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Auditory and vestibular disorders, Hearing sciences
Korean Journal of Audiology 2010;14(2):94-98.
Efficacy of a Long Silastic Sheet for Middle Ear Aeration during Surgery for Chronic Otitis Media
Jun Sung Kim, Hyun-Seok Choi, Hyong-Ho Cho
Department of Otolaryngology-Head Neck Surgery, Chonnam National University Medical School, Gwangju, Korea
Efficacy of a Long Silastic Sheet for Middle Ear Aeration during Surgery for Chronic Otitis Media
Jun Sung Kim, Hyun-Seok Choi, and Hyong-Ho Cho
Department of Otolaryngology-Head Neck Surgery, Chonnam National University Medical School, Gwangju, Korea
Abstract

Background and Objectives
To determine the effect of a long silastic sheet for middle ear aeration during surgery for chronic otitis media. 


Subjects and Methods
Between January 2003 and May 2007, 46 patients underwent a planned staged tympanoplasty and mastoidectomy, because of the possibility of residual cholesteatoma and severe swelling of the middle ear mucosa, especially around the stapes. A long silastic sheet was inserted from the mastoid cavity to the middle ear via the facial recess during the first stage of the operation. To determine the effect of the long Silastic sheet for recovery of mastoid aeration, various factors, such as computed tomography grading, Eustachian tube function grading, and hearing results, were compared. 


Results
During the average follow-up of 34.5 months, there was 1 recurrent chronic otitis media case, which was eventually revealed to be tuberculous otitis media. An intact tympanic membrane was obtained in 45 (97.8%) of 46 patients. In CT grading, middle ear aeration was increased significantly (p<0.05). The air-bone gap (ABG) was significantly decreased after the second stage of the operation [the pre-operative average ABG was 29.7 dB and the post-operative (last follow-up) average ABG was 21.0 dB; p<0.05]. Eustachian tube function did not influence middle ear aeration after the first stage of the operation. 


Conclusions
Long silastic sheet insertion from the mastoid to the middle ear is statistically effective for amelioration of middle ear and mastoid aeration after the first stage of the operation for chronic otitis media without other complications.

Keywords: Silicone;Middle ear ventilation;Otitits media;Tympanoplasty.

Address for correspondence : Hyong-Ho Cho, MD, Department of Otolaryngology-Head and Neck Surgery, Chonnam National University Medical School, Hak 1-dong, Dong-gu, Gwangju 501-190, Korea
Tel : +82-62-220-6772, Fax : +82-62-228-7743, E-mail : victocho@hanmail.net


Introduction

The goals in surgery for chronic otitis media (COM), including cholesteatomas, are to control the infection, maintain an intact tympanic membrane, hearing rehabilitation, and complete removal of the cholesteatoma. A planned staged tympanoplasty and mastoidectomy is recommended to accomplish these goals in cases with the possibility of a residual cholesteatoma and severe swelling of the tympanic cavity mucosa, especially around the stapes.1)
The degree of aeration in the middle ear and mastoid cavity after ear surgery is considered to be important for the postoperative results of reconstructive ear surgery.2) Pre-operative Eustachian tube (ET) function is known to affect the post-operative results of reconstructive ear surgery.3) 
For widening the route for mastoid ventilation, several surgical techniques, such as posterior tympanotomy and anterior tympanotomy have been developed.4,5) However, the relationship between those procedures and mastoid aeration recovery after surgery has not been verified. A silastic sheet was used to maintain the air space between the tympanic membrane and the middle ear mucosa, as well as to enhance middle ear mucosal regeneration.6,7) Use of a large silastic sheet in the middle ear and mastoid has been reported to be effective in restoring mastoid aeration and preventing recurrences of cholesteatomas.8)
In the present study, in order to determine the effect of a long silastic sheet for recovery of mastoid aeration, various factors, such as computed tomography grading, ET function grading using Valsalva and Politzer tests, and hearing results, were compared.

Subjects and Methods

Surgical procedure
Between January 2003 and May 2007, 46 patients with COM, including cholesteatomas, underwent a planned staged tympanomastoidectomy because of the possibility of a residual cholesteatoma and severe swelling of the middle ear mucosa. In all of the patients, during the first stage of the operation, diseased tympanic cavity pathology and mastoid cells were removed via a transcortical mastoidectomy and tympanoplasty. The aeration route between the middle ear and the mastoid cavity was re-established with a posterior tympanotomy (including incudal buttress removal) and by removing the malleus and the incus. A long silastic sheet (0.02 inches thick) was placed from the mastoid cavity to the ET orifice via the epitympanum and the facial recess to obtain an aeration route. In all of the cases, diseased mucosa and air cells in the mastoid cavity were totally removed by drilling and the posterior bony wall of the external auditory canal was preserved (Fig. 1). 
The second stage of the operation was performed more than 6 months after the first stage of the operation to remove the long silastic sheet and reconstruct the ossicular chain with Polycel
®.

Assessment of the efficacy of a silastic sheet for middle ear aeration
Temporal bone CT scanning was performed before the first stage of the operation and before the second stage of the operation. Aeration of the middle ear was evaluated using the following CT grading system for each patient: 
Grade 0, no air space in either the tympanic or mastoid cavity;
Grade 1, only mesotympanum aeration;
Grade 2, an air-filled mesotympanum and epitympanum, but no air space in the mastoid cavity;
Grade 3, an air-filled mesotympanum, epitympanum, and mastoid cavity (Fig. 2).3)
The results of recovery of aeration were assessed according to the pre-operative ET function and the types of COM.


Assessment of eustachian tube function
An ET function was evaluated by the Valsalva and Politzer tests (the Valsalva test involves patients holding their nose and blowing out with a closed mouth; for the Politzer test, one of the patient's nostrils is occluded with a rubber balloon as the examiner pinches the other nostril tightly, the patient elevates the palate by swallowing, and the examiner then forces air into the closed nasal cavity from the Politzer's bag). In combination with an otomicroscopic examination, both methods were performed before the first stage of the operation and before the second stage of the operation. The ET function was described using the the grading system for each patient: 
Grade 1, air connection was noted by the Valsalva test; 
Grade 2, air connection was not noted by the Valsalva test, but noted by the Politzer test; 
Grade 3, air connection was not noted by both tests.

Assessment of functional outcomes
We analyzed the hearing results with pure tone audiometry in patients who underwent a planned stage tympanomastoidectomy with a long silastic sheet insertion. Functional outcomes were evaluated by comparing air-bone gaps (ABG) before the first stage of the operation, before the second stage of the operation, and 3 months after the second stage of the operation. Audiometric analysis was performed according to the 1995 American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) guidelines, averaging the hearing threshold at four frequencies (500, 1,000, 2,000, and 3,000 Hz).

Statistical analysis
Statistical analysis was performed with an independent sample t-test, paired sample t-test, and χ2 test using SPSS, version 17.0 (SPSS Inc., Chicago, IL, USA), and a p<0.05 was considered to be significant. 

Results

Demographic data and anatomic results of otitis media surgery
Fourty-six patients (46 ears) underwent tympanomastoid surgery as treatment for COM (n=15), cholesteatomas (n= 20), adhesive otitis media (n=9), a cholesterol granuloma (n=1), and tuberculous otitis media (n=1). The patients (19 males and 27 females) ranged in age from 11-58 years, with an average of 37.9 years. The average follow-up was 34.5 months (range, 12-58 months) from the first stage of the operation and 20.2 months (range, 6-42 months) from the second stage of the operation. During the average follow-up of 34.5 months, there was 1 recurrent case with granulation tissue and otorrhea, which shown to be tuberculous otitis media. Intact tympanic membranes were obtained in 45 (97.8%) of 46 patients. After the first stage of the operation, there were no tympanic cavity adhesions, abnormal tympanic membrane healing, and infection except in one case. After the second stage of the operation, there was no prosthesis displacement. After antituberculosis medication in the case with tuberculous otitis media, the granulation tissue and otorrhea resolved.

Middle ear aeration change according to the types of COM
Middle ear aeration was assessed with temporal bone CT scans with axial and coronal sections. Each mesotympanum, epitympanum, and mastoid cavity was checked for the presence of aeration, and then aeration of the middle ear was evaluated using the CT grading system for each patient at each occasion. In CT grading, middle ear aeration was increased significantly (the average middle ear aeration was 0.60 before the first stage of the operation and 2.32 before the second stage of the operation; p<0.05; Fig. 3). The middle ear aeration in COM (n=15), attic cholesteatomas (n= 20) and adhesive otitis media (n=9) was significantly increased after the first stage of the operation (p<0.05), but in the cholesterol granuloma (n=1) and tuberculous otitis media (n=1) the middle ear aeration was not changed (Fig. 4).

Middle ear aeration change according to ET function 
ET function was not significantly changed after the first stage of the operation (the average ET function was 1.20 before the first stage of the operation and 1.13 before the second stage of the operation; p>0.05). The middle ear aeration grade was significantly increased (p<0.05) after the first stage of the operation, but was not influenced by ET function (p>0.05; Fig. 5).

Hearing results 
The average ABG before the first stage of the operation was 29.67 dB (average ABG in COM, 34.33 dB; cholesteatoma, 26.50 dB; adhesive otitis media, 30.56 dB), and the average ABG before the second stage of the operation was 36.63 dB (average ABG in COM, 41.67 dB; cholesteatoma, 34.00 dB; adhesive otitis media, 34.44 dB) which was significantly increased after the first stage of the operation (p< 0.05). The last follow-up ABG after the second stage of the operation with ossiculoplasty was 20.98 dB (average ABG in COM, 20.00 dB; cholesteatoma, 20.50 dB; adhesive otitis media, 21.67 dB) which was significantly improved from before the first and second stages of the operation (p<0.05; Fig. 6).

Discussion 

The major goals of middle ear surgery for chronic ear diseases are the eradication of the disease, preventing recurrence, and preservation of sound conductivity. To achieve these goals, the middle ear must be free from disease, the tympanic membrane must be intact, the middle ear space must be aerated and lined with mucosa, and the connection between the ear drum and the cochlea must be obtained.9)
Although the function of the mastoid cavity has long been debated, it is thought that the mastoid cavity maintains the middle ear air pressure and aids in effective sound conductivity.2,10) Maintaining of the mastoid cavity air space and preserving the middle ear mucosa may prevent development of negative middle ear pressure during transient ET dysfunction. Therefore, it is important to restore a mastoid cavity with good aeration to prevent negative pressure in the middle ear and to obtain better post-operative hearing results as well.
At the first stage of the operation, we removed the incus and the malleus to making the route for silastic sheet, which also could enhance exposure of the epitympanum and the sinus tympani and help complete disease eradication. In this study, there was no recurrence of cholesteatoma in all patients, which was clinically meaningful. However, in order to evaluate the efficacy of this technique more thoroughly, further follow up studies are warranted, because the recurrence rate increase with the follow-up time especially after more than 3 years.11)
To enhance mastoid cavity and middle ear aeration, some surgical procedures, such as anterior tympanotomy, posterior tympanotomy, and insertion of a silastic sheet in the middle ear and mastoid cavity, have been developed. Silastic sheet insertion between the mesotympanum and the epitymapnum or the antrum during the first stage of the operation could enhance mastoid cavity aeration.12,13) A silastic sheet was used to prevent adhesions between tympanic grafts and the raw bony surface of the middle ear and to allow normal mucosal regeneration to take place in the middle ear. Sheehy concluded that a thick silastic sheet (0.04 inches) insertion was preferred in extensive mucous membrane destruction and a staged operation.1) A thick silastic sheet is stiffer than a thin silastic sheet (0.005 inches) so that it will not be deformed by fibrous tissue, but is removed at the second stage of the operation. In the current study, a thinner (0.02 inches) silastic sheet was used and placed from the ET to the mastoid through the facial recess. After insertion of the silastic sheet in the first stage of the operation, middle ear aeration increased significantly (the average middle ear aeration was 0.60 before the first stage of the operation and 2.32 before the second stage of the operation), which was occurred in patients with COM, cholesteatoma, and adhesive otitis media. Complications of the silastic sheet insertion are tympanic membrane perforation by deformity or displacement and a foreign body reaction, but there were no complications, except one case which was shown to be tuberculous otitis media and healed by antituberculosis medication.
The ET function is known to have an influence on aeration of the middle ear after surgery. However, ET function did not influence the post-operative aeration grade in this study.
To achieve successful ossiculoplasty, the second stage of the operation was performed more than 6 months after the first stage of the operation. In the current study, hearing results after ossiculoplasty with Polycel
® achieved an ABG ≤ 30 dB in 84.8% of the patients and an ABG ≤20 dB in 67.3% of the patients. This results was the same as House's staged operation hearing results.14) 

Conclusion

A long silastic sheet insertion from the mastoid to the middle ear is statistically effective for amelioration of tympanic cavity and mastoid aeration after the first stage of the operation. A long silastic sheet is useful for operations involving chronic middle ear disease with poor mastoid aeration. We are currently pursuing a long-term study in a larger series of patients to further examine the efficacy of this technique.


REFERENCES
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  8. Sanna M, Zini C, Gamoletti R, Delogu P, Scandellari R, Russo A, et al. Prevention of recurrent cholesteatoma in closed tympanoplasty. Ann Otol Rhinol Laryngol 1987;96:273-5.

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  10. Tumarkin A. On the nature and vicissitudes of the accessory air spaces of the middle ear. J Laryngol Otol 1957;71:211-48.

  11. Mishiro Y, Sakagami M, Kitahara T, Kondoh K, Okumura S. The investigation of the recurrence rate of cholesteatoma using KaplanMeier survival analysis. Otol Neurotol 2008;29:803-6.

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  13. Kazama K, Takahashi H, Kaieda S, Iwanaga T, Yamamoto-Fukuda T, Yoshida H, et al. Effect of a large-sized silicone sheet upon recovery of mastoid aeration after mastoidectomy. Otolaryngol Head Neck Surg 2008;138:738-42.

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