Comparison of Pre and Post-operative Hearing Results in Canal Wall Down Mastoidectomy with Type III

Patients of ≥5 years age with the diagnosis of Chronic otitis media (squamous) with conductive or mixed hearing loss, needing canal wall down mastoidectomy and with intact and mobile stapes suprastructure at surgery who underwent classical type III tympanoplasty were included in the study. The pre and post-operative PTA was performed and evaluated. The post-operative hearing was assessed in terms of average ABG and size of ABG closure.


INtRODUCtION
Chronic otitis media (COM) is a chronic inflammatory disease of the middle ear and mastoid that often results in partial or total loss of the tympanic membrane (TM) and ossicles, leading to conductive hearing loss that can range in severity up to 60-70 dB. 1 COM is a common condition, affecting 0.5-30% of any community.Therefore, a conservative estimate of the number of people in the world suffering from COM is over 20 million. 2Among which the prevalence of squamous type of COM is 3.5% in Nepal. 3e goal of tympanoplasty is to restore sound pressure transformation at the oval window by coupling an intact tympanic membrane with a mobile stapes footplate via an intact or reconstructed ossicular chain and to provide sound protection for the round window membrane by a closed, air containing, mucosa lined middle ear. 4 The modern era of tympanoplasty was ushered in by Wullstein and Zollner.Wullstein classified the operations as types I through V.
The type III tympanoplasty is a well established technique for middle ear reconstruction when tympanic membrane, malleus and incus are missing or diseased, as is often seen in chronic otitis media (COM). 4In classical type III tympanoplasty or myringostapediopexy, disease is removed from tympanomastoid compartment and advancement of the tympanic membrane(TM) or placement of tissue graft is done on top of the stapes capitulum.The air-bone gap (ABG) range from 10-60 dB after this procedure.The Pure Tone Audiometry test performed within seven days prior to the operation by Hughson and Westlake method.The test was performed through Air Conduction and Bone Conduction mode.The Air Conduction threshold and the Bone Conduction threshold averages were calculated by taking the averages of 500, 1000, 2000 and 4000 Hz frequencies.The ABG was calculated by taking differences between Air conduction and Bone Conduction threshold.The Air and Bone conduction threshold was recorded both pre and post-operatively.The postoperative air bone gap (ABG) closure was calculated by taking the difference between the preoperative ABG and the postoperative ABG of the average frequencies of 500, 1000, 2000 and 4000 Hz.The audiometry results were reported according to American Academy of Otolaryngology-Head and Neck Surgery guidelines, except for thresholds at 3 kHz, which were substituted in all cases with thresholds at 4 kHz. 5r classical type III tympanoplasty, a temporalis fascia graft was used to bridge the middle ear air space and placed in contact with the stapes head.The graft was then draped over the facial ridge.

MAtERIAL AND MEtHODS
The follow up of patients were performed at or after 10 th week postoperatively.During follow up period, ears with minimal discharge from the mastoid cavity but with healed middle ear were subjected to pure tone audiometry (PTA) assessment.
The results were analyzed in terms of average postoperative ABG and ABG closure.P value was calculated using the independent samples test and P value of less than or equal to 0.05 was taken as significant.The data analysis was performed with the help of statistical software for social sciences (SPSS) version 11.5 for windows.

RESULtS
The total number of patients enrolled during the study period were 41 (53.2%) cases among these patients, 39 (95.1%) came for follow up and 2 (4.9%) patients were lost in the follow up.Among the cases from adequate follow up, 1 (2.4%) case was excluded from the study because of graft failure (Table 1).
The Post-operative ABG at frequencies 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz were found to be 37.9 dB, 30.1 dB, 22.0 dB and 29.2 dB respectively as compared to pre-operative ABG of 46.6 dB, 39.7 dB, 29.9 dB and 35.0 dB in these respective frequencies.These differences were statistically significant except at 4000 Hz.
The four frequency average pre-operative ABG which was 37.8 dB was reduced to 29.8 post-operatively with a net gain of 8.0 dB.This observed difference was found to be statistically highly significant with p value of <0.001.It was observed that the ABG was the smallest at 2000 Hz as compared with other frequencies in both pre and post-operative audiograms.

DISCUSSION
The objectives of this study were to compare the pre and post-operative hearing results in terms of average ABG and the size of ABG closure in patients undergoing CWD mastoidectomy with classical type III tympanoplasty using temporalis fascia.
In our study the average age of the patients in was 21.03, the range being 5 to 55 years.7][8][9] This variation may be attributed to the socio-cultural context that in our country older adults are a bit hesitant to undergo surgical treatment as compared to patients of younger age.We reported only short-term hearing results, because the long-term success of any ossicular repair is largely dependent on factors outside the control of the surgeon, i.e. patient follow-up rates; eustachian tube function; middle-ear stability; and the condition of the mucosa.The short-term results are hence a more accurate reflection of the actual reconstructive procedures.In each case, air-bone gaps were calculated using air conduction and bone-conduction thresholds at frequencies 500, 1000, 2000 and 4000 Hz.
Different methods have been used by different authors to report the pure tone audiometric post-operative hearing results in middle ear surgery in the literature.Among these ABG closure, the post operative ABG presented in 10 dB bins and air conduction threshold gain are commonly reported indicators of tympanoplasty outcome.We had applied average PTA-ABG and size of the ABG closure for audiological assessment.Air Bone gap of the average of four frequencies 500, 1000, 2000 and 4000 Hz were used for analysis.For calculation of the size of the post-operative PTA-ABG closure ABGs were divided into different bins of 0-5dB,0-10dB,0-20 dB, 0-30 dB, >30 dB.
In our study, the post-operative PTA-ABG showed statistically significant improvement as compared to pre operative PTA-ABG.Patients had average PTA-ABG of 37.8 dB pre-operatively and 29.8 dB post-operatively with a net gain of 8 dB.The difference between the pre and post-operative PTA-ABG results was statistically significant (P<.001).Our results are similar to the results of myringostapediopexy of Cheang et al. 10 In his patients (n=25) PTA-ABG pre-and post operatively were 28.25 dB and 24.7 dB.However our results are different from those of Dawes PJD. 7 He reports the average PTA-ABG using frequencies .5, 1, and 2 kHz of naturally formed myringostapediopexy (n=15) and myringostapediopexy formed after canal wall down mastoidectomy (n=35) to be 17.7 and 19.0 dB, the range being 5-41.7 and 6.7-38.4dB respectively.Depending upon a number of factors it is generally found that the success of myringostapediopexy is rather variable, the post operative PTA-ABG being anywhere between 10 and 60 dB. 1  Functional results are often influenced by wide variability in the surgical techniques employed, in the criteria used to evaluate hearing results and a number of other anatomical, physiological and pathological events that occur post-operatively in the middle ear as mentioned above.

CONCLUSION
The results demonstrate that mean pre and postoperative air bone gap were 37.8 dB and 29.8 dB respectively with a net gain of 8 dB.These differences were statistically significant.Similarly, the postoperative PTA-ABG ranged from 15-61.2 dB, suggesting the possibility of effect of multiple other factors.Therefore, when indicated CWD mastoidectomy with type III tympanoplasty can be performed for prevention of disease recurrence or progression without fear for impairing hearing.
A Prospective study performed in Ganesh Man Singh Memorial Academy of ENT and Head and Neck Studies, Tribhuvan University Teaching Hospital, Institute of Medicine, Maharajgunj, Kathmandu, Nepal from October 2006 to April 2008 and patients who were of ≥5 years, both gender, intact and mobile stapes suprastructure at CWD tympanomastoidectomy surgery for COM squamous type were included.

table 3 . the pre and post-operative PtA-AbG evaluation of patients with CWD mastoidectomy and classical type III tympanoplasty (n=38)
Shrestha et al.Comparison of Pre and Post-operative Hearing Rearing Results in Canal Wall...

table 1 . total distribution of patients (n=41)
Merchant et al report that type