The Role of Occlusion of the External Ear Canal in Hearing Loss

Objective: The objectives are to determine and compare the degrees of hearing loss upon occlusion of the cartilaginous and the bony portion of the external ear canal (EAC).

Methods: There were 20 healthy participants with normal ears, and all gave an informed consent. After an otoscopy, a baseline pure tone audiogram (PTA) was conducted. If the PTA of the participant was normal, aqueous cream was applied with a syringe via an 18 G cannula, from the tympanic membrane up to the isthmus which corresponds to the bony ear canal. A second PTA was conducted, and subsequently the cream was removed via suction under microscope guidance. The procedure was then repeated with the cream applied from the isthmus to the aperture of the external ear canal using the same cannula followed by a PTA and removal of cream under microscope.

Results: The mean threshold difference of occlusion at both portions of the ear canal were compared and analyzed. The mean threshold difference of hearing loss upon occlusion at the cartilaginous EAC was 37.5 to 48 dB. The mean threshold difference of hearing loss upon occlusion at the bony EAC was less, with a range of 21 to 24.95dB. There was a statistical difference (p<0.05) in the hearing loss between the blockage of the cartilaginous canal versus the blockage of the bony canal with a maximum difference at 2kHz.

Conclusion: Cartilaginous block of the external ear canal causes more hearing loss than block of the bony ear canal. This correlates with the concept and properties of sound waves, resonance and impedance.