Hearing Evaluation after Myringoplasty in Underlay Technique

Objective: to determine the success rate of underlay technique of myringoplasty regarding rate of graft take, complications and hearing improvement. Methods: This Cross sectional study was done in the department of ENT & Head-Neck Surgery, Dhaka Medical College Hospital & Shaheed Suhrawardy Medical college Hospital, Dhaka from July 2012 to December 2012. Sixty(60) patients who underwent myringoplasties were included in the study. All myringoplasty were performed by a postaural approach using autologous temporalis fascia and underlay technique. Results: The total success rate (graft uptake) was 88.3% and of the successful cases an overall hearing improvement was achieved in 73.58% of cases. The mean audiological improvement in air conduction threshold was 13.24 dB & mean closure of the air bone gap was 11.64 dB. The mean values of hearing gain of small perforations and subtotal perforations have shown significant difference.The mean values of hearing gain between posterior perforation and subtotal perforation have shown significant difference. Conclusion: Underlay myringoplasty is an effective technique of repairing the tympanic membrane perforation due to high rate of graft take and marked hearing improvement.


Introduction
Tympanic membrane perforation primarily results from middle ear infections of acute or chronic onset, trauma or iatrogenic. In Bangladesh, chronic otitis media is very common. Patients with COM usually presents with recurrent ear discharge, deafness and Tympanic membrane perforation. The degree of hearing impairment depends on the size of the perforation and the state of the ossicular chain. A hole in the tympanic membrane reduces the effective area of the membrane in contact with the sound wave, the pressure differential across the Tympanic membrane, reduce the mechanical coupling between the remaining intact portion of the membrane & malleus 1 .
There is a significant quantitative correlation between the size and site of perforation & hearing loss. Small perforations (10% of the tympanic membrane) produce losses of 10-15 dB below 3 KHZ. Large perforations produce severe losses over the whole range particularly at higher frequencies through these perforations, the sound waves act directly on the round and oval windows. Moderate perforations (10-40% of the tympanic membrane) have far more severe effects when placed on the posterior & superior margin of the membrane than when placed on the anterior & inferior margin. However non marginal perforations with intact ossicular chain hearing loss is approximately 10-30 dB 2 . The literature suggests that upto 80% of these perforations undergo spontaneous closure 3 .
Myringoplasty is the term used to describe the surgical repair of a perforated tympanic membrane. The success rate remained low until wullstein & Zoellner introduced the operating microscope into otologic surgery in the 1950s 5 .
Myringoplasty has gone through many changes in techniques and grafting materials. The size of various perforation is lebeled in relation to their quadrants as small, medium and large. Further perforations in the tympanic membrane are described according to their anatomical location. Central perforations are in the pars tensa. The location of central perforation is denoted by their relationship to the handle of malleus & can be termed as anterior, posterior, inferior or subtotal.
Perforated tympanic membrane can be repaired by a variety of graft materials like autologous temporalis fascia, perichondrium, cartilage and adipose tissue and can be approached by endoaural, postaural or transcanal route. Graft can be placed by underlay, overlay and inlay (sandwich) technique. 6 Success rates for closure of tympanic membrane 60-90 percent in adult and 35-94 percent in children 7 . The closure rate is reported to be higher in smaller perforations (74%) than large perforations (56%) 8 . Palva and Ramsay looked at the outcome of 281 Myringoplasties in their department, the closure rate was 97% and mean hearing improvement was 8.0 dB 9 . There has been shown to be direct correlation between hearing gains following Myringoplasty and preoperative perforation size 8  Exclusion Criteria: Patients having atticoantral disease, ossicular chain abnormalities, COM with sensori neural deafness, inner ear abnormality,history of previous ear surgery, patient requiring any other procedure upon middle ear than Myringoplasty,mentally ill person.
Data were collected by detailed history, clinical examination, pure tone audiometry. All myringoplasty were performed by a postaural approach using autologous temporalis fascia and underlay technique. During follow-up examination every patient who underwent Myringoplasty in underlay technique were examined weekly interval for first month, then 5th & 9th weeks of postoperative period & after that as needed. Audiometric tests were performed before operation & on 5 th & 9 th weeks of postoperative period. All information were endorsed in the data sheet. Audiometric findings and result were expressed in table form.

Results
Overall graft taken in 53 out of 60 cases (88.3%) & graft failure in 7 cases (11.7%). Hearing gain occurred in 39 (73.58%) patients & no improvement seen in 14(22.42%). There is not a statistically significant difference between the younger and older age group regarding hearing improvement. Mean preoperative & postoperative air conduction threshold(9 th week) in successful cases was 43 dB & 29.76 dB respectively with a mean audiological improvement was 13.24 dB. Improvement of air bone gap was 11.64 dB. Hearing gain of small perforation and subtotal perforation and posterior perforation and subtotal perforation have showed significant difference.    were significantly greater than those observed in subtotal perforations(11.46 dB gain in ABG) Considering significant outcome of the study, it has been tried to overcome the limitations as far as possible. Beyond the scope, following limitations were encountered in the study.
1. This study is conducted among a small number of cases within a short time frame in few centers. The result of this study may not reflect the total scenario.
2. Reperforation of tympanic membrane may occur upto two years after myringoplasty. So long term follow up of the patients are recommended.

Conclusion
Underlay myringoplasty is an effective technique of repairing the tympanic membrane perforation due to high rate of graft take and marked hearing improvement. Factors influencing hearing improvement were size & site of perforation.