Abstract
Introduction The effects of tympanic membrane perforations on middle ear sound transmission are
not well characterized, largely because ears with perforations typically have additional
pathological changes. It has been established that the larger the perforation, the
greater is the hearing loss (HL).
Aim This study aimed to correlate the location and size of tympanic membrane perforation
and middle ear air space volume with the magnitude of HL in patients with tubotympanic
or inactive mucosal type of chronic otitis media (COM).
Materials and Methods A prospective clinical study of patients with tympanic membrane perforations due
to COM and without any other ear disease and who attended the Otolaryngology services
at our institute between July 2010 and December 2011 was conducted. A total of 300
ears were evaluated by performing otoendoscopy, followed by photo documentation and
audiological investigations (pure-tone audiometry and tympanometry). Tympanic membrane
perforations were categorized based on their size and location, and the mean air-bone
(AB) gap between the various types of perforations was compared and statistically
analyzed with significance level of p < 0.05.
Results Out of 300 ears, maximum number of ears (n = 124, 41.3%) had large-sized perforations (> 30 mm2) that had a maximum mean AB gap of 26.43 dB, and minimum number of ears (n = 60, 20%) had small-sized perforations (0–9 mm2) that had minimum mean AB gap of 9.12 dB. The remaining were medium-sized perforations
that had mean AB gap of 16.13 dB. Depending on the location, maximum were central
perforations (n = 198, 66%) and minimum were anterosuperior (AS) perforations (n = 9, 3%). Based on the middle ear volume on tympanometry, maximum ears were of low-volume
group (n = 246, 92%) that had larger mean AB gap of 19.96 dB HL when compared with the high-volume
group (n = 24, 8%) with 11.80 dB HL. AB gap was maximum at lower frequencies and decreased
with increase in frequencies except at 4,000 Hz, that is, 56.9 dB HL at 250 Hz, 42.6
at 500 Hz, 41.5 at 1,000 Hz, 32.4 at 2,000 Hz, and 49.5 at 4,000 Hz.
Conclusion HL increases as the area of tympanic membrane perforation increases. There is an
inverse relationship between HL and middle ear air space volume. Comparing the small-sized
perforations at different sites with the middle ear volume being low, it was found
that posterosuperior (PS) perforations had 4 to 7 dB greater HL than AS and anteroinferior
(AI). However, the relationship was statistically insignificant. The phase cancellation
effect of round window causing greater HL in posteroinferior (PI) perforations does
not exist in small- and medium-sized perforations. HL is greater at lower frequencies
and less at higher frequencies.
Keywords
air-bone gap - chronic otitis media - various sites and sizes of perforation
