Variations in the "Carhart Notch" and Overclosure After Laser-Assisted Stapedotomy in Otosclerosis

Objective: The hallmark of bone conduction audiometry in otosclerosis is the "Carhart notch". The mechanism for this phenomenon is still not clearly understood. The objective of this study was to describe the pattern of bone-conduction threshold responses preoperatively in patients with otosclerosis and to assess overclosure after laser-assisted stapedotomy. Study Design: Retrospective case review. Setting: Tertiary academic referral center. Patients: One hundred twenty-two consecutive patients with sufficient audiometric follow-up who underwent CO2 laser-assisted stapedotomy were included. Their mean age was 45 T 12 years; 57 were men, and 65 were women. Intervention: Laser-assisted stapedotomy and analysis of preoperative and postoperative audiograms. Main Outcome Measure: Presurgical and postsurgical bone and air conduction audiograms. Results: Ninety-eight (80%) of 122 patients had a notch configuration in their preoperative audiogram. The notches were distributed as follows: 31% at 0.5 kHz, 32% at 1 kHz, and 37% at 2 kHz. A higher percentage of 0.5-kHz notches were observed in the group of 15 patients who did not achieve full air-bone gap closure. Eighty-one percent of the patients demonstrated overclosure in one or more of the frequencies between 0.5 and 4 kHz, which was maximal at 1 and 2 kHz ( mean, 7.5 and 8.3 dB, respectively). Conclusion: It seems that the morphology of the Carhart notch is variable and is not exclusively at 2 kHz as originally described. In addition, the increased prevalence of 0.5-kHz notches in individuals with a persistent air-bone gap may be indicative of other middle ear pathology such as incus or malleus fixation.