Correlating the site of tympanic membrane perforation with Hearing loss
Titus S Ibekwe, Onyekwere G Nwaorgu2 and Taiwo G Ijaduola
Abstract
Background: It is recognized that the size of tympanic membrane(TM) perforation is proportional to the magnitude of hearing loss, however, there is no clear consensus on the effect of the location (site) of the perforation on the hearing loss. Hence the study is set to investigate the relationship between the location of perforation on TM and hearing loss.
Methods: A cross-sectional prospective study of consecutive adult patients with perforated TM
conducted in the ENT clinic of University College Hospital Ibadan between January 1st 2005 and July 31st 2006. Instruments used for data collection/processing include questionnaires, video and micro-otoscopy, Pure tone audiometer, image J and SPSS packages.
Background: It is recognized that the size of tympanic membrane(TM) perforation is proportional to the magnitude of hearing loss, however, there is no clear consensus on the effect of the location (site) of the perforation on the hearing loss. Hence the study is set to investigate the relationship between the location of perforation on TM and hearing loss.
Methods: A cross-sectional prospective study of consecutive adult patients with perforated TM
conducted in the ENT clinic of University College Hospital Ibadan between January 1st 2005 and July 31st 2006. Instruments used for data collection/processing include questionnaires, video and micro-otoscopy, Pure tone audiometer, image J and SPSS packages.
Results: Sixty-two patients (22-males, 40-females), aged 1675 years (mean = 35.4 +/- 4) with 77 perforated ear drums were studied and 15(24.2%) had bilateral TM perforations, 21 (33.9%) right unilateral and 26(41.9%) left unilateral. The locations of the TM perforations were 60(77.9%) central, 6 (9.6%) antero-inferior, 4(5.2%) postero-inferior, 4(5.2%) antero-superior and 3(3.9%) postero-superior respectively with sizes ranging from 1.51%89.05%, and corresponding hearing levels 30 dB 80 dB (59% conductive and 41% mixed). Fifty-nine percent had pure conductive hearing loss and the rest mixed. Hearing losses (dBHL) increased with the size of perforations (P = 0.01, r = 0.05). Correlation of location of perforations with magnitude of hearing loss in acute TM perorations was (P = 0.244, r = 0.273) and for chronic perforations (p = 0.047 & r = 0.31).
Conclusion: The location of perforation on the tympanic membrane (TM) has no effect on the magnitude of hearing loss in acute TM perforations while it is significant in chronic ones.
Background
Apart from conduction of sound waves across the middle ear, the tympanic membrane, also sub-serves a protective function tothe middle ear cleft and round window niche. Intact tympanic membrane protects the middle ear cleft from infections and shields the round window from direct
sound waves which is referred to as 'round window baffle'. This shield is necessary to create a phase differential so that the sound wave does not impact on the oval and round windows simultaneously. This would dampen the flow of sound energy being transmitted in a unilateral direction from the oval window through the perilymph. It has been found that the effect of the enhanced ratio of the surface area of the tympanic membrane to that of the oval window increases the sound pressure by about 27 decibel (dB) whereas the lever action of ossicles contributes about 3 decibel (dB).
A perforation on the tympanic membrane reduces the surface area of the membrane available for sound pressure transmission and allows sound to pass directly into the middle ear. As a result, the pressure gradient between the 'inner' and 'outer' surfaces of the membrane virtually becomes insignificant. The effectiveness with which the tympanic membrane transmits motion to the ossicular chain is thus impaired along with the level of hearing. It has been established that the larger the perforation on the tympanic membrane, the greater the decibel loss in sound perception. A total absence of the tympanic membrane would lead to a loss in the transformer action of the middle ear. The location of the perforation is believed by some schools of thought to have a significant effect on the magnitude of hearing loss.
For instance, posterior quadrant perforations are believed to be worse than the anterior ones because of the direct exposure of the round window to sound waves and perforations at or near the site of tympanic membrane attachment to manubrium have more severe effects than those of comparable size at different sites. However, some workers believe that there is no significant effect associated with location of the perforation.This divergent opinion, informed undertaking the study, set to investigate the relationship between the location of perforation on TM and the magnitude of conductive hearing loss with a view to contributing to the body of knowledge on this subject.
DOWNLOAD COMPLETE PDF HERE
Conclusion: The location of perforation on the tympanic membrane (TM) has no effect on the magnitude of hearing loss in acute TM perforations while it is significant in chronic ones.
Background
Apart from conduction of sound waves across the middle ear, the tympanic membrane, also sub-serves a protective function tothe middle ear cleft and round window niche. Intact tympanic membrane protects the middle ear cleft from infections and shields the round window from direct
sound waves which is referred to as 'round window baffle'. This shield is necessary to create a phase differential so that the sound wave does not impact on the oval and round windows simultaneously. This would dampen the flow of sound energy being transmitted in a unilateral direction from the oval window through the perilymph. It has been found that the effect of the enhanced ratio of the surface area of the tympanic membrane to that of the oval window increases the sound pressure by about 27 decibel (dB) whereas the lever action of ossicles contributes about 3 decibel (dB).
A perforation on the tympanic membrane reduces the surface area of the membrane available for sound pressure transmission and allows sound to pass directly into the middle ear. As a result, the pressure gradient between the 'inner' and 'outer' surfaces of the membrane virtually becomes insignificant. The effectiveness with which the tympanic membrane transmits motion to the ossicular chain is thus impaired along with the level of hearing. It has been established that the larger the perforation on the tympanic membrane, the greater the decibel loss in sound perception. A total absence of the tympanic membrane would lead to a loss in the transformer action of the middle ear. The location of the perforation is believed by some schools of thought to have a significant effect on the magnitude of hearing loss.
For instance, posterior quadrant perforations are believed to be worse than the anterior ones because of the direct exposure of the round window to sound waves and perforations at or near the site of tympanic membrane attachment to manubrium have more severe effects than those of comparable size at different sites. However, some workers believe that there is no significant effect associated with location of the perforation.This divergent opinion, informed undertaking the study, set to investigate the relationship between the location of perforation on TM and the magnitude of conductive hearing loss with a view to contributing to the body of knowledge on this subject.
DOWNLOAD COMPLETE PDF HERE
0 comments
Post a Comment