Hearing gain after myringoplasty in relation to the size of tympanic membrane perforation

Objectives: To assess hearing gain after successful myringoplasty in relation to the size of tympanic membrane perforation. Methods: This cross-sectional study was done in the department of otolaryngology and head neck surgery, BSMMU, Sahbag, Dhaka during the period of January 2009 to December 2010.A total of 60 patients were under went myringoplasty operation after taking detailed history, clinical examination and investigation. Preoperative and postoperative hearing assessment was done. Analysed data presented by various tables, graphics and figures. Results: In case of small size perforation preoperative mean bone conduction threshold was 7.66 dB, mean air conduction threshold was 34.14 dB and mean air bone gap was 26.48 dB. In case of medium size perforation preoperative mean bone conduction threshold was 9.61 dB, mean air conduction threshold was 44.48 dB. Mean air bone gap was 34.87 dB. In case of large size perforation preoperative mean bone conduction threshold was 13.12 dB, mean air conduction threshold was 59 dB, and mean air bone gap was 45.88 dB. Hearing loss increases with increasing size of perforation. Ahmed and Rahim (1979) showed in the study that hearing loss increases with increasing the size of the perforation which was relevant in the study. After myringoplasty post-operative mean air bone gap was 21.24 dB in small size, 21.74 dB in medium sized and 24 dB in large size. From the record improvement of mean air bone gap or hearing gain was 5.24 dB in small size perforation respectively. The different of air bone gap closure between small and medium size perforation was statistically significant by unpaired’ test Conclusion: Hearing gain after myringoplasty is better in large size perforation.


Introduction:
Chronic suppurative otitis media is a worldwide health problem .The incidence of the diseases is very high in Bangladesh because of lower socioeconomic condition, overcrowding, poor nutrition and lack of health education. 1 Among the two types of chronic suppurative otitis media, tubo tympanic variety is more common and always characterized by central perforation of tympanic membrane. 2 The perforation is associated with discharge and hearing loss. This hearing loss is a matter of serious concern globally particularly in children and young adults because of its long-term effects on communication, language development, educational process and achievements. Hearing disability in adults is a burden to the individual, family and enter society. There is a significant quantitative correlation between the sizes of perforation with hearing loss. Myringoplasty operation is such a procedure by which patient improves hearing status. In my study I have proved that hearing gain is better in large size of perforation of tympanic membrane after successful myringoplasty.
Myringoplasty is the term used to describe the surgical repair of the perforated tympanic membrane. Attempts to close perforation of tympanic membrane started date back to the 16 th century. The advent of operating microscope, higher antibiotics, advances in anaesthesia and use of graft materials have resulted in myringoplasty becomes today one of the more commonly perforated otolaryngologic ear procedures in adults and children.
The size of perforation was graded according to involved surface area of tympanic membrane. It was graded as small (less than 25%), medium (50%-75%) and large (more than 75%) perforation of pars tensa. 3 One of the outcomes of successful myringoplasty is hearing improvement. The audiometric results following myringoplasty showed that closure of large perforation resulted in greater hearing gain than small perforation. A significant reduction in air bone gap following myringoplasty and had improved hearing. 4 In study Black Jh showed that postoperative air bone gap was less than 20 dB in 77.9% of patient. 5 An audiological improvement was also seen in 70.6% of patient in another study. 6

Methods:
Total 60 patients who underwent myringoplasty were studied in the department of otolaryngology and head neck surgery, BSMMU. Shahbag, Dhaka with their descriptive history, clinical findings, pre and post-operative assessment during the period of January 2009 to December 2010.
The assessment of the patient was done on the basis of history, clinical examination (Tuning fork test), radiological test (X-ray mastoid Town's view), laboratory investigation and hearing function test (pure tone audiometry and impedance).
Majority of the patients were operated under general anaesthesia, and rests were operated under local anaesthesia. Most of the myringoplasty were done by post auricular approach. Rest of the patients were operated by transcanal approach depends on the condition of the external auditory canal and position of perforation. In all of the patients Temporalis fascia was used as graft material. Under lay technique was used in every case. In patients with bilateral ear diseases operation was performed in one ear at a time. Operations were performed by different surgeons.
Patients were followed up post operatively up to 3 months, two follow up in this period. First follow up at the end of 1 month. 2 nd follow up at the end of 3 rd month. Pure tone audiometry was done during 2 nd follow up. During follow up condition of the wound, external auditory canal and tympanic membrane was noted. Hearing gain after myringoplasty was assessed on the basis of pure tone audiometry by closure of air bone gap.         In case of small size perforation preoperative mean bone conduction threshold was 7.66 dB, mean air conduction threshold was 34.14 dB and mean air bone gap was 26.48 dB. In case of medium size perforation preoperative mean bone conduction threshold was 9.61 dB, mean air conduction threshold was 44.48 dB. Mean air bone gap was 34.87 dB. In case of large size perforation preoperative mean bone conduction threshold was 13.12 dB, mean air conduction threshold was 59 dB, and mean air bone gap was 45.88 dB.

Results:
From this record it is showed that hearing loss increases with increasing size of perforation. Farrior and Lee 10,11 showed in the study that hearing loss increases with increasing the size of the perforation which was relevant in the study. After myringoplasty post-operative mean air bone gap was 21.24 dB in small size, 21.74 dB in medium sized and 24 dB in large size.
From the record improvement of mean air bone gap or hearing gain was 5.24 dB in small size perforation respectively. The difference of air bone gap closure between small and medium size perforation was statistically significant by unpaired' test (p=0.001). The different of air bone gap closure between medium and large size perforation was statistically significant by unpaired' test (p=0.001). The differennce of air bone gap closure between small and large size perforation was statistically significant by unpaired' test (p=0.000). Closure of large perforation resulted in greater hearing gain post operatively. 12 This is relevant with this Study.

Conclusion:
From this study, it can be concluded that size of tympanic membrane perforation affects the degree of hearing loss and improvement of hearing after myringoplasty. In relation to the size of perforation from the record, hearing gain was minimum in small size, medium in medium size and maximum in large size perforation. So, it was proved that hearing gain is better in large size of perforation after successful myringoplasty.