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As first described in 1950 by Raymond Carhart, the audiometric profile of classic otosclerosis presumes a "Carhart Notch" (CN) most likely to be found at 2000 Hz. Since that time, there have been multiple reports in the literature reporting CNs likely to be distributed between 500 and 2000 Hz. Perez et al (2009) revisited the issue in a retrospective analysis. They reviewed the records of 122 patients with a mean age 45 years, including 57 men and 65 women; 98 of whom (80 percent) had a CN in their pre-operative audiogram.
The distribution of CN's varied: 31 percent were found at 500 Hz, 32 percent were at 1000 Hz, and 37 percent were determined to be at 2000 Hz. Although the exact mechanism of the CN is not clearly known, the authors indicate it may be a mechanically induced effect. They speculate lower tone (500 Hz) CNs may suggest incus or malleus fixation, rather than traditional stapedial fixation.
For More Information, References, and Recommendations
Perez R, de Almeida J, Nedzelski JM, Chen JM. (2009) Variations in the "Carhart Notch" and Overclosure After Laser-Assisted Stapedotomy in Otosclerosis. Otology & Neurotology. 30(8):1033-1036.