch was seen at 2 kHz in 28 (93 per cent) patients but at 1 kHz in only two (7 per cent). However, in patients with chronic otitis media, a Carhart's notch was seen at 1 kHz in 10 (55 per cent) patients and at 2 kHz in eight (45 per cent) patients.

CONCLUSIONS: Otitis media with effusion, tympanosclerosis and congenital malformations should be considered in the differential diagnosis of a patient with a Carhart's notch seen on pure tone audiometry. A Carhart's notch at 2 kHz indicates stapes footplate fixation, whereas one at 1 kHz indicates a mobile stapes footplate; the footplate mobility can thus be predicted pre-operatively.